Chapter I. PHYSICAL FEATURES

• Study of India’s stratigraphical geology requires understanding its principal physical features.
• Familiarity with geography, relief, mountain systems, plateaus, plains, drainage systems, glaciers, and volcanoes is essential.
• Physical or geographical maps are indispensable for this study.
• India is composed of three distinct geological and physical units:

1. 1. Peninsula (Deccan), including Ceylon, with a unique geological history since the Cambrian period.
   2. Himalayan mountainous region, bordering western, northern, and eastern India, extending into Afghanistan, Baluchistan, and Burma.
   3. Indo-Gangetic Plain, stretching from the Indus Valley in Sind to the Brahmaputra Valley in Assam, separating the Peninsula and the Himalayas.

• • Peninsula India has horizontally reposed rock-beds with minimal folding, primarily fractured in blocks due to tension or compression.
• Extra-Peninsula (Himalayan region) exhibits extensive folding, faults, and thrust-planes, indicative of significant compression and upheaval.
• Physiography differs markedly: Peninsula has “relict” mountains and shallow river valleys nearing base-level erosion.
• Extra-Peninsula features true tectonic mountains, rapid rivers with deep gorges, and ongoing erosion.
• Peninsula represents a Horst type crust, stable with vertical movements, while extra-Peninsula shows lateral thrusts and surface folding.
• Indo-Gangetic Plains consist of recent alluvial deposits from the Himalayan rivers, covering deeper geological records.
• Rajputana in western India shares characteristics of both Peninsula and extra-Peninsula, debatable in classification.
• Aridity in Rajputana has led to desert topography, isolated from moisture-bearing monsoons.
• Evidence suggests the Indus basin was once connected to the Peninsula before desertification, with ancient river-beds indicating past fertile conditions.

• Himalayan mountain ranges originated from external earth-movements, influenced by the Peninsula’s old crystalline rocks.
• Formation primarily due to powerful lateral thrusts from the north, pressing fold after fold against the Peninsula.
• Curved shape of Himalayas due to resistance from Peninsula’s “foreland,” aided by Aravalli mountains and Assam ranges.
• Main structural feature: parallel reversed faults or thrust-planes, notably the Main Boundary Fault.
• Geography: Himalayas not a single chain but several parallel or converging ranges with vast valleys and plateaus.
• Width between 100 and 250 miles, Central axial range (Great Himalaya range) spans 1500 miles.
• Northern slopes dense with forest vegetation, southern slopes steep and barren except in valleys.
• Pamir Massif links Himalayas to other Central Asian ranges (Hindu Kush, Karakoram, etc.), known as “roof of the world.”
• Eastern Himalayas rise abruptly from Bengal plains, peaks like Kanchenjunga and Everest visible from the plains.
• Western Himalayas rise gradually via mid-Himalayan ranges, peaks more than a hundred miles distant from plains’ view.
• Meteorological influence: moderates temperature and humidity in Northern India, crucial for precipitation from monsoons.
• Glaciers feed rivers that sustain fertile plains, shielding India from arid conditions spreading from Tibet and Central Asia.
• Geographic limits: generally from Indus bend in Kashmir to Brahmaputra bend in upper Assam, with debated extensions.
• Syntaxial Bends: structural interest in abrupt changes in Himalayan trend lines, influenced by geological formations and bends.
• Western syntaxis shows significant geological formations bending south and southwest from Nanga Parbat to Hazara.
• Eastern syntaxis beyond Assam indicates bends from easterly to southerly trends, affecting Arakan Yomas towards Fort Hertz.
• Geological formations and bends suggest complex tectonic history shaping Himalayan range configurations.
• Geographical division by Burrard: Punjab Himalayas (Indus to Sutlej, 350 miles), Kumaon Himalayas (Sutlej to Kali, 200 miles), Nepal Himalayas (Kali to Tista, 500 miles), Assam Himalayas (Tista to Brahmaputra, 450 miles).
• Classification into three longitudinal zones: Great Himalaya (highest peaks, e.g., Everest, K2), Lesser Himalayas (lower elevation, closely related to Great Himalaya), Outer Himalayas (Siwalik ranges, low foot-hills).
• Geological structure: Northern Zone (Tibetan, marine sedimentary rocks from Palaeozoic to Eocene), Central Zone (Himalayan, crystalline and metamorphic rocks), Outer Zone (Sub-Himalayan, Tertiary sedimentary river-deposits).
• Reference to Burrard and Hayden’s comprehensive works on Himalayan geography and geology.
• Extra-Peninsula ranges: West (Salt-Range, Suleiman range, Bugti range, Kirthar range), East (Assam ranges, Manipur ranges, Arakan Yoma, Tenasserim range).
• Mostly simple mountain-structure, Tertiary rock composition, except Salt-Range and Assam ranges.
• Peninsula ranges: Aravalli mountains (true tectonic chain), Vindhyas, Satpuras, Western Ghats (Sahyadris), Eastern Ghats.
• Aravallis: old Palaeozoic and Mesozoic geography, deeply eroded remnants.
• Vindhyas and Kaimur range: horizontally bedded sedimentary rocks, ancient age, similar to Torridon sandstone.
• Satpuras: “seven folds,” basalts, granitoid and metamorphic core, possible tectonic origin like Aravallis.
• Western Ghats: steep-sided cliffs facing Arabian Sea, terraced, flat-topped hills, mean elevation around 3000 feet.
• Nilgiris and Anaimalai hills: rounded, undulating outline, sub-tropical forest vegetation, composed of ancient crystalline rocks.
• Eastern Ghats: discontinuous, facing Bay of Bengal, varied geological formations, no unified structure, remnants of ancient mountain-chains.
• Other Peninsula ranges: Rajmahal hills (trap-built), Nallamalai hills (gneissose granite), Shevaroys and Pachamalai (gneissic plateau).

• Snow-line altitude variation: Eastern Himalayas around 14,000 feet, western side up to 19,000 feet; Tibetan side about 3,000 feet higher, due to dry conditions and monsoon wind moisture absence.
• Ladakh snow-line at 18,000 feet; Hindu Kush average at 17,000 feet.
• Lesser Himalayas below 15,000 feet do not support present glaciers; evidence of past glaciation in Pir Panjal range.
• Great Himalaya feeds numerous glaciers, some among world’s largest outside Polar regions; extensive scientific study ongoing.
• Glacier sizes vary widely: majority 2-3 miles, largest like Milam, Gangotri, and Zemu up to 24 miles.
• Karakoram glaciers largest in Indian region: Hispar, Batura (36-38 miles), Biafo, Baltoro (37 miles), Siachen, Remo (45 miles), Fedchenko (Pamir, similar dimensions).
• Ice thickness: Baltoro 400 feet at end, deeper towards middle; Zemu 650 feet; Fedchenko nearly 1800 feet.
• Karakoram glaciers relics of last Ice Age; diminishing due to insufficient snowfall.
• Glacier types: valley glaciers predominant; hanging glaciers not uncommon.
• Glacier behavior: longitudinal glaciers larger, less sensitive to seasonal changes; transverse glaciers shorter, fluctuating, lower descent (7,000-8,000 feet in Kashmir).
• Terminal moraines at various altitudes: Kanchenjunga 13,000 feet, Kumaon and Lahoul 12,000 feet, Kashmir as low as 7,000 feet.
• Factors influencing glacier limits: latitude decrease from Karakoram (36°) to Kanchenjunga (28°), rain instead of snow in eastern Himalayas.
• Peculiarities: extensive superficial moraine cover, shepherds camp on moraines; englacial and sub-glacial moraine presence, glacier motion 3-5 inches at sides, 8 inches to 1 foot in middle.
• Glacier dynamics: retreat observed with terminal moraine evidence; occasional advances noted.
• Mason’s study: glacier velocity varies, no regular periodic variation related to weather cycles.
• Summer melting leads to englacial and sub-glacial drainage, forming ice-caves.
• Past glaciation records: present glaciers remnants of older, more extensive ice system; moraine debris, U-shaped valleys, cirques, and ancient moraines visible in middle Himalayas, suggesting Pleistocene Glacial Age presence in India.

• Rivers and tributary-systems main drainage channels and erosion agents, transporting land waste to sea.
• Peninsular and extra-Peninsular India drainage systems differ significantly due to varied topography.
• Peninsular rivers ancient, nearing base-level stage, broad, shallow valleys due to vertical erosion cessation.
• Lateral erosion significant; rivers deposit silt in basins, alluvial banks, estuarine flats.
• Peninsula rivers mature or adult stage, uniform erosion curve from source to mouth.
• Eastern trend notable: Western Ghats watershed, rivers flow towards Bay of Bengal despite proximity to Arabian Sea.
• Hypotheses: Peninsula’s easterly drainage anomaly due to ancient landmass submerged under Arabian Sea, or fault-plane utilization by Narbada and Tapti rivers.
• Narbada and Tapti exceptional: flow west, utilize fault-planes parallel to Vindhyas due to northern Peninsula tilt during Himalayan uplift.
• Alluvial margin: scanty on western coast except Gujarat; wide on east coast with extensive deltaic deposits at Mahanadi, Godavari, Kistna, Cauvery mouths.
• Coast peculiarities: absence of deltas at Narbada and Tapti mouths due to strong monsoon gales and tidal currents.
• Ceylon contrast: radial drainage from central highlands, rivers flow outward in all directions.
• Himalayan drainage system post late Tertiary mountain-building, differs significantly from Peninsula.
• Rivers in extra-Peninsula both erode and deposit agents, forming North India plains from mountain silt.
• Not consequent drainage: rivers older than current terrain, maintained own channels during mountain formation.
• Himalayan drainage antecedent: rivers predate mountains, erosion and uplift occurred simultaneously.
• Transverse gorges deep, cutting through highest peaks, characteristic of Himalayan geography.
• Himalayan watersheds far north of peak line, drain both southern and northern Tibetan slopes.
• Examples: Indus valley, deep defile between 20,000 ft precipices, river bed much lower at Hyderabad.
• Other gorges: Sutlej, Gandak, Kosi, Alaknanda, deep defiles 6000-12,000 ft depth, narrow width.
• Transverse gorges origin debated: initially thought fissures widened by water, or lakes formed by Himalayan uplift.
• River capture evident: main rivers capturing tributaries, e.g., Bhagirathi, Arun, Tista, Sind river.
• Hanging valleys in Sikkim and Kashmir: side valleys higher than main stream, formed by rapid head-erosion and river capture.
• Glacial influence protects hanging valleys from river erosion, maintaining level differences.

• Lakes play very little part in the drainage system of India.
• Even in the Himalayas, lakes of notable size are very few.
• Principal lakes of extra-Peninsula include those of Tibet, Kumaon, and Kashmir.
• Manasarovar and Rakas Tal are the reputed sources of the Indus, Sutlej, and Ganges.
• Manasarovar covers 200 sq. miles, and Rakas Tal covers 140 sq. miles.
• Gunchu Tso, a saline lake, is 15 miles long and has no outlet.
• Other lakes include Yamdok Cho, Chamtodong, Nainital, Bhim Tal, and lakes in Kashmir like Pangkong, Tsomoriri, Salt Lake, Wular, and Dal.
• The origin of Tibetan lakes is debated: damming by alluvial fans, elevation of river-bed, or glacial erosion.
• Kumaon lakes’ origins are uncertain, possibly due to earth movements or landslips.
• Kashmir’s small freshwater lakes are inundated hollows in the Jhelum’s alluvium.
• Manchar lake of Sind, a shallow depression, forms part of the Indus drainage system.
• Tibetan lakes show increasing salinity and diminishing volume since late geological times.
• Salinity is due to lack of drainage outlets and high solar evaporation.
• Desiccation of Tibetan lakes observed by old high-level terraces and beaches.
• Desiccation attributed to glacier disappearance and Himalayan uplift.
• Peninsula lakes of note include Rajputana’s salt-lakes and Lonar’s crater-lake.
• Sambhar salt-lake is the largest in Rajputana, covering 90 sq. miles during the monsoon.
• Sambhar lake’s salinity is due to wind-borne salt from sea spray and the Rann of Cutch.
• 130,000 tons of saline matter is annually carried by winds to Rajputana.
• Lonar lake is a deep crater-like hollow in the basalt-plateau of the Deccan.
• Lonar lake’s water contains sodium carbonate and sodium chloride.
• Lonar lake’s hollow is thought to be due to a volcanic explosion or subsidence into a cavern.

• The coasts of India are comparatively regular and uniform, with few creeks, inlets, or promontories of any magnitude.
• The Malabar coast has several lakes, lagoons, or back-waters, such as the Kayals of Travancore.
• These back-waters are shallow lagoons or inlets of the sea lying parallel to the coast-line.
• They provide important facilities for inland water-communication on the Malabar coast.
• Monsoon floods bring silts that support large forests and plantations along their shores.
• Remarkable mangrove-swamps line the coasts, especially along tidal estuaries, deltaic fronts, or salt-marshes.
• The sea-board is surrounded by a narrow submarine ledge or platform known as the “plain of marine denudation” where the sea is very shallow, with soundings less than 100 fathoms.
• This shelf is broader on the Malabar and Arakan coasts than on the Coromandel coast.
• The sea-bed gradually deepens from these plains to a mean depth of 2000 fathoms in the Bay of Bengal and 3000 fathoms in the Arabian Sea.
• The seas originated from earth-movements in the Cretaceous or early Tertiary times, forming bays or arms of the Indian Ocean that overspread areas of Gondwanaland.
• The coastline in front of the Indus and Ganges deltas is changeable due to the struggle between delta growth and wave erosion.
• Extensive mangrove-swamps are a feature of these coasts.
• The coast of Sind forms part of the plain of marine denudation, with shallow seas.
• The escarpment of the Western Ghats parallel with the Malabar Coast is believed to be formed by scarp-faulting.
• The Mekran coast of Baluchistan is largely shaped by an E.-W. fault.
• The south-east coast of Arabia and the Somaliland coast are determined by scarp-faults.
• The north border of the Arabian Sea is surrounded by steep fractures of Pliocene or later age.
• The Murray Expedition of 1933-34 revealed intermittent submerged ridges, 10,000 feet high, 60 miles from the Mekran coast.
• Two parallel ridges separated by a deep rift valley extend from Karachi to the Gulf of Oman.
• These ridges are in tectonic continuation with the Kirthar range of Sind.
• Colonel Sewell noted similarities between the Arabian Sea floor and the Rift Valleys of East Africa.
• Geodetic data suggest the Laccadive archipelago is a continuation of the Aravalli mountains’ axes.
• The islands in the seas are continental, except for the coral islands, Maldives, and Laccadives, which are atolls or barrier-reefs.
• Barren Island and Narcondam are volcanic islands east of the Andamans.
• The low level and smooth contours of the tract below the Mahanadi suggest it was a submarine plain that emerged recently.
• Behind this coastal belt are the gneissic highlands of the Eastern Ghats.
• The old shore-line lies between the coastal belt and the Eastern Ghats.
• The Arakan coast of the Bay of Bengal features drowned valleys and deep inlets due to recent depression.
• The islands of this coast and the Malay archipelago are unsubmerged portions of a once continuous land stretch from Akyab to Australia.

• No active volcanoes exist in the Indian region.
• Barren Island in the Bay of Bengal is a dormant volcano with a truncated cone and caldera.
• Barren Island’s summit crater is about 1000 feet above sea level, with its base thousands of feet underwater.
• Last eruption of Barren Island was in the early 19th century, now in a solfataric phase.
• Narcondam is another volcano in the region, composed of andesitic lavas, and is extinct.
• Popa is a large extinct volcano in Burma, composed of trachytes, ashes, and volcanic breccia.
• Koh-i-Sultan in western Baluchistan is another large extinct volcano.
• Unverified records exist of living and dormant volcanoes in Central Tibet and the Kuen-Lun range.
• Lonar crateriform lake is connected with volcanic action.
• Mud-volcanoes occur in the Irrawaddy valley, Arakan coast of Burma, and Mekran coast of Baluchistan.
• Mud-volcanoes discharge hydrocarbon gases, muddy saline water, and traces of petroleum.
• Conical mounds of mud-volcanoes are common on the Ramri and Cheduba islands of the Arakan coast.
• Mud-volcano cones in Minbu, Burma, reach about forty feet; in Baluchistan, some are nearly 300 feet high.
• Most mud-volcanoes have a gentle flow of muddy water but can have violent outbursts.
• Mud-volcano gas has the same origin as petroleum, with many near oilfields or petroleum seepages.
• Mud-volcanoes often occur near the crests of anticlinal folds or fault lines.
• In Burma’s Yenangyaung oilfield, dried mud veins represent channels of long-gone mud-volcanoes.
• Mud in mud-volcanoes comes from disintegration of Tertiary age shales associated with gas-bearing strata.
• Mud-volcanoes form prominent features in dry climates with easily disintegrated shale and small water flow.
• Some mud-volcanoes result in dirty water pools without permanent cones, as seen in Assam.
• Mud-volcanoes are common near petroleum in Russia and the Dutch East Indies.

• Few earthquakes have visited the Peninsula since historic times; however, the extra-Peninsula has experienced many.
• Most Indian earthquakes originate from the great plains of India or their peripheral tracts.
• Notable historical earthquakes: Delhi (1720), Calcutta (1737), Eastern Bengal and Arakan coast (1762), Cutch (1819), Kashmir (1885), Bengal (1885), Assam (1897), Kangra (1905), North Bihar (1934), West Baluchistan (1935).
• These areas are zones of weakness and strain due to recent crumpling of rock-beds in the Himalayas.
• The region is a belt of underload, with rocks about 18% lighter than normal, falling within the global east-west earthquake belt.
• The Assam Earthquake (1897) was one of the world’s most disastrous earthquakes, with a disturbed area of 1,600,000 sq. miles.
• Shillong and 150,000 sq. miles around it were devastated in less than a minute.
• Communications were destroyed, plains were riddled with rents and flooded, and hill-sides scarred by landslips.
• The seismic motion was a complicated undulatory movement with significant vertical and horizontal components.
• Wide earth-fissures opened in the plains, emitting water and sand, disrupting drainage and causing flooding.
• Hundreds of aftershocks followed the main shock, originating from shifting foci over a large epicentral tract.
• Structural changes included fault-scarps, fractures, local level changes, and new lakes along the Chidrang river.
• R. D. Oldham suggested multiple foci over a tract 200 miles long and 50 miles wide with numerous branch-faults.
• The velocity of earth-waves was about 2 miles per second, with the main shock originating at a depth of 5 miles or less.
• The Kangra Earthquake (1905) was felt over northern India, with exceptional violence and destructiveness along two linear tracts.
• The epifocal tracts were Kangra-Kulu and Mussoorie-Dehra Dun, with ellipsoidal isoseists.
• The quake velocity was about 1.92 miles per second, with a deep-seated origin at depths of 21 to 40 miles.
• Aftershocks were numerous and persisted for years, with geological effects including minor level changes and landslips.
• The cause was a tectonic quake due to slipping or strain change along faults parallel to the Main Boundary Fault of the Himalayas.
• The North Bihar Earthquake (1934) caused extensive destruction and affected an area of 1,900,000 sq. miles.
• Main epicentra were Motihari-Madhubani, Kathmandu, and Monghyr.
• The quake caused extensive fissures, sand-vents, flooding, and significant loss of life, with estimates exceeding 12,000.
• The West Baluchistan (Quetta) Earthquake (1935) caused severe local destruction, especially in Quetta, killing 20,000 people.
• The epicentral tract was about 68 miles long and 16 miles broad, with damage intensity decreasing rapidly from the epicentre.
• Rock-falls and ground fissuring occurred, but no marked upheavals; the earthquake was tectonic in nature.
• The region’s seismic instability is due to the strain on rock-folds from the festooned tectonic axes around a pivot near Quetta.
• Few hypogene disturbances have interfered with the stability of the Peninsula as a continental land-mass for an immense length of geological time.
• Minor movements of secular upheaval and depression have occurred along the coasts in past and recent times.
• The most important movement is the slight but appreciable elevation of the Peninsula, exposing marine denudation plains as a shelf or platform around its coasts.
• Raised beaches are found at altitudes of 100 to 150 feet at many places around the coasts of India.
• A common type of raised beach is the littoral concrete, composed of gravel, sand with shells, and coral fragments.
• Marine shells are found at several places inland at heights far above the level of the tides.
• The steep face of the Sahyadri mountains suggests they are sea-cliffs formed by recent elevation and subsequent sea-action.
• Marine and estuarine deposits of post-Tertiary age are found towards the southern extremity of the Peninsula.
• There are proofs of minor, local alterations of level, both elevation and depression, in sub-recent and prehistoric times.
• Lignite and peat beds in the Ganges delta and peat deposits near Pondicherry are proofs of slow movements of depression.
• Submerged forests discovered on the eastern coast of Bombay and similar forests on the Tinnevelli coast indicate depression.
• The thick bed of lignite at Pondicherry and layers of vegetable debris in the Ganges delta indicate slow depression.
• The sea deepens suddenly to a great hollow about twenty miles from the Mekran coast, suggesting submergence of a cliff.
• The 1819 subsidence of the western border of the Rann of Cutch, creating the Allah Bund, is a notable event of land elevation and depression.
• The 2000 square mile area was suddenly depressed to 12-15 feet, converting it into an inland sea, with Sindree fort submerged.
• An area of 600 square miles was simultaneously elevated, forming the “Allah Bund.”
• The Madhupur jungle near Dacca is believed to have been upheaved by 100 feet recently, causing the Brahmaputra river’s deflection.
• The Rann of Cutch was a gulf of the sea within historic times, gradually silted up and converted into a low-lying tract.
• The branching inlets of the sea in the Andaman and Nicobar islands indicate submergence within late geological times.
• Good examples of drowned valleys occur on the Arakan coast, with estuaries and inlets indicating recent submergence.
• In some creeks of Kathiawar near Forbander, oyster-shells were found above the present height of tides.
• Barnacles and serpulae were found at levels not now reached by the highest tides in Kathiawar.
• Oyster-banks in Sind and oyster-shells in Calcutta indicate a slight local rise of the eastern coast.
• Some geologists believe the Himalayas are still experiencing changes in level and have not yet reached their maximum elevation.
• Many rivers show recent rejuvenation due to the uplift of their watershed.
• Frequent and violent earthquakes in the Himalayas and adjacent tracts indicate ongoing tension and instability in the strata.

• India is favourably circumstanced for the study of geodesy due to its triangular shape and stretch of 1700 miles over one meridian.
• The deformation of the geoid in India shows abnormal variations in the direction of gravity, particularly in Northern India and Ferghana.
• In India, it was discovered that a deficiency of matter underlies the Himalayas, while dense matter runs south of the Indo-Gangetic plains.
• Sea-ward deflections of the pendulum prevail around the coasts of Deccan rather than towards the Ghats.
• The theory of mountain compensation was formulated in India in 1854 by Rev. J. H. Pratt, leading to the doctrine of isostasy.
• Isostasy implies a hydrostatic balance between different segments of the earth’s crust and an adjustment between surface relief and density.
• Continents, plateaus, and mountains are composed of relatively light material, causing them to float, while ocean basins are composed of dense material, causing them to depress.
• Extra loads on the surface, like ice-sheets, cause sinking, while prolonged denudation causes rising until equilibrium is established.
• The depth of isostatic compensation in the USA is about 76 miles (113.7 km), but in India, it varies due to geological differences.
• Plumb-line and pendulum observations show discrepancies in deflections due to the Himalayas, indicating partial compensation.
• The outer and middle Himalayas are under-compensated, while the central ranges are over-compensated.
• In the Indo-Gangetic plains, deflections are towards the south, suggesting a chain of dense rock beneath the plains.
• Gravity measurements confirm the main postulates of isostasy but show large anomalies in India not explained by surface features.
• Gravimetric surveys in North India show belts of excess and defects of density not represented by surface features.
• An alternative hypothesis of sub-crustal warping has been proposed to account for these anomalies.
• India as a whole is an area of defective density, with gravity in deficit by a stratum of rock 600 feet thick over an area of two million square miles.

• Monsoonic alternations are a unique feature in India’s meteorology, dividing the year into a wet half (May to October) and a dry half (November to April).
• The wet half is characterized by moist, vapour-laden winds from the south-west, while the dry half features retreating dry winds from the north-east.
• These monsoonic alternations significantly influence the character and rate of subaerial denudation in India.
• Laterite, a peculiar form of regolith, covers the entire Peninsula from the Ganges valley to Cape Comorin and results from the subaerial alteration of surface rocks under monsoonic weather.
• Other weathering products include the red soil of Madras, black soil (regur) in South India, and Reh efflorescences and nitre formation in North India.
• The general atmospheric weathering or denudation in India is characteristic of the tropical or sub-tropical zone.
• India has diverse climates, ranging from torrid heat in Punjab and Baluchistan to Arctic cold in the higher Himalayas.
• Rock disintegration predominates in dry areas, while rock decomposition occurs in humid, monsoon-swept areas.
• Desert regions like Rajputana, Sind, and Baluchistan experience mechanical disintegration due to drought, insolation, and wind action.
• The transporting power of winds in these regions is enormous, carrying vast quantities of fine detritus and contributing to the loess deposits in N.W. India.
• The geological action of winds in Rajputana is significant, illustrating the evolution of desert topography and aeolian action since Pleistocene times.
• Indian rivers accomplish significant erosion during the wet half of the year, transporting enormous loads of silt to the sea.
• The Ganges conveys over 356,000,000 tons of sand and clay annually, while the Indus and Brahmaputra also carry substantial amounts of silt.
• Rivers also transport chemically dissolved matter, including salts, from the land to the sea.
• The salinity of river waters varies, with the Mahanadi river having 86 parts of salts per million parts of water.
• Indian rivers experience extraordinary floods, especially in the spring and monsoon seasons, due to the absence of lakes that could restrain river-floods.
• Historical floods, such as those of the Indus in 1841 and 1858, caused massive destruction due to sudden torrents.
• Floods are often caused by landslides blocking rivers, creating temporary lakes that burst and cause severe flooding.
• Examples include the Alaknanda river in 1893, the Sutlej in 1819, and the Shyok river in 1924, 1927, and 1930.
• The increased volume and velocity of water during floods enhance the erosive and transporting power of rivers, moving large boulders and causing significant damage to banks and riverbeds.
• Many changes in the chief drainage lines of North India since late Tertiary times have resulted in a complete reversal of river flow directions.
• The Siwalik deposits along the foot of the Himalayas from Assam to Sind are attributed to a great north-west-flowing river named the “Siwalik River” or “Indobrahm.”
• This old river succeeded the narrow strip of the Himalayan sea, with deposits of Murree and Siwalik formed between the Middle Miocene and end of Pliocene.
• Post-Siwalik earth-movements dismembered this river system into the present Indus, its five Punjab tributaries, and rivers of the Ganges system.
• Elevation of Potwar plateau converted the north-west section of the main river into a separate basin with the Sutlej as its tributary.
• The main river’s upper portion reversed flow, seeking an outlet into the Bay of Bengal along the sub-montane plains.
• River-capture by head-erosion and differential earth-movement contributed to this drainage reversal.
• The severed upper part of the Siwalik River became the modern Ganges, capturing the transversely running Jumna.
• Transverse Himalayan rivers continued discharging into the new river regardless of its destination.
• During sub-Recent times, some interchange occurred between Indus’ easterly affluents and Jumna’s westerly tributaries.
• The Jumna historically discharged into the Indus system through the Saraswati river, its current course to Prayag being recent.
• The Punjab’s Jhelum, Chenab, Ravi, Beas, and Sutlej originated after the Siwalik system uplift and Indus-Ganges severance.
• Potwar plateau uplift rejuvenated southern Punjab’s rivulets, which captured parts of the Siwalik River, forming the five Punjab rivers.
• The Soan river occupies the western portion of the deserted main river channel, mismatched with its basin size.
• The Himalayas, undergoing active subaerial erosion due to recent folding and fracture, erode rapidly compared to older geological features.
• The plains of India and the Ganges delta measure the Himalayas’ erosion since the Pliocene period.
• Landslips, soil-creep, and block break-offs are common in the Himalayas, with intense denudation in the Eastern Himalayan forests.

• Correlating Indian rock systems with the European stratigraphical scale is difficult, especially without fossil evidence.
• Determining geological horizons in the Peninsula and the outer Himalayas often relies on lithological composition, structure, and degree of metamorphism.
• These tests are unsatisfactory but necessary for the pre-Cambrian formations of the Peninsula.
• Stratigraphy involves determining the natural order of superposition of strata for correlation.
• Complications arise from folding, faulting, and lateral variations of sedimentary strata.
• William Smith’s discovery that strata are characterized by specific fossils laid the foundation of historical geology.
• Criteria for correlating formations include: order of superposition, fossil organisms, lithological characters, stratigraphical continuity, unconformities, degree of metamorphism, and tectonic disturbance.
• Establishing absolute contemporaneity between distant rock-systems is not feasible due to differing rates of biological evolution and species distribution.
• Rock-records in India should be arranged chronologically and classified using local breaks or organic remains.
• Outcrops should be correlated among themselves and with the standard stratigraphy scale based on fossils or lithological grounds.
• The Carboniferous system of Europe is characterized by specific fossils; similar fossils in India indicate a correlation, though the strata may have local names.
• Geological synchronism is less significant than pointing to the same epoch in life’s history.
• The order of life-forms’ appearance is broadly uniform globally, providing some unity between rock-groups.
• Prof. Huxley introduced “Homotaxis” to denote “Similarity of arrangement” in the geological series.
• Jurassic fauna and flora in Europe are homotaxial with deposits in India, regardless of their actual age relative to Triassic or Cretaceous deposits elsewhere.
• Geological formations in different districts of India can be composed of various types of deposits, known as different facies, e.g. calcareous, argillaceous, arenaceous facies.
• There can also be different facies of fauna, named after the dominant element, e.g. coralline facies, littoral facies.
• Rocks of the same system or age in India may have different facies due to diverse physical conditions at sedimentation centers.
• Example: The Gondwana system in the Peninsula is fresh-water and subaerially deposited with ferns, conifers, fishes, and reptiles.
• The same age rocks in the Himalayas are marine limestones and calcareous shales with deep-sea organisms, grouped into Upper Carboniferous, Permian, Triassic, and Jurassic systems.
• The Salt-Range often shows coastal facies with clays, sandstones, and littoral organisms alternating with limestones.
• Homotaxial deposits may differ in fossil content due to differing marine, littoral, and pelagic organisms and physical barriers to species migration.
• Fossils in deposits are influenced by three variables: geological period, zoological/botanical provinces, and physical conditions (depth, salinity, muddiness, temperature, sea-bottom character).
• Radioactive minerals (uranium, thorium) can help determine the age of pre-Cambrian systems in India through lead-ratio and helium-ratio analysis.
• Chief geological provinces of India include:
• The Salt-Range: well-explored with most geological systems displayed; important for stratigraphy and paleontology.
• The Himalayas: Tibetan zone with a complete geological record from Cambrian to Eocene; notable areas are North-West Himalayas (Hazara, Kashmir, Pir Panjal) and Central Himalayas (Simla hills, Spiti, Kumaon, Garhwal).
• Sind: highly fossiliferous marine Cretaceous and Tertiary record; Sind-Baluchistan frontier has a well-developed Tertiary sequence.
• Rajputana: full sedimentary record, three pre-Palaeozoic systems, isolated marine Mesozoic and early Tertiary strata.
• Burma and Baluchistan: large sections of the stratified marine geological record, aiding in filling gaps in the Indian sequence.
• Coastal System of India: marine sediments along the eastern and Mekran coasts, records of successive marine transgressions.
• Peninsular India: imperfect geological record, mainly fluviatile, terrestrial, volcanic accumulations, with a significant Cretaceous record and partly Eocene Deccan Traps.
• Students should familiarize themselves with representatives of geological systems in these provinces correlated to European sequences.
• Geological systems should be studied in the context of processes and actions that formed them, using modern dynamics for interpretation.
• Fossil shells and rock particles tell the history of earth’s natural operations, evolution, geography, and climate of their time.
• Stratigraphical geology should include principles of dynamical and tectonic geology, structural geology, crust-deformations, vulcanicity, life-form variations, migrations, and extinctions.

• Oldest rocks on earth’s crust found at bottom of stratified deposits globally exhibit similar characteristics: azoic, crystalline, contorted, faulted, intruded by plutonic masses, with foliated structure.
• Archaean rocks also known as “Fundamental Complex” or “Basement Complex”.
• Origins of Archaean rocks unclear, theories include: consolidation of gaseous/molten planet crust, early sediments under different atmospheric/oceanic conditions, metamorphism of plutonic masses, consolidation of original heterogeneous magma.
• Distribution in India: predominant in Peninsula, central and southern regions, also in north-east (Orissa, Central Provinces, Chota Nagpur), north (Bundelkhand), and north-west (Baroda to Aravallis and Rajputana).
• In extra-Peninsula, prominent along entire Himalayan length, forming highest ranges, central to mountain system from Kashmir to Burma.
• Uncertainty in identifying true Archaean zones in Himalayas due to metamorphosed late Mesozoic or Tertiary intrusives.
• Similar broad crystalline zone in Burma, including Martaban system and Mogok gneiss.
• Petrology: predominant rock is gneiss, varying in mineral composition from granite to gabbro, characterized by foliated or banded structure.
• Gneiss structure attributed to alternating bands of constituent minerals or layers of varying mineral composition.
• Gneiss shows variability in composition, structure: intrusive granite appearance, varying levels of foliation or schistosity, texture from coarse holocrystalline to fine-grained felsite.
• Constituent minerals of Archaean gneiss: orthoclase, oligoclase or microcline, quartz, muscovite, biotite, hornblende; accessory minerals include tourmaline, apatite, magnetite, zircon, chlorite, epidote, kaolin.
• Orthoclase predominant, gives pink or white color; plagioclase subordinate; quartz variable; hornblende and biotite common ferro-magnesian minerals.
• Gneiss composition variable: granite-gneiss, syenite-gneiss, diorite-gneiss, gabbro-gneiss.
• Gneisses transition to schists with disappearance of feldspars.
• Schists in Archaean system: mica-, hornblende-, talc-, chlorite-, epidote-, sillimanite-, graphite-schists; mica-schists most common, often garnetiferous.
• Less common Archaean rocks in India: granulites, crystalline limestones (marbles), dolomites, graphite, iron ores.
• Extensive basic trap-dykes of dioritic or doleritic composition traverse gneisses and schists.
• Indian Archaean complex not uniform: includes ortho-gneisses (deformed plutonic equivalents), para-gneisses (metamorphosed sediments), possibly original crust.
• Factors in Indian Archaean: ancient basement complex, intruded plutonic rocks (Charnockites, Bundelkhand gneisses), highly metamorphosed para-gneisses and schists, likely Dharwar age.
• Petrological types associated with Archaean gneisses and schists discovered in Indian Geological Survey:
• Granite.
• Augite-granite (Laurvikite).
• Nepheline-syenite.
• Elaeolite-syenites and their pegmatites.
• Corundum-syenite.
• Charnockite.
• Augite-norite.
• Norite.
• Hyperite.
• Olivine-norite.
• Pyroxenite.
• Anorthosite.
• Granulite.
• Garnetiferous-leptynite.
• Pyroxene-diorite.
• Scapolite-diorite.
• Khondalite (Quartz + sillimanite + garnet + graphite).
• Gondite (Quartz + manganese-garnet + rhodonite).
• Rhodonite rock.
• Gondite of North Arcot, Madras, Rajputana, etc.
• Sivamalai series of Holland.
• Charnockite series of Madras and Bengal.
• Khondalite of Orissa, Central Provinces, etc.
• Gondite named by Dr. L. Fermor.
• Iron-ore and jasper or quartz schist.
• Anthophyllite, sillimanite, garnet gneisses.
• Kodurite (Orthoclase + manganese-garnet + apatite).
• Kodurite from Kodur in Vizagapatam district.
• Aluminous sediment with high magnesia content.
• Calc-gneiss, calciphyres and crystalline limestones.
• Quartz-haematite schist (Jaspilite).
• Quartz-magnetite schist.
• Cordierite-gneiss.
• Kyanite, chiastolite schist.
• “Streaky gneisses.”
• Felspathic gneiss.
• Pegmatites.
• Ultra-basic rocks.
• Chromite-bearing amphibolites.
• Quartzite.
• Phyllites.
• Groups of gneissic Archaean rocks in India:
• Bengalgneiss:
  • Highly foliated, heterogeneous, schistose gneisses and schists.
  • Found in Bengal, Bihar, Orissa, Carnatic, and large parts of the Peninsula.
  • Often dioritic with various associated schists.
  • Contains intercalated beds of limestones, dolomites, hornblende-rock, epidote-rock, corundum-rock, etc.
  • Abundance of accessory minerals like magnetite, ilmenite, schorl, garnet, calcite, lepidolite, beryl, apatite, epidote, corundum, micas, sphene.
  • Dome gneiss features dome-like hills from exfoliating rock.
  • Shows intrusive granite characteristics with local segregations and inclusions.
• Types of Bengal gneiss:
  • Sillimanite-gneiss and Sillimanite-schist of Orissa (Khondalites).
  • Includes schistose and garnetiferous gneiss in South India.
  • Examples in Bihar, Manbhum, Rewah, Carnatic, and Salem.
  • Carnatic gneiss includes micaceous, talcose, and hornblendic schists.
  • Considered one of the oldest members of the Archaean Complex.
• Bundelkhand gneiss:
  • Massive, granitoid gneisses primarily in Bundelkhand and parts of the Peninsula.
  • Resembles pink granite, minimal foliation.
  • Enormous area resembling intrusive granite.
  • Sparse association with hornblende-, talc-, and chlorite-schists.
  • Lacks interbedded marbles, dolomites, or quartzites.
  • Few accessory minerals in the mass or pegmatite-veins.
  • Traversed by coarse-grained diorite dykes and sills, extensive pegmatite-veins.
  • Characterized by long quartz-veins intersecting drainage-courses, forming small lakes.
  • Found in Peninsula under names like Balaghat gneiss, Hosur gneiss, Arcot gneiss, Cuddapah gneiss.
  • Used extensively as building stone historically.
• ite Series:
  • Plutonic granitoid rocks in South India.
  • Intrusions into older Archaean gneisses and schists of the Peninsula.
  • Found in Madras Presidency, including Nilgiris, Palnis, Shevaroys.
  • Medium to coarse-grained, dark-colored, basic holocrystalline granitoid gneisses.
  • Distinct mineralogical composition: rhombic pyroxene (hypersthene or enstatite), dark ferromagnesian compounds.
  • Common minerals: blue-colored quartz, plagioclases, augite, hornblende, biotite, garnets, zircon, iron-ores, graphite.
  • Varieties range from hypersthene-granite (Charnockite proper) to more basic pyroxenites.
  • Shows plutonic field characters: irregular or lenticular sills, uniform mineralogical composition.
  • Magmatic differentiation evidenced by basic secretions, acid excretions, and contemporaneous veins.
  • Contains apophyses and dykes protruding into surrounding older rocks.
  • Well-defined contact phenomena with invaded rocks like quartzites and limestone.
• Himalayan Archaean:
  • Forms bulk of high ranges in central Himalayas (Central zone).
  • Composed of crystalline or metamorphic rocks: granites, granulites, gneisses, schists.
  • Central gneiss known for intrusive origin into various geological formations.
  • Intrusions noted in Panjal Volcanic series (Permian), Jurassic, Cretaceous, and Eocene formations.
  • Dynamic metamorphism gives gneissic structure to granites.
  • Presence of highly metamorphosed ancient sediments (Purana sediments) complicates classification.
  • Majority likely intrusive granites marking special elevation zones during mountain uplift.

• During later Archaean era, Earth’s meteoric conditions changed gradually.
• Decreasing temperature condensed vapours, precipitating them on Earth’s surface.
• Condensed vapours collected in lithospheric hollows, forming first ocean.
• Further heat loss caused condensation in planet’s bulk, affecting outer crust.
• First-formed wrinkles and inequalities accentuated as oceans deepened.
• Land-masses, skeletons of first continents, rose above general surface.
• Geological agents of denudation began work on established seas and continents.
• Weathering of older Archaean gneisses and schists yielded earliest sediments.
• Deposited as Dharwar System in India, synonymous with metamorphosed Archaean sediments.
• Dharwar strata often rest over gneisses with great unconformity in some places.
• In others, interbedded with gneisses, sometimes older than gneisses.
• Dharwar strata generally unfossiliferous due to early age and metamorphism.
• Complex foldings of crust obliterated sedimentary traces, imparted crystalline, schistose structure.
• Extensively intruded by granitic bosses, veins, sheets, dolerite dykes.
• Some geologists doubt sedimentary nature, suggest igneous origin.
• Recent studies confirm sedimentary nature of many Dharwar rock terrains.
• Tendency to designate Dharwar System as Archaean, resting on gneisses of India.
• Dr. A. M. Heron identified multiple cycles of Archaean sedimentary deposits in India.
• Dharwar rocks occur as elongated synclinal outcrops among gneissic Archaeans.
• Tectonic peculiarity: preserved portions in synclinal folds, planed down by weathering.
• Rocks of Dharwar System exhibit diverse lithological characters.
• Complex includes plastic sediments, chemically precipitated, volcanic, plutonic rocks.
• Rocks show intense metamorphism, high metalliferous content.
• Ores include iron, manganese, occasionally copper, lead, gold.
• Predominantly composed of phyllites, schists, slates, hornblende-, chlorite-, haematite- and magnetite-schists, felspathic schists.
• Includes quartzites, altered volcanic rocks like rhyolites, andesites turned into hornblende-schists.
• Abundant granitic intrusions, crystalline limestones, marbles, serpentinous marbles.
• Also steatite masses, brilliantly coloured jaspers, roofing slates.
• Massive beds of iron and manganese oxides contribute to lithological diversity.
• Plutonic intrusions of Dharwar age include nepheline-syenites, elaeolite-syenite, sodalite-syenite in Rajputana.
• Dharwar granites include tourmaline-granites; other intrusives are quartz-porphyry, dunites in Salem.
• Pegmatite-veins in plutonics contain coarse crystals of muscovite, molybdenite, columbite, pitch-blende, gadolinite, beryl, tourmaline, etc.
• Crystalline limestones in Nagpur, Chhindwara from metasomatic replacement of Archaean calc-gneisses.
• Manganiferous limestones contain piedmontite, spessartite, Mn-pyroxene, -amphibole, -sphene, contributing to manganese ore.
• Flexible sandstone of Jind formed from decomposed gneisses, containing felspar grains.
• Distribution of Dharwars: Southern Deccan, Mysore, Carnatic, Chota Nagpur, Jabalpur, Nagpur, Bihar, Rewah, Hazaribagh, Aravalli region extending to Jaipur and north Gujarat.
• Dharwar rocks in Deccan exhibit hornblende-, chlorite-, talc-schists, slates, quartzite, conglomerates, and characteristic cherts.
• Synclinal outcrops with general dip towards middle of bands; associated with ortho-gneisses, schists, dioritic lavas.
• Dharwar slates show metamorphism into chiastolite-slates, phyllites, mica-schists.
• Quartz-veins in Dharwar rocks include auriferous veins supporting goldfields like Kolar in Mysore.
• Aravalli region: extensive synclinorium in Rajputana basement schistose gneisses.
• Lower Aravalli system: basal quartzites, conglomerates, shales, slates, phyllites, composite gneisses; variable metamorphism with aluminous and calcareous silicates.
• Raialo series above Aravallis with crystalline limestones, quartzites, grits, schistose rocks.
• Makrana marbles in Raialo series famous for Mogul buildings; Delhi system follows with quartzites, grits, schistose rocks.
• Delhi system regarded as Cuddapah age, includes ferruginous quartzite, slate, rhyolitic lavas in outliers like Kirana and Sangla hills.
• Metamorphism features in Rajputana’s ancient sedimentary systems show schistose and banded gneisses traced from Aravallis to unaltered shales and slates.
• Granite injections converted sedimentary rocks into banded composite gneisses resembling ortho-gneisses.
• Delhi system sediments within Aravalli synclinorium exhibit higher metamorphism and tectonic deformation than underlying Aravallis.
• Aravallis analogously correlated with Dharwars of South India, Central Provinces, Chhota Nagpur, and Mergui series of Burma.
• Champaner series in northern Gujarat includes highly metamorphosed quartzites, conglomerates, slates, and mottled marble quarried near Motipura.
• Shillong series in Assam hills comprises quartzites, slates, schists with granitic intrusions and basic interbedded traps; overlain by Cretaceous sandstones.
• Dharwarian system in Central Provinces includes Sausar series: granulites, calciphyres, dolomitic marbles, mica-sillimanite-quartz-schists, diopsidites, hornblende-schist; hosts economic manganese ores.
• Sakoli series in southern Central Provinces: less altered slates, chlorite-schists, jaspilites, haematitic quartzites, likely extension of Sausars.
• Chilpi series in Balaghat: highly disturbed slates, phyllites, quartzite, basic trap-pean intrusions; famous “marble-rocks” of Jabalpur belong to this system.
• Gondite series named for its manganese-rich rocks in Central Provinces and Bombay; includes spessartite-quartz-rock and significant manganese-ores.
• Origin of Gondite series from metamorphosed sediments originally mechanical clays, sands, chemical precipitates of manganese-oxides.
• Kodurite series in Madras Presidency: plutonic intrusions altered into manganese ore-bodies, typically in Vizianagram district.
• Singhbhum, Orissa area: Iron-ore series atop older metamorphic series; includes banded haematite-quartzites, iron-ores, shales, phyllites, quartzites, limestones, tuffs, lavas, conglomerates, schists, crystalline limestones with manganese-ore bodies.
• Iron-ore series in India is economically significant, resembling global pre-Cambrian iron formations like Lake Superior and Brazil.
• Iron oxides in Indian deposits likely marine chemical precipitates (oxides, carbonates, silicates); organic agencies not believed to aid in their formation.
• Some iron-ore deposits possibly formed by metasomatic replacement during volcanic activity.
• Ores in Singhbhum and Keonjhar occur as massive beds and lenses of ferric oxides, haematite-quartzite, jasper; associated with volcanic activity.
• Manganese-ores from Dharwar system contribute majorly to India’s production, categorized by Fermor into Kodurite, Gondite, and lateritic deposits.
• Kodurite series in Vizianagram involves meteoric alteration of manganese-silicates into manganese ores like lithomarge, chert, wad, ochres.
• Gondite series in Central Provinces, Central India, Panch Mahals metamorphosed clastic sediments yield manganese ores like braunite, hausmanite, hollandite.
• Lateritic deposits result from metasomatic replacement of Dharwar rocks by manganese-bearing solutions in Singhbhum, Jabalpur, Bellary.
• Himalayan rocks of Salkhala series in Hazara, Kohistan, Ladakh are oldest sedimentary system, associated with Central gneiss and younger Puranas.
• Salkhala series exhibits slates, phyllites, schists, quartzites, crystalline limestones; gneissification and intrusive granites complicate their identification.
• Great Himalaya range possibly represents basement of Peninsular Archaeans, influenced by Tethyan sediments in geosyncline; indicates protaxis of Himalayas.
• Archaean outcrops rare between Aravallis and Punjab Himalayas, except possible remnants in Kirana and Sangla hills buried under alluvium.
• Himalayan Dharwars known as Vaikrita series north of crystalline axis, extensively metamorphosed sedimentary rocks south, difficult to distinguish from younger sediments.
• Simla area: Jutogh series of carbonaceous slates, limestones, dolomites, quartzites, schists; metamorphosed; overlain by unconformable Simla slate series.
• Tectonics of Simla area show inverted thrust-faulting, Jutoghs thrust southward; isolated older rock outliers (“klippen”) atop Chaur and Chail mountains.
• Kashmir: Salkhala series similar to Jutoghs, carbonaceous slates, limestones, dolomites; associated with porphyritic biotite-gneiss intrusions.
• Eastern Himalayas: Doling series near Darjeeling, Sikkim, Bhutan; consists of contorted slates, chloritic and sericitic phyllites, hornblende-schists, quartzites; copper lodes present.
• Himalayan Dharwars older than Cambrian, closely associated with Archaean gneisses; no clear sedimentary origin universally accepted, debate on igneous derivation.
• Indian Archaean terrain classified into Charnockitic and non-Charnockitic regions; subdivided into provinces based on petrological characters, ore-deposits, metamorphism.
• Economic significance: Dharwar system hosts major ore-deposits (gold, manganese, iron, copper, tungsten, lead); industrial minerals (mica, corundum); rare minerals (pitchblende, columbite); gemstones (ruby, beryl, etc.); building materials (granites, marbles, slates).