beds, which must have grown quietly at the surface, alternating with deposits of gravel, sand, and clay. The thickness of the delta deposit is unknown; 481 feet was proved at the bore hole, but probably this represents only a very small part of the deposit. Outside the delta, in the Bay of Bengal, is a deep depression known as the 'swatch of no ground'; all around it the soundings give only 5 to 10 fathoms, but they very rapidly deepen to over 300 fathoms. The sediment seems to be carried away from this hole by the set of the currents; so that it has remained free from silt whilst the neighbouring sea-bottom has gradually been filled up. If so, the thickness of the alluvium is at least 1800 feet, and may be much more.

history.

The Indo-Gangetic plain dates back to Eocene times; the Its geoorigin of the Himálayas may be referred to the same period. logical Numerous minor disturbances occurred in the area which is now Northern India during Palæozoic and Secondary times, but the great disturbance which has resulted in the formation of the existing chain of the Himálayas took place after the deposition of the Eocene beds. Disturbances even greater in amount occurred after the deposition of the Pliocene beds. The Eocenes of the sub-Himálayan range were deposited upon uncontorted Palæozoic rocks, but the whole has since been violently contorted and disturbed. There are some indications that the disturbing forces were more severe to the eastward during middle Tertiary times, and that the main action to the westward was of later date. It seems highly probable that the elevation of the mountain ranges and the depression of the Indo-Gangetic plain were closely related. This view gains some support from a glance at the map, where we see that the curves of the great mountain chains are strictly followed by those of the great alluvial plain. Probably both are due to almost contemporary movements of the earth's crust; these movements, though now of vastly diminished intensity, have not wholly ceased. The alluvial deposits prove depression in quite recent geological times; and within the Himalayan region earthquakes are still common, whilst in Peninsular India they are rare.

India.

Peninsular India.-The oldest rocks here consist of gneiss, Peninsular in three tracts: - throughout a very large part of Bengal and Madras, extending to Ceylon; among the Aravalli ranges; and in Bundelkhand. Of these formations, the gneiss of Bundelkhand is known to be the oldest, because the oldest Transition rocks rest upon it; whereas the same Transition

rocks.

rocks are altered and intersected by granitic dykes which proceed from the gneiss of the other tracts. The Transition Vindhyan rocks are of great but unknown age. The Vindhyán rocks which succeed them are of very old Palæozoic age, perhaps pre-Silurian. Yet long before the earliest Vindhyán rocks were laid down, the Transition rocks had been altered and contorted. In more recent times there have been local disturbances, and large faults have in places been found; but the greater part of the Peninsular rocks are only slightly disturbed, and the most recent of the great and wide-spread earth movements of this region date back to pre-Vindhyán times. The Vindhyán series are generally sharply marked off from older rocks; although in the Godávari valley there is no welldefined line between these and the Transition rocks.

Lower

Vindhyáns.

Upper Vindhyáns.

Gondwána series.

The Vindhyan beds are divided into two groups. The lower, with an estimated thickness of only 2000 feet, or slightly more, cover a large area,-extending, with but little change of character, from the Son valley in one direction to Cuddapah, and in a diverging line to near Bijapur-in each case a distance of over 700 miles. The upper Vindhyáns cover a much smaller area, but attain a thickness of about 12,000 feet. The Vindhyáns are well-stratified beds of sandstone and shale, with some limestones. As yet they have yielded no trace of fossils, and their exact age is consequently unknown. So far as the evidence goes, it appears probable that they are of very ancient Palæozoic age, perhaps pre-Silurian. The total absence of fossils is a remarkable fact, and one for which it is difficult to account, as the beds are for the most part quite unaltered. Even if they are entirely of fresh-water origin, we should expect that some traces of life from the waters or neighbouring land would be found.

The Gondwana series is in many respects the most interesting and important of the Indian Peninsula. The beds are almost entirely of fresh-water origin. Many subdivisions have been made, but here we need only note the main division into two great groups :-Lower Gondwánas, 13,000 feet thick; Upper Gondwánas, 11,000 feet thick. The series is mainly confined to the area of country between the Narbadá and the Son on the north and the Krishna on the south; but the western part of this region is in great part covered by newer beds. The lowest Gondwánas are very constant in character, wherever they are found; the upper numbers of the lower division show more variation, and this divergence of character in different Districts becomes more

marked in the Upper Gondwána series.

Disturbances have occurred in the lower series before the formation of the upper.

fossils.

The Gondwána beds contain fossils which are of very great Gondwana interest. In large part these consist of plants which grew near the margins of the old rivers, were carried down by floods, and deposited in the alluvial plains, deltas, and estuarine areas of the old Gondwána period. So vast was the time occupied by the deposition of the Gondwána beds, that great changes in physical geography and in the vegetation repeatedly occurred. The plants of the Lower Gondwánas consist chiefly of acrogens (Equisetaceæ and ferns) and gymnogens (cycads and conifers), the former being the more abundant. The same classes of plants occur in the Upper Gondwanas; but there the proportions are reversed, the conifers, and still more the cycads, being more numerous than the ferns, whilst the Equisetaceæ are but sparingly found. But even within the limits of the Lower Gondwána series there are great diversities of vegetation, three distinct floras occurring in the three great divisions of that formation. In many respects the flora of the highest of these three divisions (the Pánchet group) is more Pánchet nearly related to that of the Upper Gondwánas than it is to group. the other Lower Gondwána floras.

One of the most interesting facts in the history of the Tálcher Gondwána series is the occurrence near the base (in the Tálcher group. group) of large striated boulders in a fine mud or silt, the boulders in one place resting upon rock (of Vindhyán age) which is also striated. There seems good reason for believing that these beds are the result of ice-action. They probably nearly coincide in age with the Permian beds of Western Europe, in which Professor Ramsay long since discovered evidence of glaciation. But the remarkable fact is that this old ice-action occurred within the tropics, and probably at no very great height above the sea.

series and

coal-fields.

The Damodar series, the middle division of the Lower Gond- Damodar wánas, is the chief source of coal in Peninsular India, yielding more of that mineral than all other formations taken together. The Karharbári group is the only other coal-bearing formation of any value. The Damodars are 8400 feet thick in the Ráníganj coal-field, and about 10,000 feet thick in the Sátpura basin. They consist of three divisions; coal occurs in the upper and lower, ironstone (without coal) in the middle division. The Rániganj coal-field is the most important in India. So far as Ráníganj is yet known, it covers an area of about 500 square miles, running about 18 miles from north to south, and about 39

coal-field.

Rániganj coalseams.

seams.

miles from east to west; but it extends farther to the east under the laterite and alluvium. It is traversed by the Dámodar river, together with the road from Calcutta to Benares and the East Indian Railway. From its situation and importance, this coal-field is better known than any other in India. Much has been learnt concerning it since the last examination by the Geological Survey, especially from the recent reports by Mr. H. Bauermann.

The upper or Ráníganj series has eleven seams, with a total thickness of 120 feet, in the eastern district, and thirteen seams, 100 feet thick, in the western district. The average thickness of the seams worked is from 12 to 18 feet, but occasionally a seam reaches a great thickness — 20 to So Barákhar feet. The lower or Barákhar series (2000 feet thick) contains four seams, of a total thickness of 69 feet. Compared with English coals, those of this coal-field are of a poor quality; they contain much ash, and are generally non-coking. The seams of the lower series are the best, and some of these at Sánktoria, near the Barákhar river, are fairly good for coke and gas. The best coal in India is in the small coal-field at bári coal- Karharbári. The beds there are lower in the series than those of the Ráníganj field; they belong to the upper part of the Tálcher group, the lowest of the Gondwána series. The Karharbári coal-beds cover an area of about 11 square miles; and have three seams, varying from 9 to 33 feet thick. The lowest seam is the best, and it is nearly as good as English steam coal. This coal-field, now largely worked, is the property of the East Indian Railway, which is thus supplied with fuel at a cheaper rate than any other railway in the world. Indian coal usually contains phosphoric acid, which greatly lessens its value for iron-smelting.1

Karhar

field.

Dámodar iron-stone.

The Dámodar series, which, as we have seen, is the chief source of coal in India, is also one of the most important sources of iron. The ore occurs in the middle division, coal in the highest and lowest. The ore is partly a clay ironstone, like that occurring in the coal-measures of England, partly an oxide of iron or hæmatite. It generally contains phosphorus, which prevents its use in the preparation of the finer qualities of steel. A similar difficulty attends the use of the Cleveland ore of North Yorkshire. Experiments have been in progress for years in search of a process which shall, in an 1 The economic aspects of Indian coal have been dealt with ante, pp. 487, 488. For full accounts of the Indian coal-fields, see articles RANIGANJ, KARHARBARI, etc., in the Imperial Gazetteer of India, vols. viii. and v.

economical manner, obtain iron from Cleveland ore free from phosphorus, latterly, it is hoped, with some success. If this be so, India will be a great gainer. Excellent iron-ore occurs in the metamorphic rocks south of the Dámodar river. Laterite (see below) is sometimes used as ore. It is very earthy, with a low percentage of metal; but it contains only a comparatively small proportion of phosphorus.1

The want of limestone for flux, within easy reach, is generally a great drawback as regards iron-smelting in India. Kankar or ghutin (concretionary carbonate of lime) is col- Kankar. lected for this purpose from the river beds and alluvial deposits. It sometimes contains as much as 70 per cent. of carbonate of lime; but generally the proportion is much less, and the fluxing value proportionally diminished. The real difficulty in India is to find the ore, the fuel, and the flux, in sufficiently close proximity to yield a profit.

The enormous mass of basaltic rock known as the Deccan Deccan trap, is of great importance in the geological structure of the trap. Indian Peninsula. It now covers an area of about 200,000 square miles, and probably extended in former times over a much wider area. Where thickest, the traps are at least 6000 feet in depth. They form the most striking physical features of the country, many of the most prominent hill ranges being the denuded edges of the basaltic flows. The great volcanic outbursts which produced this trap commenced in the Cretaceous period, and lasted into the Eocene period.

Laterite is a ferruginous and argillaceous rock, varying from Laterite; 30 to 200 feet thick, which often occurs over the trap area, but is also found in other tracts. As a rule, it makes rather barren land; it is highly porous, and the rain rapidly sinks into it. Laterite may be roughly divided into two kinds, high-level and low-level laterite. The former, which covers a high-level; large area of the high basaltic plains, is believed by Mr. R. B. Foote to be very frequently the product of decomposition of the trap, and to have been thus formed in the place where it is now found. Sometimes the high-level laterite overlies gneiss or other rocks; and in these cases it has probably been transported. The low-level laterite is generally more low-leve! sandy in character, and is often associated with gravels. In most cases this has clearly been carried down to its present position, probably largely by subaerial action, aided by rains and streams. Possibly in some cases it has been spread out along the coasts by marine action. The low-level laterite 1 For the economic aspects of Indian iron, see ante, pp. 486, 487.