Geology. 181 



GEOLOGY. 



. 15. General Summary of the Geology of India. By James Calder^ 

 ^sq, — The able memoir, of which the following observations form a part, 

 was read at the Asiatic Society of Calcutta on the 19th March 1828. 



** Casting our eye over the map of India," says Mr Calder, " we are 

 struck with the grand and extensive mountain ranges which form the 

 principal boundaries. On the north we have the stupendous chain of the 

 Himalaya, extending from the confines of China to Cashmeer, and the 

 basin of the Oxus. That vast accumulation of sublime peaks, the pinna- 

 cles of our globe, is so extensive, that a plane, resting on elevations 21,000 

 feet, may be stretched, in one direction, as far as the Hindoo Cosh, for 

 upwards of 1000 miles, above which rise loftier summits, increasing in 

 height to nearly 6000 feet more. Primitive rocks alone have been found 

 to compose all that has yet been explored of the elevated portion of that 

 chain ; gneiss being, according to Captain Herbert, the predominating 

 rock, along with granite, mica, schist, hornblende, chlorite slate, and crys- 

 talline limestone. On these repose clay^slate and flinty-slate; and to- 

 wards the base we find sandstone composing the southern steps of the chain, 

 and forming the north-east barrier of the valley of the Jumna and Ganges, 

 by which, and the diluvial plains of Upper Hindoostan, this great zone is 

 separated from the mountain ranges of the Peninsula. The opposite or 

 southern boundary of this valley is of the same rock. Advancing to the 

 south, we come to three inferior mountain ranges, on which the Peninsula 

 table-land of India may be said to rest, or more properly, to which it owes 

 its peculiar form and outline. We may consider these ranges separately : 

 the western or Malabar, the eastern or Coromandel, and the central or 

 Vindya. Of these, the principal in elevation, and most remarkable in con- 

 tinuity of extent, is the western, which may be said to commence in Can- 

 deish, and runs along the Malabar coast, within a short distance of the 

 sea, in an unbroken chain to Cape Comorin, excepting where it is inter- 

 rupted near its southern extremity by the great chasm which forms the 

 valley of Coimbitoor. The direction of this chain deviates but little from 

 north and soutli, bending a little eastward towards its southern extremity. 

 Its elevation increases as it advances southward; the highest points beihg 

 probably between latitudes 10° and 15°, where the peaks of granite rise to 

 6000 feet and upwards. 



The northern extremity of this range is entirely covered by part of the 

 extensive over-lying trap formation, to be more particularly described here- 

 after ; extending in this quarter from the sea-shore of the northern Con- 

 can to a considerable distance eastward, above and beyond the ghauts, as 

 far east and south as the river Tumboodra and Nagpore, These rocks as- 

 sume all the various forms of basaltic trap, passing from the columnar (of 

 which some fine specimens are to be seen opposite to Bassein, near Bombay) 

 into the globular, tabular, porphyritic, and amygdaloidal ; the two latter 

 containing an unusual abundance and interesting variety of included mi- 

 nerals peculiar to such rocks. The landscape here exhibits all the charac- 

 teristic features of basaltic countries ; the hills rising abruptly in perpen- 

 dicular masses of a tabular form, or in mural terraces piled on each other. 



