Volume 1

A manual of the geology of India / chiefly compiled from the observations of the Geological Survey.

Date:
1879-1887
Catalogue details

Licence: Public Domain Mark

Credit: A manual of the geology of India / chiefly compiled from the observations of the Geological Survey. Source: Wellcome Collection.

    530/554 (page 424)
    The site of this boring was at the Inland Custom-house, three- quarters of a mile from the sea. Beneath the depth mentioned crystal- line rocks occurred. It is probable that the alluvium is in most places thicker than at Madras, but nothing more has been ascertained on this head. The subfossil shells near Madras are so abundant in places that they have been collected for burning into lime. Farther south also, near Porto Novo, in the lower valley of the Vellaur,1 a bed of estuarine shells is found above the present flood-level of the river, and consequently at a considerable height above the sea. Similar deposits of shells have also been noticed near Cuddalore and Tanjore.2 Another place where estuarine shells have been observed is close to the Chilka lake in Southern Orissa. The forms found were Cy there a casta and Area granosa, and the deposit containing the shells is now at an elevation of from 20 to 30 feet above the level of the highest tides. Alluvium of the west coast of India.—The differences in physi- cal character between the east and west coast of India have already been noticed. Along the western shore of the Peninsula there is no such continuous plain of alluvium as on the east coast; the ground between the Sahyadri range and the sea, where not hilly, consists generally of a gentle slope towards the coast, composed of rock, covered in many places by laterite. The coast itself is rocky in parts, and the alluvial deposits are chiefly confined to the neighbourhood of the small streams, which run from the Western Ghats to the sea, or of the backwaters or lagoons which have been cut off by banks of sand along the coast. The backwaters are of considerable extent in Travancore and Malabar, but they are wanting farther north and on the coast of the Bombay Presidency ; the alluvial valleys between the hills are unimportant south of Bombay itself, although they gradually increase in extent to the northward. Bombay-—Alluvial plains, evidently of comparatively recent forma- tion, connect the hills of Bombay and Salsette Island, a few creeks alone remaining to shew the position of the marine channels which formerly existed. Farther north these plains gradually increase in extent, until they merge into the alluvial flat of Guzerat. At Bombay the alluvial deposits3 consist of blue and yellowish-brown clay ; the former varies in thickness from a few inches to several feet, its upper surface being at present about a foot or two below high-water level; it is very salt, and contains small grains and nodules of kankar, and 1 II. F. Blanford : Mem. G. S. I., IV, p. 192. 2 King and Foote : ib., p. (254.) 2 Buist: Trans. Bombay Geo. Soc., X, p. 181;—Carter: Jour. Bombay Br. R. A.&., IV,