Chap. III.] trichinopoly district — crystalline rocks. 29 



up. Isolated bosses and ridges of coral limestone are dotted over the 



original sea bottom of the area, and round them are banked the deposits 



of clay and sand with which, at a subsequent period, the sea became 



charged, and beneath which they are partially or wholly buried. 



In order to ensure a full appreciation of these and similar points, it will 



be necessary to premise a more detailed description 

 Crystalline rocks. 



than I have yet given of the country in the 



immediate vicinity of the Cretaceous rocks ; and I shall for this purpose 



avail myself to some extent of the results of my brother and of my 



colleagues, Messrs. King and Foote, who have principally devoted their 



attention to the examination of the Crystalline rocks. 



The Crystalline Mocks. — Trichinopoly, the principal Military Station 



of the Southern division of the Madras Presidency, 

 Trichinopoly. i • ,. 



and the chief town of the district of the same 



name, is situated at the head of the Cauvery delta near the South bank 



of that river, and a few miles below the divergence of its two main 



branches, the Cauvery and the Coleroon. The town is built on gneiss, 



a large boss of which, crowned with a pagoda, and known as Trichinopoly 



Rock, rises in the centre of the fort to a height of 236 feet above the sea. 



A few similar bosses are scattered at distant intervals over the country 



Country to South and *° *^® South, and far to the South-west are seen 



the Serumullays, one of the great island-like groups 



of hills, which, as I have already mentioned, occupy the centre and 



Western half of this part of the Peninsula. These hills, as well as the 



whole of the intervening country, consist of gneiss and other metamorphic 



rocks. 



The alluvial plain of the Cauvery opposite Trichinopoly occurs chiefly 



To North of the ^^ ^^^^ North of the river, and, including the Island 



'''"^^^^* of Seringham, which separates the two main 



branches of the stream, is not more than from 4 to 6 miles across. 



Indeed, the strictly fluviatile deposit is somewhat less than this in extent. 



