Chap. XII.] soils and superficial deposits. 195 



Patchamully hills to the Colerooii. The horizontal scale of the Section 



is -^ inch to the mile. In Fig. A the whole tract is supposed to be 



Fig. 20. Diagram Section across Trichinopoly. 



L, actual sea level; l.\ l", hypotlietical sea levels : *., s., areas of sandy soil; r., r., 



regur areas. 



submerged beneath the sea, and the only deposit forming that of marine 



sand, such as covers the sea bottom near the shore of the present coast 



line, and is in all probability mainly derived from the sediment of the 



numerous rivers which debouch into the Bay of Bengal. In Fig. B 



the country is supposed to be elevated to such an extent that the high 



tracts s. s. s. are elevated above the sea level, while shallow water still 



covers the depressions r. r. r. These latter would now have much of 



the character of the existing lagoons, the outer tracts of elevated 



ground being analogous to sand spits, and indeed it is possible that in 



some cases spits may have partially "closed the channels by which the 



depressed areas communicated with the sea. We should now have a 



mud deposit (regur) gradually formed in these, the formation ceasing 



only when either the lagoon was filled up, or when the whole area had 



been finally elevated above the sea level. 



It will be readily seen how, in the state of things supposed above, 



the red sandy soil (sea sand) would descend on the sea-ward slope 



of a ridge to a much lower level than on the inner or la2;oon-ward 



slope, as in the case illustrated in Fig. 19, page 189. In this case, 



during slow elevation, the surf would continue to break on the 



Southern slope of the ridge long after the regur deposit on its 



Northern slope had been formed, and even partly elevated above 



