Memoirs of the Geological Survey of India . ion of the plains and the lagoon origin of the regurbeing proved, that of the red sandy soil is readily suggested. It is amarine sand, such as accumulates (nowhere probably to any greatthickness) on the sea shore at the present day. The great probabi-lity at all events of such an origin is seen when we remember its geo-graphical relations to the regur as regards elevation, and considerwhat would be the condition of tracts slightly above the average levelof the country during a course of slow upheaval. The accompanyingfigures (Fig. 20) are diagram sec
Memoirs of the Geological Survey of India . ion of the plains and the lagoon origin of the regurbeing proved, that of the red sandy soil is readily suggested. It is amarine sand, such as accumulates (nowhere probably to any greatthickness) on the sea shore at the present day. The great probabi-lity at all events of such an origin is seen when we remember its geo-graphical relations to the regur as regards elevation, and considerwhat would be the condition of tracts slightly above the average levelof the country during a course of slow upheaval. The accompanyingfigures (Fig. 20) are diagram sections across Trichinopoly from the * These were mapped by Messrs. King and Foote, but I saw them myself subsequentljaud am therefore in a position to speak as to their real character from personal observation. 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 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 eithe
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