OTHER FORMATIONS. 89 



portion, as are also the laminae of quartz. The gneiss is very ferruginous. 

 In the same way, the Rasanur plateau is of about equal height, the cap 

 being of lateritic rock ; but this did not give me any such marked gneissic 

 characters. Laterite may of course haVe been deposited on the top of 

 these hills, and the ferruginous lateritoid character may have been trans- 

 mitted to the weathering gneiss below ; but it is difficult to account for 

 their caps being so much above the level of the laterite of the rest of the 

 country unless we assume that the laterite below has been denuded down 

 to its present surface from that height. Until, however, the country is 

 more closely examined as to the possible separation of the laterite and 

 lateritic deposits from the Cuddalore grits, I prefer to look on these 

 plateaus as instances of decomposed gneiss, 



The Cuddalore sandstones occur as six slightly elevated and detached 



patches separated from each other by the main 

 The Nellore plateau. . 



streams flowing to the coast. These are all so 



much alike in nearly every respect, that a description of one, for instance 

 that of Nellore, will do for the whole. This is the largest and most 

 typical plateau forming a rather elevated stretch of country overlooking 

 the gneiss plains to the west and the alluvium of the great river and the 

 coast, and it runs up into two or three low but conspicuous headlands to 

 the south-south-west of the town and at Survapali, about 1 miles to the 

 south. There is no section, nor are there any records by wells or quarries 

 to show the thickness of the rocks here ; but this can seldom be more 

 than 50 or 60 feet. The denuded surface of the subjacent gneiss is, 

 however, so irregular that the thickness varies much. Near Nellore 

 itself, or a couple of miles south-south-west, it is so thin that shallow holes 

 have been dug through it for obtaining large plates of mica from the granite 

 beneath, while only half a mile off there must be a thickness of 30 or 40 

 feet, or even more. The rocks are more or less ferruginous clays, sandy clayey 

 conglomerates, and clayey gravels and shingle. As a rule, the bottom 

 beds are pale-yellow clayey gravels and shingles, on which rests an in- 

 durated ferruginous or lateritic conglomerate, but this loses its pebbly 

 character, when of any thickness, as the surface is neared. All the wells 

 are sunk down to the bottom clayey gravel, and where they are old this 



( 177 ) 



