306 



GEOLOGICAL SURVEY 



tives of the Rajmahal beds near Madras, and after much close 

 work over a difficult country — difficult because of the great 

 want of clear sections — found them to be provisionally divisi- 

 ble into two groups, the Sattavedu and Sripermatur groups. 

 These plant beds or Rajmahal beds occur in scattered patches 

 fringing the higher grounds and resting directly on the gneiss 

 and being overlaid themselves by the younger cretaceous rocks, 

 or the Cuddalore sandstones and lateritic rocks where the 

 cretaceous rocks are absent. In some cases all three are 

 absent, and then the plant beds are overlaid by the recent 

 alluvia, whether fluvestile or marine. 



There is considerable petrological difference, as might be 

 expected, between the more widely separated patches of these 

 Upper Grondwana rocks ; thus the beds below the cretaceous 

 rocks in Trichinopoly District are most friable sandy shales, 

 the fossil plants from which can hardly be preserved, so 

 slight is the consistency of the matrix. In the vicinity of 

 Sripermatur the shales, which here also predominate, are mostly 

 hard, often indeed almost porcellanic in texture, and the 

 vegetable remains they enclose are preserved with wonderful 

 perfection and durability, nothing short of great violence 

 sufficing to obliterate them. Still further north in the 

 Alicoor hills the shales and soft unctuous clays are associ- 

 ated with uncompacted conglomerates of extraordinary 

 coarseness. Some of these are so excessively coarse that it is 

 extremely difficult to understand how they came to be formed, 

 glacial action not being an admissible factor in a climate in 

 which cycadeous plants abounded. The lower or Sripermatur 

 group consists of shales with a few not very important 

 sandstones overlaid by clays and uncompacted conglomerates 

 (in the Alicoor hills) of various degrees of coarseness. This 

 group is overlaid by a series of enormously coarse, hard, 

 slightly ferruginous conglomerates with a few beds of sand- 

 stone. The name " Sattavedu group ' ; has been given to these, 



