GENERAL DESCRIPTION. 



11 



This old marine floor is, as shall be shown later on, made up of 



gneiss, and, in one portion of the field, lower 

 Its age. , , , . - . 



Gondwana rocks (presumably ranging up into 



triassic times) ; while upper Gondwana strata (of ascertained Jurassic 

 age) are lying evenly over both of these. It is therefore clear that this 

 floor is of pre-jurassic age ; while the history of this portion of the 

 Eastern Ghats and the great river defile through them can only be con- 

 sidered to have commenced after this period. 



The different groups of rocks occurring in this field are given in 

 the following list, in which they are ranged as closely as possible with 

 the groups of the survey classification, and approximately so with the 



like sub-divisions of the European formations. 



The crystalline rocks, of which there is a large 

 area, and the sandstones of the lower Gondwana series have not yet 

 been examined in sufficient detail to admit of final description ; hence 

 they are only treated of cursorily in this Memoir, and as the floor-rocks 

 on which the other formations more particularly described are laid down. 



List of formations. 



Local groups. 



Alluvium, 

 Rdjahmundry sandstones. 



Pangadi and Kdteru Traps and 

 Inter-trappean Limestone (es- 

 tuarine). 



DudJcur Infra-trappean Beds, 

 (marine). 



Tripati sandstones (marine). 

 Rdgavapuram shales (marine). 

 Oollapili sandstones. 



Groups of Survey 

 classification. 



Approximate position in 

 European classification. 



£ £ 



Recent. 

 Cuddalore sandstones. ? Middle Eocene. 

 ? Loiver Deccan Traps. Tipper Cretaceous. 



? Lametas. Middle Cretaceous. 



Umia Beds of Cutch. Uppermost Jurassic. 



I ? Cliari Beds of Cutch, Tipper Jurassic {Ox- 

 ? Jabalpur. fordian or CalloviaJ. 



& \Rdjmahdl. 



Middle Jurassic (Ba- 

 thonian). 



Chintalpudi sandstones. 



Bezvdda gneiss. 



^ ^ Kamtlii, Damuda. 



*@ 



O 



? Upper Palaeozoic. 



Gneisses of the main or Azoic, Crystalline, 

 eastern region of the or Metamorphic 

 peninsular area. series. 



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