INTRODUCTION. 13 



of the Dharwars preserved the time interval is greater than that 

 covered by any younger " group." Some of the gneissose granites 

 are younger, others are older than some Dharwars. The important 

 point to notice is that while among the Dharwars, gneisses and 

 schists, only divisions of local value can be made out according to 

 time and order of succession, there is a widespread and great 

 unconformity between these foliated rocks as a whole and the non- 

 foliated Purana systems — Cuddapahs, Kaladgis, Bhimas, Kurnools 

 and Vindhyans. This great unconformity thus forms a natural group 

 limit in India as in Canada and South Africa, and all three areas 

 having escaped later folding movements show still clearly preserved 

 the distinction between the groups, Archaean and Purana. 1 



The next great division line selected by Holland was taken to 

 be about equivalent to the Middle or Upper Carboniferous of 

 Europe — the basement beds of the Gondwana system, those below 

 the Productus Limestones of the Salt Eange and the unconformity 

 of similar age in the Himalaya. The rocks below this break formed 

 the proposed Dravidian groitf, while those above were linked together 

 to form the Aryan group. 



In 1907 Mr. E. W. Vredenburg published " A Summary of the 

 Geology of India," in which he introduced certain modifications of 

 previous classifications. He separated the Dharwars from the 

 Archaean gneisses and schists, not on mere lithological grounds, 

 a3 in the case of Holland's classification, but on account of their 

 supposed younger age. The reasons for linking the Dharwars 

 with the gneisses and schists in one group have, however, been indi- 

 cated above and are more fully discussed below under the headings 

 Archaean, Dharwar and Purana. The Vindhyans are by Vreden- 

 burg distributed through the Cambrian system, apparently on the 

 ground of a rough lithological correspondence between them and 

 the fossiliferous Cambrian beds of the Salt Range. A much greater 

 degree of precision in correlating isolated occurrences of the Creta- 

 ceous and Tertiary stages is attempted in consequence of recent 

 palaeontological work. In the " Summary," as in the papers 

 cited, it is insisted 2 that the gradual transition of Cretaceous 



1 Dr. L. L. Fermor (Bee, Geol. Sun., Ind., Vol. XLI, 292, 1912) in recording the 

 discussion at the Stockholm (1910) meeting of the International Geological Congress 

 confirms Holland's classification and proposes to extend it to other similar areas. 



2 Fuller discussions of these results will be found in separate papers published in Rec, 

 Geol. Surv., Ind., Vol. XXXIV, parts 2, 3, and 4 ; Vol. XXXV, parts I and 2 ; Vol. 

 XXXVI, parts 2, 3, and 4 ; Vol. XXXVIII, parts 2, 3, and 4. Vredenburg's results are 

 not always in agreement with those of Pilgrim, who has mainly studied the fresh-water 

 fossiferona deposits (cf. Rec, Geol. Surv., Ind., Vol. XL, part 3). 



