259 



REMARKS ON THE EVOLUTION OF THE RECENT MARINE 

 MOLLUSCAN FAUNA IN THE NEWER TERTIARY ROCKS OF 

 INDIA. 



By E. W. Ykkdexburg, F.G.S. 



Read 14th June, 1912. 



PLATE XIII. 



The diagram on PLite X I II illustrates the evolution of tlie modern marine 

 molluscan fauna in the Oligocene and Miocene of India. The materials 

 for the construction of the diagram were obtained from the researches 

 upon which the author has latterl}- been engaged in connexion with 

 Jiis surveys in the Tertiary regions of North- Western India, whicli 

 liave yielded a series of marine fossils representing several sixccessive 

 stages of the post-Eocene. The formations represented are locally 

 known under the names of Nari, Gaj, and Hinglaj. Amongst the 

 fossils whicli they contain there are a certain number of Foraminifera 

 and Mollusca identical with well-known Eui-opean forms, from which 

 it has been ascertained that the age of the Xari fauna corresponds 

 with that of the Stampian (Upper Oligocene) of Europe, that the 

 Gaj corresponds essentially with the Aquitanian, being the Indian 

 counterpart of the European Schio Beds, while the Hinglaj is 

 approximately astride of the boundary between Burdigalian and 

 Vindobonian. 



The proportions of Kecent species occurring in the successive stages 

 are as follows : — 



For the two older stages the proportion of recent Gastropoda is 

 lower than that of Kecent Lamellibranchiata. This difference is in 

 harmony with the more rapid evolution of the Gastropoda as com- 

 pared with the Lamellibranchiata. The proportion is reversed in the 

 case of the Hinglaj Beds, but the number of available forms is too 

 small to expect closely accurate statistics. 



Compared with the Tertiary faunas of European, both foraminiferal 

 and molluscan, the correspondence is close enough to allow of no 

 hesitation regarding the age of these beds, at least with regard to the 



