I860.] On tlie rocks of tlie Damiida group. 357 



all quite distinct from Damiida forms. These beds were first accu- 

 rately described by Professor Oldham in a paper published in the 

 Society's Journal for the year 1853. They have since been named 

 by him the Rajmahal series. It was, however, at first thought that a 

 slight passage existed betweeD the Damiida and Rajmahal groups, a 

 view which Professor Oldham has since announced to be erroneous ; 

 the passage, if any exists, occurring in the conglomerates and grits 

 interposed between the two series. Memoirs of Geological Survey 

 of India, Yol. II. pp. 313, 325. 



The conglomerates and grits of Panchit hill, provisionally termed 

 the Upper Panchits, agree perfectly in mineral characters with those 

 "underlying the traps in the Rajmahal hills. As there is every proba- 

 bility that they occupy the same position in the general series, it is not 

 unreasonable to suppose that they are an extension of the same beds. 



A still higher group occurs in Orissa and in Central India, to 

 which the name of Mahadeva has been given. ISTo representatives of 

 it are known in Bengal, and it is possibly considerably higher in the 

 series than any of the groups above mentioned.* It is not by any 



* Professor Oldham lias suggested as probable that it is of Nummulitic (Mid- 

 dle Eocene) age. (Mem. of the Geological Survey of India, Vol. I. p. 171 and 

 Yol. II. p. 210 note), and there are doubtless arguments in favor of his sugges- 

 tion. . But the Mahadevas are in Central India overlaid unconformably by an 

 intertrappean series abounding in a shell, Physa Prinsepii, said to be very closely 

 allied to Physa Nummulitica of D'Archiac from the Nummulitic rocks of the 

 Panjab, if not identical with it. (See Hislop on the Tertiary beds and fossils of 

 Nagpur, Quarterly Journal, Geological Society, Vol. XVI. pp. 163, 164). By 

 D'Orbigny (Prodrome de Paleontologie, II. 299) Physa Prinsepii was considered 

 identical with P. Gigantea, Du Boissy, from beds near Eheims which are of the 

 lowest Eocene age, even below the plastic clay, while Nummulitic rocks are con- 

 sidered by the best authors on the subject, as, at lowest, middle Eocene. There 

 is much general similarity of facies between the fresh water (? land) shells of the 

 Bheims beds (Mem. de la Societe Geologique de France 2e. serie, Tome II. plate 6) 

 and those of the intertrappeans of Central India. The identifications of the 

 Physas are dubious, especially that of D'Orbigny, but the resemblance of the 

 facies is important. So far as this evidence goes, it tends to point out the inter- 

 trappean beds as at least as low in the series as the Nummulitics and possibly 

 lower. In this event, from the great break between the intertrappeans and the 

 Mahadevas the latter must, a fortiori, be of pre-Nutnmulitic date. But all the 

 evidence either way is of an extremely Blight description. 



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