254 PBOCEEDINGS OF THE GEOLOGICAL SOCIETT. [Mar. 8, 



between Palaeozoic and later times begin to be discovered even 

 now. 



Note. — After the foregoing paper was written I recollected certain 

 red Silurian rocks which I had seen in America, known as the 

 Onondaga Salt-Group, which contain gypsum, salt, and magnesian 

 limestone. I at once surmised that their origin must have been 

 similar to that of the red rocks of Britain mentioned in this and my 

 previous paper on the New Eed Marl &c. On referring to Sir 

 WOHam Logan's ' Geology of Canada ' (1863), I find, p. 346, that he 

 considers that the gypsum, " hopper-shaped moulds of salt," and 

 other signs show that these rocks, part of which are red marl, 

 " were deposited from waters concentrated by evaporation." 



Professor Dana in his 'Manual of Geology' (1863), p. 249, speaking 

 of the same strata, says " that the region which in the preceding 

 period was covered with sea and alive with Corals, Crinoids, 

 Mollusks, and Trilobites, making the Niagara limestone, had now 

 become an interior shallow basin, mostly shut off from the ocean, 

 where the salt waters of the sea, which were spread over the area 

 at intervals — intervals of days or months it may be, — evaporated, 

 and deposited their salt over the clayey bottoms," &c. It is a satis- 

 faction to find myself so far supported by authorities so eminent, 

 though neither of them mentions the red colour as a necessary con- 

 comitant of the inland-water condition of the Onondaga deposits. 



Principal Dawson, of Montreal, has also published several papers 

 in the Journal of this Society, partly illustrative of the Red Rocks 

 of Nova Scotia. In one of these, " On the Colouring-matter of Eed 

 Sandstones and of Greyish and White Beds associated with them " 

 (vol. V. p. 25, 1848), he shows that the colouring matter is peroxide 

 of iron in a fine state of division, and that it is " like a chemical 

 precipitate," and also that the gypsum in these strata is a chemical 

 deposit : and he considers that these and other phenomena may " in 

 some cases serve to distinguish marine from freshwater deposits." 

 He does not, however, argue the case precisely on the grounds 

 advocated in this paper. 



DlSCIJSSIOK^. 



Prof. HtrxLET was pleased to find that the author, on physical 

 grounds, extended some views which he himself had, from other 

 reasons, brought before the Society. He mentioned that there had 

 lately been found in the fresh waters of Australia a remarkable 

 fish, which had been considered to be a Ce^^atodus, but which, in 

 many characters, was very similar to Dipterus, and in some respects 

 resembled Phmieroj)leu7'on. In other respects it was connected 

 with Le^idosiren. It was about to be fully described by Dr. Giin- 

 ther. The fact that this remarkable fish inhabits fresh water, 

 he thought, corroborated Prof. Ramsay's argument. He agreed 

 with the author as to his views respecting the terrestrial fauna 

 of ancient times, and was quite prepared for the discovery of mam- 

 maHan remains in earlier formations than those in which they are 

 at present known. He did not so cordially agree with his views as 



