Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/388

 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 Red Marl &c. On referring to Sir William 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 satisfaction to find myself so far supported by authorities so eminent, though neither of them mentions the red colour as a necessary concomitant 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 Red 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.

Discussion.

Prof. Huxley 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 Ceratodus, but which, in many characters, was very similar to Dipterus, and in some respects resembled Phaneropleuron. In other respects it was connected with Lepidosiren. It was about to be fully described by Dr. Gunther. 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 mammalian remains in earlier formations than those in which they are at present known. He did not so cordially agree with his views as