other red marls, such as our Keuper beds. Solid dolomite, he goes on to say, still contains " about one-fifth per cent. of salts soluble in water, consisting of chlorides of sodium, magnesium, potassium, and calcium, and sulphate of lime. These, like those in most crystals formed from solution, must have been produced at the same time as the dolomite, and caught in some of the solution then present, which is thus indicated to have been of a briny character."
There are no solid beds of rock-salt in our Magnesian-Limestone series, though I see no reason why pseudomorphous crystals may not occur in the limestones and associated marls.
Mr. Sorby speaks of the Magnesian Limestone as having been formed in sea- water; and I presume he means ordinary open sea. I submit that it may be more probable that all our Permian magnesian limestone was chiefly or altogether formed in an inland salt lake. Under such circumstances it appears to me more likely that carbonates of lime and magnesia might have been deposited simultaneously by concentration of solutions due to evaporation ; for I cannot understand how such deposits could have taken place in an open sea, where necessarily lime and magnesia only exist in solution in very small quantities in such a large bulk of water. In the open sea, indeed, we know of the formation of beds of limestone only by means of organic agency. The occurrence of gypsum in the marly strata of the Magnesian-Limestone series helps to this conclusion. I have also observed in some of the lower strata of the Magnesian Limestone, when weathered, that they consist of a number of curious thin layers bent into a number of very small convolutions approximately fitting into each other, like a number of sheets of paper crumpled together, and conveying the impression that they are somewhat tufaceous in character, looking almost stalagmitic, as if the layers, which are unfossiliferous, had been deposited from solution, and not like ordinary organic calcareous sediment.
In an elaborate disquisition on dolomites, in two lectures, Dr. Percy concludes with the following words : — " That dolomite has been formed by the agency of liquids under very ordinary conditions, I have little doubt will be hereafter fully established by direct and indisputable chemical evidence" *. In the ' Geology of Canada ' (Logan) Dr. Sterry Hunt has given the results of his chemical investigations bearing on geology, in chapters 17-20. At pp. 575-6 he discusses the subject of dolomites. The passages are too long for quotation ; but after explaining various natural processes by which he conceives that mixed carbonates of lime and magnesia may be deposited from solution in salt water, he concludes that " these reactions require inland seas, or basins cut off from communication with the ocean, while, on the other hand, the conditions of the production of carbonate of lime are everywhere found." The chemical arguments are not what first led me to suspect that the Permian magnesian limestone was deposited in an inland salt sea from solution, though I soon after began to entertain the idea, and to search for evidence on the point. It is satisfactory to find that eminent chemists take this view with
- Swiney Lectures, 1864, 'The Chemical News,' p. 89.
