Prof. A. C. Ramsay on the Red Rocks of England. 229 



shells a change in the condition of the waters. The fish of the Old 

 Red Sandstone also indicate a change of condition of a geographical 

 kind. 



The circumstances which marked the passage of Silurian into Old 

 Red Sandstone were as follows : — Pirst, shallowing of the sea, so 

 that the area changed into fresh and brackish lagoons, afterwards* 

 converted into great freshwater lakes. At the present day marine 

 species are occasionally found living in fresh water, as for example 

 in the Swedish lakes. The same may have been partly the case in the 

 Old Red Sandstone period. The Old Red Sandstone waters at their 

 beginning are comparable^to the Black Sea, now steadily freshening — 

 or the Caspian, once united to the North Sea, if by a change of 

 amount of rainfall and evaporation it freshened by degrees, and 

 finally became a freshwater lake. 



The Permian strata, to a great extent, consist of red sandstones 

 and marls in the greater part of England ; and the Magnesian Lime- 

 stone of the north of England is also in less degree associated with 

 red marls. These do not occur in the same districts of England, 

 excepting in Lancashire, where a few beds of Magnesian Limestone 

 are interstratified with the marls. The sandstones and marls being 

 red, the colouring-matter is considered to be due to peroxide of iron, 

 possibly precipitated from carbonate of iron, introduced in solution 

 into the waters. 



Land-plants are found in some of the Permian beds, showing the 

 neighbourhood of land. No mollusca are found in most of the red 

 beds, except a brachiopod in Warwickshire, and a few other genera 

 in Lancashire, in marls associated with thin bands of Magnesian 

 Limestone. 



The traces of amphibians are like those found in the Keuper Sand- 

 stone, viz. Dasyceps Bucldandi, and Labyrinthodont footprints in 

 the Yale of Eden and at Corncockle Moor, printed on damp surfaces, 

 dried in the sun, and afterwards flooded in a way common in salt 

 lakes. Pseudomorphous crystals of salt and gypsum help to this 

 conclusion. 



The molluscous fauna of Lancashire, small in number, in this 

 respect resembles the fauna of the Caspian Sea. The fauna of the 

 Magnesian Limestone of the east of England is more numerous, 

 comprising thirty-five genera and seventy-six species, but wonder- 

 fully restricted when compared with the Carboniferous fauna. The 

 specimens are generally dwarfed in aspect, and in their poverty 

 may be compared to the Caspian fauna of the present day. Some 

 of the fish of the Marl-Slate have strong affinities to carboniferous 

 genera, which may be supposed to have lived in shallow lagoons, 

 bordered by peaty flats ; and the reptiles lately described by Messrs. 

 Howse and Hancock have terrestrial affinities. 



Besides the poorness of the Mollusca, the Magnesian Limestone 

 seems to afford other hints that it was deposited in an inland salt 

 lake subject to evaporation. Gypsum is common in the interstra- 

 tified marls. In the open sea limestone is only formed by organic 

 agency ; for lime, in solution, only exists in small quantities in such 

 a bulk of water ; but iu inland salt lakes carbonates of lime and 



