Geological Society of London. 227 



Geological Society of London. — I. March 8, 1871. — Josepli 

 Prestwich, Esq., F.K.S., President, in tlie Chair, The following 

 communication was read : — 1. " On the Eed Eocks of England of 

 older date than the Trias." By Prof. A. C. Eamsay, LL.D., F.E.S., 

 V.P.G.S. 



The author stated that the red colour of the Triassic beds is due 

 to peroxide of iron, which encrusts the sedimentary grains as a thin 

 pellicle. This could not have heen deposited in an open sea, but 

 rather in an inland salt lake or lakes. The peroxide of iron, which 

 stains the Permian, Old Eed Sandstone and Cambrian rocks, is be- 

 lieved by the author to have been deposited in the same manner, in 

 inland waters, salt or fresh. 



Agreeing with Mr. Godwin-Austen, the Old Eed Sandstone was of 

 Lacustrine origin. The absence of marine shells helps to this con- 

 clusion. The fish do not contradict it, for some of their nearest 

 living congeners live in African and American rivers. 



The life of the Upper Silurian deposits of Wales and the adjoining 

 districts continued in full force up to the passage-beds, which mark 

 the change from Silurian to Old Eed Sandstone. Li these transition 

 strata, genera, species, and individuals are often few, and dwarfed in 

 form. Near Ludlow and May HiU the uppermost Silurian strata 

 contaia seeds and fragments of land-plants, indicating the neighbour- . 

 hood of land, and the poverty of numbers and the small size of the 

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

 Eed Sandstone also indicate a change of condition of a geographical 

 kind. 



The circumstances which mark the passage of Silurian into Old 

 Eed Sandstone were as follows; — ^First, shallowing of the sea, so 

 that the area changed into fresh and brackish lagoons, afterwards 

 converted into great fresh- water 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 the case in the Old 

 Eed Sandstone period. The Old Eed 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 fresh-water 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. 



