244 PROCEEDINGS 01-' THE GEOLOGICAL SCCIETT. [Mar. 8, 



sent, owing to the uncongenial quality of the water, many of the 

 Black-sea shells are strangely distorted, as shown by Edward Forbes. 



Or if we take the Caspian alone, as it now stands, as an example, 

 we have a salt inland sea which, according to accepted views, was 

 once united to the North Sea and, possibly, at the same time to the 

 Black Sea, as shown by the Aralo-Caspian deposits, at a time when the 

 Bosphorus was still closed. Changes in physical geography have 

 taken place of such a nature that the Caspian is now disunited from 

 the ocean, while its waters are still inhabited by a poor and dwarfed 

 marine molluscan fauna, and by seals. If by increase of rainfall the 

 Caspian became freshened, evaporation not being equal to supply, it 

 would by and by, after reaching the point of overflow, be converted 

 into a great freshwater lake, larger in extent than the whole area 

 now occupied by the Old Eed Sandstone of Europe *. It is even 

 conceivable that the great area of inland drainage of Central Asia, 

 now holding many salt lakes, might in the same manner be so changed 

 that all its lakes would become fresh and widened in extent, thus 

 occupying areas many times as large in extent as all the known 

 European Old Red Sandstone. Under these circumstances, in the 

 Caspian area we should have a passage more or less gradual from 

 marine to freshwater conditions, such as I conceive to have marked 

 the advent of the Old Red Sandstone. When the whole area was 

 fairly isolated from the sea, the sediments might by degrees get 

 into a condition to be coloured red in the manner previously men- 

 tioned. We have a case in point in an old inland sheet of water, as 

 shown by the red marls of the Miocene lakes of Central France. In 

 certain of the strata of the Old Red Sandstone, especially in the upper 

 beds, the colour has been here and there discharged in irregular 

 patches, probably through the reducing action of organic matter, 

 and the percolation of water containing carbonic acid. 



Mr. Jukes divided the Old Red Sandstone of Ireland into two 

 portions. The lower series is conformable with and adheres to the 

 Upper Silurian strata. The upper series lies quite unconformably 

 on the lower, and adheres to and is conformable with the Carboni- 

 ferous strata. In Wales and the adjoining counties no such uncon- 

 formity has been clearly made out and mapped, though Sir Henry 

 De la Beche pointed out that such a division may exist, as shown by 

 the overlap of the upper strata across the lower^ proceeding west- 

 ward from Breconshire into Carmarthenshire and Pembrokeshire. 

 However this may be, the thickness of the Old Red Sandstone is 

 often very great ; and this to some minds, taken perhaps in conjunc- 

 tion with unconformity, may present a difficulty to the acceptance 

 of my view. In South Wales and Herefordshire the formation is 

 from 2000 to 7000 or 8000 feet thick, as determined by my mea- 

 surements carefully levelled in 1843. But on consideration these 

 circumstances do not appear to present any real difficulty. If the great 

 hoUow in which the Dead Sea lies were gradually to get filled 

 with fresh water and silted up, 1300 feet would be added above the 

 level of the present surface, Avithout taking into account the depth 

 * Exclusiye of marine Devonian rocks. 



