I 



OLD CONTINENTS. 577 



color that was produced by the encasing of each individual grain of 

 sediment with a thin pellicle of peroxide of iron. 



The proof that the Old Red Sandstone was deposited in inland 

 lakes is strengthened by a similar case in well-known ancient inland 

 sheets of water, as shown by the red marls of the Miocene lakes of 

 Central France. 



It is known that in Ireland and in Scotland the Old Red Sandstone 

 consists of two divisions, upper and lower, the upper division lying 

 quite unconformably on the lower. In South Wales there are symp- 

 toms of the same kind of unconformity, for the upper beds of the Old 

 Red Sandstone gradually overlap the lower strata. But, on consider- 

 ation, this last circumstance does not appear to present any real dif- 

 ficulty with regard to the physical conditions of the period. If the 

 great hollow in which the Dead Sea lies were gradually to get filled 

 with fresh water and silted up, 1,300 feet of strata might be added 

 above the level of the present surface of the water, without taking 

 into account the depth of the sea and the deposits that have already 

 been formed ; and the upper strata all round would overlap the lower, 

 apparently much as the Old Red Sandstone strata do in Wales and 

 the adjoining counties. If the Caspian and other parts of the Asiatic 

 area of inland drainage got filled with water, the same general results 

 would follow. 



Neither does the decided unconformity between the Upper and 

 Lower Old Red Sandstones both in Ireland and in Scotland present 

 any insuperable difficulty as to the fresh-water origin of the strata. It 

 indicates only great disturbance and denudation, and a long lapse of 

 geological time unrepresented by strata between the disturbance and 

 denudation of the older beds and the deposition of the newer. Here 

 also we have a parallel case in times comparatively recent, for the 

 fresh-water Miocene strata of Switzerland and the adjacent countries 

 have been exceedingly disturbed, heaved up into mountains, and sub- 

 jected to great denudation, while at a much later geological date that 

 of to-day we have all the large fresh-water lakes that diversify the 

 country north of the Alps in the same general area. 



It is unnecessary to dilate on the well-known continental aspect 

 of a large part of the Carboniferous strata which succeed the Old Red 

 Sandstone, especially of the Coal-measures, which in the north of Eng- 

 land and in Scotland are not confined to the upper parts of the series, 

 but reach down among strata which elsewhere are only represented by 

 the marine beds of the Carboniferous Limestone. The soils (under- 

 clays), forests, and peat-mosses of the period, now beds of coal; the 

 sun-cracks, rain-pittings, bones, and footprints of Labyrinthodont Am- 

 phibia on mud now hardened into shale ; the estuarine and fresh-water 

 shells all point to vast marshes and great deltoid deposits, formed in 

 a country which underwent many changes in its physical geography, 

 and yet retained its identity throughout. 

 vol. in. 37 



