CHAP. V.] DEVONIAN PERIOD. 57 



The Upper Old Eed Sandstone proper borders the Car- 

 boniferous areas of Gloucester, Monmouth, and Glamorgan, 

 and stretches westward into Carmarthen and Pembroke, 

 overlapping both the underlying groups and the Silurian 

 rocks, till it rests directly on the Ordovician between Car- 

 marthen and Narberth. The beds consist of red and white 

 conglomerates at the base, succeeded by red marls, above 

 which are red and yellow sandstones with fish and plant 

 remains. It has been supposed that these strata are of 

 lacustrine origin, but no freshwater mollusca have yet 

 been found in them, while Serpulce and the Pteropod Conu- 

 laria are said to occur in them, so that there seems much 

 more reason to regard them as marine. Southward they 

 are found in the Mendip Hills, and they were doubtless 

 continuous with the Pickwell Down Sandstones of North 

 Devon and the Cockington Beds of South Devon. To the 

 northward they are found in the Clee Hills of Shropshire, 

 but as they do not recur beneath the Carboniferous rocks 

 of the neighbouring coalfields, that seems to have been 

 nearly the limit of their original northward extension. 



They may be represented in Anglesey, where there are 

 600 feet of red sandstone and conglomerate below the 

 Carboniferous Limestone, but neither here nor in Denbigh 

 and Flint is there any definite band of shale between the 

 sandstones and the limestones, so that it seems more pro- 

 bable that the former are shore beds of the age of the 

 limestone, and therefore newer than the true Upper Old 

 Eed Sandstone. 



The same is the case in the north of England and in 

 the south of Scotland, where there is always a group of red 

 sandstones at the base of the Carboniferous system, and in 

 Scotland these are sometimes 2,000 feet thick, but they 

 occasionally contain beds of red limestone with Carboni- 

 ferous fossils. 



In the east of Scotland, however, there are older beds 



