230 STRATIGRAPHICAL GEOLOGY 



pebbles of vein-quartz which, are so water-worn and rounded that 

 they resemble the pebbles of a shingle-beach. In the northern and 

 eastern part the shingle is succeeded by beds of sandstone, marl, 

 and shale which pass up into the Carboniferous Series, and these 

 beds have in several places yielded remains of fish and plants. 

 The fish belong to the genera Bothriolepis, Holoptychius, and 

 Sauripterus, and shells of Archanodon Jukesi have also been found. 

 In the extreme south and south-west these uppermost beds 

 have a different aspect. Thus in Gower the conglomerate is no 

 less than 300 feet thick and contains, besides the usual quartz 

 pebbles, some of quartzite, together with angular pieces of red 

 jasper, many of which appear to be pieces of silicified rhyolite or 

 other igneous rock. Again in Pembrokeshire, along the northern 

 outcrop and near Tenby, the group consists of quartzitic grits 

 passing up into sandstones, marls, and shales ; and at West Angle 

 Bay, south of Milford Haven, two bands of marine fossiliferons beds 

 occur in this sandstone group. The lower band commences about 

 125 feet below the line taken for the top of the group, and consists 

 of grey shales and sandstones with thin bands of limestone ; the 

 second is some 50 or 60 feet higher. Both these bands contain 

 marine shells, chiefly Lamellibranchs such as Ptychopteria damnoni- 

 ensis, Cucullcea trapezium, Curtonotus elegans, with Rhynchonella 

 laticosta and other characteristic fossils of the Marwood and Pilton 

 Beds in North Devon. Here, therefore, as pointed out by Dr. 

 Strahan, we have evidence of temporary incursions of the sea into 

 an area which had previously lain within the borders of continental 

 land, and was presumably part of a large lake-basin. 



2. Scotland 



In Scotland there are four principal areas where the Old Red 

 Sandstones are found, and in some of them they attain a much 

 greater thickness than in England. These areas are : (1) parts of 

 Berwick, Roxburgh, and of Northumberland, including the Cheviot 

 Hills ; (2) the area of the central lowlands, underlying the 

 Carboniferous rocks and coming to the surface both on the southern 

 and the northern side of the great basin ; (3) a smaller tract in 

 Argyleshire between the Firth of Lome and Loch Awe ; (4) a large 

 irregular tract in the north-east, bordering the Moray and Cromarty 

 Firths and stretching northward through the east of Sutherland to 

 Caithness and the Orkney Islands. 



It has been imagined that these four areas were distinct and 

 separate basins of deposition, at any rate during the earlier part of 

 the period ; that they were disconnected from the sea and formed 

 large inland lakes. Sir Archibald Geikie has indeed proposed 



