QUATERNARY DEPOSITS OF BRITISH ISLES BROOKS. 315 



Farther west occurs the raised beach of Portsdown Hill, near 

 Portsmouth, at nearly 100 feet above sea level, described by Prest- 

 wich (83). From here he traced the beaches along the south coast 

 into Devon, Cornwall, and South "Wales, finding them at the fol- 

 lowing levels: 



Between Blackgang and Freshwater, 80 feet. 

 . Portland Bill, 24 feet to 50 feet, rising northward. 

 Torbay, 30 feet. 

 Plymouth, 35 feet. 

 Land's End, about 20 feet. 

 Newquay, 10 to 25 feet. 

 Weston Super Mare, 25 feet. 

 South Wales. 12 ta 20 feet. 



The beach at Portland Bill consists on the western side of 

 unfossiliferous shingle, on the east, where it was more sheltered, 

 of shelly sand giving the following section : 



4. Angular rock debris ("head"), 5 feet. 



3. Loam with land shells and layers of angular debris, 6 feet. 



2. Sand, U feet. 



1. Raised beach, 3* feet. 



The shells in the sand are often very abundant, of the usual north 

 British type of this raised beach. 



In south Devon and Cornwall the beach is overlain by sands with 

 marine fossils — limpet, mussel, crab — this in turn being overlain by 

 " head." In north Devon, according to H. Dewey (81) the succes- 

 sion is: 



Bed of roimded stones (?). 



" Head." 



Cemented sand with warm temperate fauna (Helix rirgata, H. cantiana, 



BuHtmis ventricosus ) . 

 liaised beach with bowlders, probably from west Scotland. 



In Glamorgan (East Gower.) the relations of the raised beach with 

 undoubted bowlder clay were made clear by Mr. Tiddeman (85), 

 the general succession being — 



5. Recent head. 



4. Gravelly bowlder clay. 



3. Ancient head. 



2. Blown sand, often cemented into sand rock. 

 1. Raised beach, with erratics. 



This bowlder clay contains materials of northern and northeastern 

 origin, and is s]jown by the striae associated with it to have come 

 from those directions. But there occur, scattered over the hills, 

 large erratics which can only have come from the west, or from 

 the shores of the Irish Sea. These include many from St. David's 



