264 NEOZOIC TIME. [CHAP. XIII. 



the valley of the Earn, and to Luncarty, above Perth, in 

 that of the Tay, passing ultimately into gravels of tor- 

 rential origin, which descend from the valleys of the Gram- 

 pian Hills. To the same stage belong the fossiliferous 

 brick-clays of the Forth and Clyde valleys. 



Post-Glacial Deposits. These consist of raised beaches 

 and clay-flats lying between low-water mark and the con- 

 tour of 50 feet above mean sea-level. The most important 

 and widely distributed deposit is that known as the 

 Carse-clay, or the estuarine clay which forms the elevated 

 alluvial levels which are known as Carse-lands. The 

 surface of these levels near the sea-bord is from 25 

 to 30 feet above the sea, and their borders coincide 

 with a line of raised sea-beach at the same level. When 

 traced inland up the valleys their surface rises gra- 

 dually to a level of about 45 or 50 feet, at which level 

 they pass into freshwater alluvium, while their lateral 

 portions thin off against the raised beach, which occupies 

 the 50-foot contour. The clays and silts contain marine 

 shells, of which Scrobicularia piperata is one of the com- 

 monest ; but at or near the base there is frequently a bed 

 of peat in which trunks and rooted stools of trees occur, 

 and in some places this peat bed passes below the mean 

 level of the sea and is then called a submarine forest-bed. 

 The modern river- valley is excavated through the Carse- 

 clays, and contains fluviatile deposits of the ordinary 

 recent freshwater type. 



In some cases, as in that of the Tay, 1 there are river- 

 gravels beneath the Peat and Carse-clay, and these, as well 

 as the submarine extension of the Peat, show that the land 

 stood at a higher level and had a farther seaward exten- 

 sion than it has now. The Carse-clay marks a period 



1 J. Geikie in " Prehistoric Europe," p. 316, and Jamieson. " Quart. 

 Journ. Geol. Soc.," vol. xxi. p. 184. 



