BRITISH POSTGLACIAL 6- RECENT DEPOSITS 399 



retired from the district to its present level. During its retreat 

 the streams and rivers busied themselves with excavating the 

 old estuarine deposits, and as they worked their way down to 

 lower levels, benches and terraces of alluvial matter were left 

 behind to mark the positions they successively occupied. 



If now we pass to the valley of the Forth, we shall there 

 meet with a similar succession of changes. The late glacial 

 deposits of the Forth form what is known as the 100-feet 

 terrace. Near Falkirk, the upper limits of this terrace are 

 marked out by the 100-feet contour line, but as we trace the 

 deposits up the valley they gradually rise to higher levels, until 

 at last they pass into ancient river-gravels. "Within this great 

 terrace, and separated from it by a steep bluff or cliff, lies a 

 second extensive flat, the upper margin of which coincides nearly 

 with the 50-feet contour line. This is the well-known Carse. 

 The deposits of which it is composed consist principally of mud, 

 silt, clay, and sand, with beds of recent sea-shells, such as 

 Cardium edule, Ostrea edulis, Mytilus edulis, Cyprina islandica, 

 Littorina litorea, Trophon clathratus, Buccinum ttndatiim, etc. 

 This wide marine flat, according to Mr. B. 1ST. Peach, is " in great 

 measure a platform cut out of the older drift deposits ; and in 

 some places, indeed, projecting ridges of the underlying rock 

 have been reached." : Layers of peat and much drifted vegetable- 

 matter, consisting of trunks, branches, and twigs of trees (birch, 

 hazel, pine, oak), occur at various levels in the Carse-deposits. 

 But none of the peat-beds, Mr. Peach tells me, indicates an 

 old land-surface. In some of the peat-beds, which are made up 

 of matted and tangled masses of sticks, twigs and branches of 

 trees, oyster-shells occur in abundance, as in a peat-bed near 

 Bridge of Allan. Eemains of the whale, 2 canoes, 3 and rude 



1 Memoirs of the Geol. Survey, Scotland, Expl. of Sheet 31 (One-inch Map), p. 54. 



2 For accounts of whale-remains got in Carse of Forth, see Edinburgh Philoso- 

 phical Journal, vol. i. p. 395 ; vol. xi. pp. 220, 415 ; Transactions of the Wernerian 

 Society, vol. iii. p. 327 ; vol. v. pp. 437, 440. 



3 Bibliotheca Topog. Britan., No. II., Part iii. p. 242 ; Beauties of Scotland, 

 vol. iii. p. 419 ; Bot. Nat. Hist. Soc. Glasgow, vol. i. p. 168 ; ii. p. 65 ; Geological 

 Magazine, vol. vi. p. 37 ; Brit. Ass. Rep., vol. xxiv. p. 80. 



