THE DRIFT OR GLACIAL FORMATION OF THE CLYDE 



DRAINAGE AREA. 



BY JOHN SMITH. 



THE DRIFT BELOW SEA-LEVEL. 



THE Clyde Drift-deposits extend to at least 230 feet below sea-level, 1 and to 

 1750 feet above it. 2 In a bore at Millichin, near Garscadden, 355 feet of 

 drift-beds were passed through, the bottom being 221 feet below the present 

 sea-level. These contained probably six Boulder-clays of varying shades of 

 colour. 3 In another bore at Drumry the bottom of the drift was 230 feet 

 below sea-level. 



It has been shown by Messrs. Croll and Bennie that a deep drift-filled 

 gutter extends between the Clyde and the Forth in the hollow at present 

 occupied by parts of the River Kelvin and the River Carron. As far as 

 borings give the information the highest part of that hollow cannot be far, 

 geographically, from the present watershed at Kilsyth, the bottom of the 

 trough there being 15 to 20 fathoms below the level of the canal The 



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hollow E. of that deepens even more at least 252 feet below sea-level than 

 that yet proved on the Clyde side. Several Boulder-clays have been passed 

 through in the bores (as on the Clyde end of the hollow), but in the shallow 

 portion near Kilsyth " only sand and gravel has been found." Shells of 

 mollusca and foraminifera have been occasionally recorded from these beds, but 

 no attempt was made to "work" them systematically for organic remains 

 when the borings were made. At a little below and above sea-level a series 

 of beds with Arctic shells, etc., is found, but as they are evidently of more 

 recent date than the drift-beds higher up country I shall take the latter as 

 first in order. 



THE DRIFT ABOVE SEA-LEVEL. 



The drift is only occasionally seen on the shore-level, as at Ardneil Bay, 

 where the surface is composed of a tough reddish Boulder-clay ; on the 

 Garnock Water and the Water of Irvine ; on several parts of the coast 

 between Gourock and Skelmorlie; and in some of the sea-lochs. This 

 paucity of drift on the sea-margin is owing to the immense time that the 

 waves must have acted both on it and the adjoining rocks during the Raised 

 Beach period, and also the recent one when it was cut off from that below 

 sea-level. The last Raised Beach epoch is represented in the Clyde by a 

 platform or terrace about 10 feet above high-tide mark, and that it was of 

 great duration is shown by the present line of cliffs on its landward side. 



1 J. Bennie, Trans. Geol. Soc. of Glasgow, vol. iii., part 1, 1868, p. 139. 

 2 The author, Ibid., vol. xi., supplement, 1898, p. 83. 

 3 J. Bennie, Ibid., vol. iii., part 1, 1868, p. 139. 



