Mr Smith on the Changes of the Level of the Sea. 383 



the largest boulders, but they must have been deposited some- 

 what in the order of size and gravity; the sand, clay, and 

 smaller fragments being swept forward till the diminished velo- 

 city of the current was unequal to bear them farther, and banks 

 of gravel, sand, and clay, would be formed. No inference can 

 therefore be drawn from it as to the former level of the land, as 

 rushes of water capable of producing such effects must have 

 disturbed the alluvial covering both above and below the sur- 

 face of the sea. 



All observers concur in supposing that the cause which pro- 

 duced the diluvial covering of the great-coal field of Scotland, 

 must have had its origin to the westward, modified, however, 

 by the form of the ground. Near Glasgow, it is quite evident 

 that its action must have been from the north-west. In level- 

 ling a mass of it, the workman laid into a heap all the boulders 

 which were too large to be lifted by the spade : this afforded an 

 opportunity to estimate the relative proportions of the differ- 

 ent rocks, which I found to be as follows : — 



101 



The sandstone was evidently derived from the subjacent coal- 

 formation, the trap boulders from the Kilpatrick hills, which 

 are about ten miles to the north-west, their identity being 

 proved by the zeolitic minerals whicli they contained ; the slate 

 and greywacke from hills in Dumbarton and Argyleshires, 

 about double that distance ; the granite blocks must have been 

 transported from still greater distances. Beyond the Kilpatrick 

 Hills the trap and white sandstone boulders disappear, and are 

 replaced by greywacke, clay- slate, and red sandstone, whilst 

 those of granite and mica-slate become numerous. Near 

 Helensburgh, twenty-three miles to the north-west of Glasgow, 

 the granite strongly resembles that of Ardnamurchan. At 

 Roseneath, I have seen rolled fragments of a compact reddish 

 granite so much resembling that of Inverary, as to leave little 

 doubt of its identity. In all of these cases, the bearing of the 



