OF THE LEVEL OF THE SEA. 55 



must be inferred from the confused manner in which the 

 different parts of the till are arranged. Submarine currents 

 might indeed have moved the largest boulders, but they 

 must have been deposited somewhat in the order of size and 

 gravity ; the sand, clay, and smaller fragments being swept 

 forward till the diminished velocity of the current was un- 

 equal 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 dis- 

 turbed the alluvial covering both above and below the sur- 

 face of the sea. 



All observers concur in supposing that the cause which 

 produced the diluvial covering of the great-coal field of 

 Scotland, must have had its origin to the westward, modi- 

 fied, however, by the form of the ground. Near Glasgow, 

 it is quite evident that its action must have been from the 

 north-west. In levelling 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 re- 

 lative proportions of the different rocks, which I found to 

 be as follows : — 



White sandstone and shale, 60 per cent. 



Trap, ... 30 



Clay -slate and grey wacke, 10 

 Granite, - - - 1 ... 



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 which they contained ; 

 the slate and greywacke from hills in Dumbarton and 



