660 MR DAVID MILNE HOME ON THE BOULDER-CLAY OF EUROPE. 



If the boulder-clay was produced by glaciers, its transport would be coinci- 

 dent with the direction in which the glaciers moved — that is, in directions parallel 

 with the valleys from which they emerged. We should expect, therefore, to find 

 that the boulder-clay, and the blocks embedded in it, indicated a movement and 

 transport from every conceivable point. The boulder-clay and boulders found on 

 the west coast of Scotland should indicate a movement from the eastward ; on 

 the north coast, from the southward ; and on the east coast, from the west- 

 ward. 



But is this the true state of the case, as shown by most recent observation ? 

 The phenomena of the boulder- clay show in all parts, not of Scotland only, but 

 of Ireland, England, and even of the adjoining districts of North- Western Europe, 

 a general movement from the north-westward. That exceptions to the rule exist 

 I admit, and an explanation of these I shall afterwards offer ; but I affirm that 

 there is a general and prevailing direction over the wide area just mentioned, 

 and that direction is from W.N.W. or N.N.W. 



Before, however, giving proofs of this position, let us see what are the signs 

 of transport on which geologists are agreed. 



(1.) Mr Geikie has pointed out a relation between the colour of the boulder- 

 clay and the rocks of the districts adjoining the deposit — as indicating transport. 

 Thus he says — " The main mass of the boulder-clay, in the basin of the Forth 

 for instance, consists of the comminuted debris of the carboniferous and other 

 rocks which form the framework of that district. We can also gather that this 

 loose fragmentary material has moved (there ?) from west to east. In the upper 

 part of the basin of the Firth of Forth, the coal-fields are covered with red boulder- 

 clay, abounding in fragments of the rocks that lie towards the N.W., and deriving 

 its prevalent tint from the waste of the Old Red Sandstone which stretches up to 

 the foot of the Highland mountains."* 



The late Hugh Miller had previously pointed out how the pale oolitic rocks of 

 Brora and Golspie are covered by a yellow boulder-clay, and the flagstones of 

 Caithness are covered by a boulder-clay of a grey leaden colour. So also Mr 

 Cumming showed how, in the Black Isle, the boulder-clay has the colour of the 

 red rocks there ; whilst to the westward, the colour changes to a colour in corres- 

 pondence with that of the slaty rocks. The same author points out how, in the 

 Isle of Man, the colour of the boulder-clay is blue near the limestone rocks, and 

 red near the Old Red Sandstone rocks ; and how in each case these rocks are in 

 the same direction from the boulder-clay, as if a current had swept over the rocks 

 to provide materials for the clay.f 



Mr Nicol has pointed out the same relationship in Cantyre.J 



* Glacial Drift, p. 43. 



f Lond. Geolog. Journal for 1850, vol. vi. — Isle of Man, pp. 115, 247. 



J Lond. Geolog. Journal for 1852, vol. viii. p. 417. 



