James Croll — Transport of Wastdale Crag Blocks. 17 



The fact that'in Westmoreland the direction of the ice-markings, 

 as a general rule, corresponds with the direction of the main valleys, 

 is no evidence whatever that the country was not at one period 

 covered with a continuous sheet of ice ; because, for long ages after 

 the period of continental ice, the valleys would be occupied by 

 glaciers, and these, of course, would necessarily leave the marks 

 of their presence behind. This is just what we have everywhere 

 in Scotland. It is on the summits of the hills and elevated ridges, 

 where no glacier could possibly reach, that we find the sure evidence 

 of continental ice. But that land-ice should have passed over the 

 tops of hills 1,000 or 2,000 feet in height is a thing hitherto re- 

 garded by geologists as so unlikely that few of them ever think of 

 searching in such places for ice-markings, or for transported stones. 

 Although little has been recorded on this point, I hardly think it 

 likely that there is in Scotland a hill under 2,000 feet wholly desti- 

 tute of evidence that ice has gone over it. If there were hills in 

 Scotland that should have escaped being overridden by ice, they were 

 surely the Pentland Hills ; but these, as was shown on a former 

 occasion,^ were completely buried under the mass of ice covering 

 the flat surrounding country. I have no doubt whatever that if the 

 summits of the pennine range were carefully examined, say under 

 the turf, evidence of ice-action, in the form of transported stones or 

 scratches on the rock, would be found. 



Nor is the fact that the Wastdale Boulders are not rounded and 

 ice-marked, nor found in the Boulder-clay, but lie on the surface, 

 any evidence that they were not transported by land -ice. For it 

 would not be the stones under the ice, but those falling on the upper 

 surface of the sheet, that would stand the best chance of being carried 

 over mountain ridges. But such blocks would not be crushed and 

 ice-worn ; and it is on the surface of the clay, and not imbedded in. 

 it, that we should expect to find them. 



It is quite possible that the dispersion of the Wastdale Boulders 

 took place at various periods. During the period of local glaciers 

 the blocks would be carried along the line of the valleys. 



All I wish to maintain is that the transport of the blocks across 

 the pennine chain is easily accounted for if we admit, what is very 

 probable, that the great ice covering of Scotland overlapped the 

 high grounds of the North of England. The phenomenon is the 

 same in both places, and why not attribute it to the same cause ? 



There is another curious circumstance connected with the drift of 

 England which seems to indicate the agency of an ice-covering. 



As far back as 1819, Dr. Buckland, in his Memoir on the Quartz 

 Eock of Lickey Hill,^ directed attention to the fact, that on the 

 Cotteswold Hills there are found pebbles of hard red Chalk which 

 must have come from the Wolds of Yorkshire and Lincolnshire. 

 He pointed out also that the slaty and porphyritic pebbles probably 

 came from Charnwood Forest, near Leicester. Mr. Hull, of the Greo- 

 logical Survey, considers that " almost all the Northern Drift of this 



1 Geol. Mag. for June, 1870. 



2 Trans. Geol. Soc, vol. y., p. 516 (First Series). 



VOL. Vm. — KO. LXXIX. 2 



