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POPULAR SCIENCE REVIEW. 
the rocks of the Midland Counties. In the vale of Moreton 
Professor Hull found erratic boulders from two to three feet 
in diameter, and the granite boulders of Shap Fell are found 
transported to great distances. The evidences of glaciation 
in West Somerset exist in the form of “rounded rocky knolls,” 
and beds of gravel and clay, regarded as “boulder-clay,”* 
similar to that which is found under the recent glaciers of 
Switzerland. Near the Dodman, in Cornwall, Mr. C. W. 
Peach found, at an elevation of 60 feet above the sea level, 
the rock surface well “ striated and ice polished.” Chalk flints 
are found in abundance upon Haldon, near Exeter ; they are 
scattered over the wilds of Dartmoor, and not only are they to 
be found around the Land’s End, but they are spread, — sparsely 
it is true, — over the Isles of Scilly, and they have been dis- 
covered imbedded in the mineral lodes of the mines west of 
Penzance. 
The striae and ice- groovings found on the rocks of these 
islands — to which we have directed attention — perfectly re- 
semble the flutings and striae produced in the Alps by the 
present movements of glaciers, that neither M. Agassiz, or those 
geologists who have followed him in this path of observation, 
could detect a difference. The transportation of rock masses 
to considerable distances could only have been effected by the 
movements of fields of land-ice, by the floating power of ice- 
bergs. The conditions under which the “ boulder-clays ” are 
found, and the marked peculiarities of the “ glacial drift,” 
sufficiently show that they were produced in this country in 
Tertiary times, as they are, in our own times, in Switzerland. 
The conclusion to be drawn from these facts is that an ice- 
covering must at some period have been spread over the whole, 
or very nearly the whole, of the British Isles. This ice-covering 
appears to have extended indeed over the whole of north- 
western Europe, and to have moved by the way of the North 
Sea over Scotland, and gradually over Wales and England. 
A word on this movement is necessary. An ordinary glacier 
descends in virtue of the slope of its bed, and it is thin at 
its commencement and thickens as it descends into the lower 
valleys, where the slope is less and the resistance to motion 
greater. The condition of ice formed on level or nearly level 
land — continential-ice — is different; the slope of the ground ex- 
ercises little or no influence on the motion of such ice. The ice 
* The glacial drift of Caithness is particularly interesting as an example 
of a boulder clay , which, in its mode of accumulation, and ice-scratched debris, 
very much resembles that unstratified stony mud which occurs under 
glaciers — the moraine profonde , as some call it. — Jamieson, u Quart. Jo urn. 
Geol. Soc.” vol. xxii. p. 261. 
