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POPULAR SCIENCE REVIEW. 
and two Greenlanders.* They penetrated thirty miles into the 
interior in four days, attaining an altitude of 2,200 feet above 
the level of the sea. 
Ho moraine-matter was observed on the surface of the ice ; 
but everywhere, under the influence of the sun’s rays, this im- 
mense ice-field was in motion internally, and large rivers and 
lakes on its surface descended through the ice in roaring tor- 
rents, by 66 swallow-holes ” 2,000 feet deep, to join the streams 
which flowed beneath. 
The ice-sheet which some geologists believe to have been 
once co-extensive with our island, covering it from its sea-level to 
the highest peak of its loftiest mountains in Wales or Scotland, 
was, it is assumed, only a repetition of the present state of 
Greenland, or, on a larger scale, of what one may see taking 
place to-day on the Alps and the Himalayas and other moun- 
tain ranges, whose heads are covered by perennial snows. For 
the process of reduction of temperature takes place in a cor- 
responding ratio, whether we sail to the Xorth Pole with the 
Alert and Discovery, or with Professor Tyndall scale the heights 
of the Matterhorn or Monte Eosa. 
If, then, temperature decreases with altitude above the sea- 
level, an elevation of our island would produce the same effect 
upon it as if we could transport it bodily to the latitude of 
Greenland ! 
It is well to keep these facts clearly before the mind, because, 
among the numerous explanations offered by our leading geolo- 
gists, this question of the relative elevation above the sea-level 
has not had that prominence given to it in the discussion which 
it deserves. The results of altitude, have in fact been confounded 
with those of latitude. 
The stones that occur in the boulder-clay spread over so 
many counties in England differ widely in character ; and, 
from a study of these, it is possible to determine the direction 
in which the ice-sheet moved, and the centres of dispersion 
whence the boulders were derived. 
Wherever the surface of the rock is of sufficient hardness it 
is everywhere polished, rounded, and striated in a precisely 
similar manner to what is seen to be taking place in valleys oc- 
cupied by glaciers at the present day ; whilst the boulder-clay is 
the finely comminuted particles worn down to powder, like the 
grains of wheat into flour, by the glacial millstone, and poured 
out in a turbid stream, or pushed along as a great rampart of 
stones and rubbish forming the terminal moraine, as we see it 
at the foot of the Mer de Glace, above Chamounix, or, at times, 
* The Greenlanders turned hack after two days, hut Xordenskiold and 
his companion pushed cn two days’ journey further. 
