238 
POPULAR SCIENCE REVIEW. 
•eye of the geologist can ever constitute a science of geology 
any more than a description and classification of the effects of 
heat could constitute a science of heat. . . . The principles of 
lieat are the laws of heat, the principles of electricity are the laws 
of electricity, and these laws are nothing more nor less than 
the ways according to which these agents produce their effects. 
The principles of geology are therefore the laws of geology ; 
hut the laws of geology must be simply the laws of the geo- 
logical agents ; or, in other words, the methods by which they 
produce their effects. . . . The facts of geology are as essential 
to the establishment of the principles as the facts of heat, light, 
and electricity, are essential to the establishment of the prin- 
-eiples of those sciences.” 
Remembering this, let us advance to a careful examination 
of the phenomena which have been observed by the trained 
geologist, and which may be noted by everyone, leading the 
thinking mind to the conclusion that our globe has undergone 
changes of climate of the most extraordinary character, con- 
vincing us that at one time not only an arctic climate prevailed 
in our island, but that the greater part of the now temperate 
regions was buried under ice. 
Passing through many of the valleys of North Wales, and 
especially through that of Llanberis, we cannot but observe 
that the rocks are round and mammilated, that their smoothed 
surfaces are often grooved, the striations in this particular in- 
stance running north-west, in the direction of the valley, and of 
the length of the lake. Proceeding up the pass of Llanberis, 
erratic boulders, mingled with smaller moraine matter, are seen 
lying on the road side and up among the rocks, which are 
clearly distinguished from the more modern blocks, and the 
talus that lie below the weathered cliffs. On both sides of the 
valley the rocks strewn into blocks frequently present the 
moutonnee (rounded) form. The author already quoted* thus 
describes one section of this wild and instructive scene : — “ Near 
Pont-y-gromlech bosses of felspathic porphyry rise like little 
hills in the middle of the valley, something like miniatures of 
that behind the Grrimsel. Though their sides have been scarred 
by winters’ frost and their summits roughened by the weather, 
they still retain the mammillated form impressed on them of old 
by the grinding ice ; and while the tourist, who sees something in 
scenery beyond mere external form, is often puzzled to account 
for the numerous blocks that, perched on precarious points, 
seem as if they ought to have taken a final bound into the 
lowest valley, the well-pleased eye of the geologist versed in 
ice at once detects that they were let gently down where they 
* Ramsay, u The Old Glaciers of Switzerland and North Wales.” 
