MACRIE — ROCKS AND THEIR TEACHINGS. 
07 
near. "We perceive at once they arc the d&hris of ancient cliffs, and 
our thoughts turn to the rough waves tliundering at their base, 
and foaming back from their incessant toil, repulsed by the crags and 
rocks, for weeks and months, only to prevail over and hurl down the 
stony masses in the end ; then, rolling and labouring the broken frag- 
ments aloug the shore, day and night, with the same monotonous 
cadence as soothes us now on the margins of the great waters, 
to fashion them into smooth and polished stones. Twenty feet 
of modern pebbles, a quarter of a mile broad, form a gi'eat beach. 
The great beach of the old red sandstone was probably two thousand 
feet thick. 
Perhaps, however, those wonderful accumulations of the Devonian 
period ought to be compared with the time and water-worn, 
semi-angular, and partially-rounded talus of the ]N"orth American 
mountains, which is strewn on the borders of the great lakes ; the 
boulders of such origin being usually larger and less smooth than the 
pebbles of the sea-shore, which are subject to more rapid and far more 
powerful attrition. The Permian conglomerates may also have 
proceeded from a like source ; and the intermediate coal-mea- 
sures, in their partly terrestrial and partly fresh-water and aestuarine 
characters and conditions, seem in no way discouraging to the 
comparison. 
We see, moreover, in the microscopic structure of many of those 
finer siliceous rocks, which are composed of a segregation of the solid 
cases of infusoria, and of limestones compounded of nearly equally minute 
entromostraca and foraminifera, the slowly-formed life-elaborated pro- 
duce of the tranquil lake, or of the profound abysses of the deep. 
Our ponds and inland seas give us the key to the one, the soundings 
for the great Atlantic telegraph that to the other. The silent language 
of the past, in which these facts are written, appears at first strange 
and unintelligible, as the tongue of our Saxon forefathers does to us 
now. But as the languages of the ancient peoples are interpreted by 
our own, and by those of contemporary nations, so the events and 
changes of the past conditions of our planet can only be understood by 
comparison with the phenomena going on around us. 
It is commonly stated that we are acquainted with something like a 
thickness of ten miles of the earth's crust — and what is that to the 
eight thousand miles diameter ? But we do not know absolutely so 
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