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upon which these modem views are based, and, on the 
other, the objections to their wide application; and then to 
ascertain to what extent they may be received or rejected, 
following as far as we can the sure and solid path of deduction 
from the observed phenomena of nature, and endeavouring to 
shun the shadowy regions of fancy. 
If from our present stand-point we glance back at the days 
in which modern geology was in its infancy, we cannot fail to 
observe that we have, on the whole, made substantial progress 
in our views of the agencies by which the earth's surface has 
been moulded into form and feature. In those early days the 
notion prevailed that mountains and ridges were due to up- 
heaval, and that from an “axis of elevation" the strata 
invariably dipped in each direction towards the plains. Sub- 
sequent investigation, however, went to show that in many 
cases — even among the higher ranges, such as the Alps — the 
strata sometimes dip inwards towards the higher elevations, 
and consequently that the elevatory theory was by no means a 
universal, if indeed a general rule. According to the modern 
view — while admitting to a certain extent the influence of 
elevation — we regard the majority of hills and mountain chains 
as due to “ denudation," — a word which signifies, in this 
instance, the removal of masses of materials once overlying, 
or contiguous to, the more prominent elevations. The process 
may be illustrated by observing how, from the flat surface of 
a slab, a stone-mason will produce a figure in relief by chipping 
away the surrounding material. With regard to volcanic cones, 
that view may be said to be exploded, according to which 
they were supposed to have been blown up into “ craters of 
elevation," as it is now found that the sides of the cone, instead 
of being composed of the rocks which form its basis, consist 
of the erupted matter of the volcanoes themselves, which are in 
fact cones of deposition. 
On the other hand, deep valleys and narrow chasms amongst 
mountains were generally regarded as the result of earthquake 
action, rending the rocks in twain ; and such views are still 
to be found glowingly enlarged upon by amateur “ geologists" 
in local “guides but it is now considered exceedingly doubt- 
ful if the world contains, even in volcanic regions, a single 
instance of a chasm so formed, as it would have been filled up 
from below with molten matter — as a trap dyke — or from above 
with detritus. The chasms in mountains may therefore be in 
all cases referred to the action of water — to denudation. 
In a word, denudation by water, or in its crystalline form, 
by ice, has become, in the modern period of geological science, 
the recognised process by which the features of the laud were 
sculptured ; and to none is our science more indebted for this 
