448 A POPULAR EXPOSITION OF THE 
figure, for instance, are met with almost everywhere, producing undu- 
lating or rolling 
55 countries. Here 
it is evident that 
the strata were 
once continuous 
in the space be- 
tween a and 6b. 
Valleys thus resulting from the removal of strata, are termed “‘valleys 
of denudation.” Some of these valleys are many miles in breadth. 
Their excavation, consequently, could not have been caused by the 
streams which may now occupy their lower levels. Their formation 
is universally attributed to the denuding action of the sea during 
the gradual uprise of the land in former geological epochs. Fre- 
quently isolated patches of strata are left by denudation, or are cut 
off by wide distances from the rocks of which they originally formed 
part. These are termed ‘ outliers.” Thus in Western Canada, small 
isolated areas, occupied by bituminous shales of the Devonian series, 
occur in the townships of Enniskillen, Mosa, &c., and constitute out- 
liers or outlying portions of the Chemung and Portage group (see 
Part V.), as largely developed in the adjoining peninsula of Michigan. 
The matter carried off in some districts by denudation, must have 
been of enormous amount; and when it is considered that rost of 
the inequalities on the Earth’s surface—those at least not immediately 
connected with mountain chains—have arisen from this action, it will 
readily be perceived that materials for the formation of newer strata 
were abundantly provided by this means alone. 
(c) Tilting up and Fracturing of Strata.—Whilst some strata re- 
tain their original horizontality, others are more or less inclined, and 
some few occupy a vertical and even a recurved position. That strata 
were not originally inclined, at least to any extent, is proved by the 
known arrangement of sediments when diffused through water,—these 
(with the exceptional cases already pointed out) always depositing 
themselves in horizontal, or nearly horizontal, layers. The same fact 
