454 POPULAR EXPOSITION OF THE GEOLOGY OF CANADA. 
(2) In Canada proper, the following series alone occur : 
Modern formations. 
Drift deposits. 
Carboniferous series (in part only, in Gaspé.) 
Devonian series. 
Silurian series. 
Huronian series. 
Laurentian series. 
These comprise, lithologically, various sedimentary and metamor- 
phic strata, with, in some cases, accompanying eruptive rocks, as 
described fully in Parr V. 
(3) One or more of several consecutive formations (as shewn in 
Note 2) are often “wanting” or absent at a given spot. The Car- 
bonifeorus rocks may thus, in certain districts, be found resting on the 
Silurian, without the imtervention of the Devonian series. But the 
relative positions of these groups are never reversed. The Devonian 
beds are never found under the Silurian, for example, nor the Creta- 
ceous under the Jurassic. The absence of particular strata, at a 
given locality, is accounted’ for by the elevation of the spot above the 
sea-level during the period to whieh the strata in question belong; 
by denudation, or by the district having been situated beyond the 
area of deposition to which the sediments extended. (See some of — 
the preceding observations under “ Formation of Sedimentary Rocks,” 
“‘Denudation,” &c.) 
(4) A formation of a given age may be represented in one place 
by a limestone; in another, by a sandstone ; in a third, by argilla- 
ceous shales, and so on. ‘This will be easily understood, if we reflect 
that at the present day these different kinds of rock are being formed 
simultaneously at different places. Many of our preceding observa- 
tions have amply illustrated this, but the fact may be rendered still 
clearer by the accompanying diagram. In this sketch, the dark out- 
line is intended to represent a somewhat extended line of coast, with 
a river debouching into a deep bay. In the latter, the argillaceous or 
muddy sediments (m), brought down by the river, may be deposited. 
At G, we may suppose a granitic headland. The arenaceous or 
siliceous sediments (s) derived from the disintegration of this, will be 
arranged along the shore beyond it, by the set of the current. 
Finally, at L, we may suppose the occurrence of exposed cliffs of 
