86 
ISLAND LIFE. 
[part I. 
It is there that nature has always strewn the dust of continents 
to be.” 
The Movements of Continents . — As we find these stratified 
rocks of different periods spread over almost the whole surface 
of existing continents where not occupied by igneous or meta- 
morpbic rocks, it follows that at one period or another each 
part of the continent has been under the sea, but at the same 
time not far from the shore. Geologists now recognise two 
kinds of movements by which the deposits so formed have been 
elevated into dry land — in the one case the strata remain 
almost level and undisturbed, in the other they are contorted 
and crumpled, often to an enormous extent. The former often 
prevails in plains and plateaus, while the latter is almost always 
found in the great mountain ranges. We are thus led to picture 
the land of the globe as a flexible area in a state of slow but 
incessant change ; the changes consisting of low undulations 
which creep over the surface so as to elevate and depress limited 
portions in succession without perceptibly affecting their nearly 
horizontal position, and also of intense lateral compression, 
supposed to be produced by partial subsidence along certain 
lines of weakness in the earth’s crust, the effect of which is to 
crumple the strata and force up certain areas in great contorted 
masses, which, when carved out by subaerial denudation into 
peaks and valleys, constitute our great mountain systems . 1 In 
this way every part of a continent may again and again have 
sunk beneath the sea, and yet as a whole may never have 
ceased to exist as a continent or a vast continental archipelago. 
1 Professor Dana points out that the regions which, after long under- 
going subsidence, and accumulating vast piles of sedimentary deposits, 
have been elevated into mountain ranges, have thereby become stiff and 
unyielding, and that the next depression and subsequent upheaval will be 
situated on one or the other sides of it ; and he shows that, in North 
America, this is the case with all the mountains of the successive geological 
formations. Thus, depressions and elevations of extreme slowness but 
often of vast amount, have occurred successively in restricted adjacent 
areas ; and the effect has been to bring each portion in succession beneath 
the ocean but always bordered on one or both sides by the remainder of 
the continent, from the denudation of which the deposits are formed which, 
on the subsequent upheaval, become mountain ranges. (Manual of Geology , 
2nd Ed., p. 751.) 
