88 ISLAND LIFE 



from the cUhris of which they were origmally foi-med. 

 Again quoting Sir Archibald Geikie : — " The materials car- 

 ried down to the sea would arrange themselves then as they 

 do still, the coarser portions nearest the shore, the finer silt 

 and mud furthest from it. From the earliest geological 

 times the great area of deposit has been, as it still is, the 

 marginal belt of sea-floor skirting the land. 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 igne- 

 ous or metamorphic 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 perceiD- 

 tibly affecting their nearly horizontal position ; and also of 

 intense lateral compression, suj^posed 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.^ In this 



^ Professor Dana was, I believe, the first to point out that the regions 

 which, after long undergoing subsidence and accumulating vast piles of 

 sedimentary deposit have been elevated into mountain ranges, 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 has shown 

 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 occiirred successively in 



