WORLD-MAKING 33 



of the problem is understood by many geologists, its solution 

 in particular cases is still a source of apparently endless 

 debate. 



The causes and mode of operation of the great movements 

 of the earth's crust which have produced mountains, plains 

 and table-lands, are still involved in some mystery. One 

 patent cause is the unequal settling of the crust towards the 

 centre ; but it is not so generally understood as it should be, 

 that the greater settlement of the ocean-bed has necessitated 

 its pressure against the sides of the continents in the same 

 manner that a huge ice-floe crushes a ship or a pier. The 

 geological map of North America shows this at a glance, and 

 impresses us with the fact that large portions of the earth's 

 crust have not only been folded but bodily pushed back for 

 great distances. On looking at the extreme north, we see that 

 the great Laurentian mass of central Newfoundland has acted 

 as a projecting pier to the space immediately west of it, and 

 has caused the gulf of St. Lawrence to remain an undisturbed 

 area since Palaeozoic times. Immediately to the south of this, 

 Nova Scotia and New Brunswick are folded back. Still farther 

 south, as Guyot has shown, the old sediments have been 

 crushed in sharp folds against the Adirondack mass, which has 

 sheltered the table-land of the Catskills and of the great lakes. 

 South of this again the rocks of Pennsylvania and Maryland 

 have been driven back in a great curve to the west. Move- 

 ments of this kind on the Pacific coast of America have been 

 still more stupendous, as well as more recent. Dr. G. M. 

 Dawson ^ thus refers to the crushing action of the Pacific bed 

 on the rocks of British Columbia, and this especially at two 

 periods, the close of the Triassic and the close of the Cretace- 

 ous : " The successive foldings and crushings which the Cor- 

 dillera region has suffered have resulted in an actual change 

 of position of the rocks now composing its western margin. 

 ^ Trans. Royal Society of Canada, 1890. 



