GENERAL OBSERVATIONS. 587 



latitude oscillations, being most prominent over the colder latitudes of 

 the globe, the cold-temperate and Arctic ; (2) they were movements 

 of the broad areas of the continents ; (3) they brought no mountain 

 ranges into existence. 



According to the view presented in the preceding pages, there was 



(1) an upward oscillation over the higher latitudes, in the Glacial period ; 



(2) a downward, introducing the Champlain period, and then (3) an 

 upward of moderate extent, introducing the Recent period. The 

 Champlain subsidence submerged the region about Montreal and the 

 Ottawa, so that marine shell deposits were there formed, — an event 

 which had not previously occurred since the Lower Helderberg period 

 in the Silurian age (p. 215). It submerged a large part of Britain to 

 500-1,400 feet below its present level, and much also of Europe, 

 thereby giving an opportunity for the deposition of the thick river- 

 border formations that prevail so extensively. But the elevation 

 closing the Champlain period appears to have gone on, in Europe, until 

 the continent stood above its present level, and, in connection, a sec- 

 ond Glacial epoch intervened, separating the Champlain and Recent 

 periods ; and it may be that North America also was raised to a higher 

 level than now, though with less marked glacial effects (p. 561). Thus 

 the course of the movements was diverse from that of earlier time, and 

 so also their results. 



During the Quaternary, some of the most prominent dynamical agen- 

 cies on the globe were intensified vastly beyond their former power : — 



(1.) Owing to the completion of the great mountain-chains and the 

 expansion of the continents, the heights for condensing moisture, and 

 the extent of slope for its accumulation into rivers, had augmented 

 many fold. Moreover, through the union of lands before isolated by 

 seas, into continental areas, the rivers draining immense regions were 

 for the first time united into common trunks. The Quaternary was 

 therefore eminently the era of the first grand display of completed 

 river-systems, — of the first Amazon, Mississippi, Ganges, Indus, Nile, 

 etc. 



(2.) The elevation of the mountains to snowy altitudes made gla- 

 ciers — powerful dynamical agents. 



(3.) The increase of cold, and the existence finally of true frigid 

 zones, due partly, at least, to an increase of polar lands after the close 

 of the Cretaceous period and through the Tertiary, gave a vast extent 

 to glaciers, rendering them possible in regions where otherwise they 

 could not have existed. 



(4.) The cause last mentioned also gave origin to icebergs. 



Great rivers, glaciers, and icebergs were especially characteristic of 

 the Quaternary ; and the ice accomplished what was impossible for the 



