166 THE RECENT. 



heavier fragments. In Europe, Asia, and North America, 

 down to the 44th or 42d parallel of latitude, and up to the 

 altitude of 2000 feet, these appearances present themselves, 

 and are inexplicable, unless on the ground of the gradual 

 submergence of the northern hemisphere to that extent, 

 and its subjection to a boreal climate which engendered 

 glaciers on its hills, and drifted, during a brief summer, 

 icebergs laden with rocky debris over its waters. The 

 glaciers smoothing, rounding, and grooving the rocks of the 

 higher grounds the icebergs grinding their way through 

 firth and strait, dropping their burden of mud, sand, and 

 gravel on the sea-bed, or stranding themselves on its shores 

 complete the necessary arrangements for the production 

 of the geological phenomena of the period. For ages the 

 pliocene lands must have slowly subsided, each step gra- 

 dually narrowing the boundaries of vegetable and animal 

 life, and driving the surviving species, under the rigours of 

 a deteriorating climate, to higher and higher regions. Eace 

 after race would succumb : first the more limited and local, 

 next the more cosmopolitan, and ultimately few of the old 

 flora or fauna would survive, except the more elastic in 

 constitution, and those that had, step by step, retreated into 

 more southern latitudes. 



How long these conditions continued we have no means 

 of determining in centuries, but, judging from the amount 

 of denudation, the extent and nature of the heterogeneous 

 deposits, as well as from the slow rate of elevation and sub- 

 mergence now going on in known regions, vast periods 

 must have elapsed during the manifestation of this glacial 

 epoch. At length the downward tendency of these north- 

 ern latitudes comes to a close ; submergence stops and 

 elevation begins. Slowly, and for long under a rigorous 

 climate, the lands of Europe, Asia, and North America 

 emerge from the waters. Glaciers still envelop the higher 



