784 DYNAMICAL GEOLOGY. 



along for twenty miles, in which occur corals modern in aspect ; and that the existence 

 in Lake Titicaca, of eight species of a salt-water genus of Crustaceans, Allorchestes, 

 suggests the presence of the sea over this region, 12,500 feet in height, at no very dis- 

 tant period. On north circumpolar changes of level, see, further, H. H. Howorth, in 

 the Journal of the Royal Geographical Society, xliii., 240. 



The facts of geology show that the earth's surface has never yet 

 been at rest. They prove, 



First : The actuality of change of level through movements in the 

 earth's exterior. 



Secondly : The fact of unequal changes, in progress simultaneously, 

 in different parts of the same continent or continental region. 



Thirdly : The fact of vastly greater changes of level in geological 

 time after the commencement of the Tertiary than in the earlier pe- 

 riods of the Paleozoic and Mesozoic. 



Fourthly: The fact of similar simultaneous movements on opposite 

 sides of the Atlantic; as indicated by the parallelism between Europe 

 and America in the conditions and kinds of rocks in progress in some 

 periods and exemplified remarkably in the Subcarboniferous lime- 

 stones ; the coal-measures ; the Triassic strata ; the contrast between 

 the Jurassic and Triassic beds as to prevalence of fossils and in other 

 respects ; the Glacial phenomena ; the Champlain period of subsidence. 



No lessening of the amount of oceanic waters, whether by abstrac- 

 tion of part to make ice, or by any other method, can explain the 

 facts. Such causes, whose effects should exist along the borders of all 

 the continents alike, are often appealed to; but no statement of paral- 

 lel facts from the different continental borders has ever been presented 

 in order to sustain the opinion. The deepening of the ocean's bed may 

 produce the parallel movements of America and Europe just referred 

 to; but if so, the cause is, none the less, change of level in the earth's 

 crust — though change in the part beneath the ocean. 



No change in the position of the centre of gravity can produce the 

 effects mentioned ; for this would give an even curve to the surface of 

 the water far wide of that required by a difference in water level of 

 450 feet between the parallels of 45£° and 41 1° (the former that of 

 Montreal, the latter that of the southern coast of New England), with 

 only 25 feet for the latter. 



Inequalities in the contraction of the earth attending its original 

 cooling cannot account for the existence of mountains ; and appeals to 

 the earth's rotation during early periods, and to other astronomical 

 conditions, are equally unsatisfactory. For (1) slowly progressing sub- 

 sidences have taken place beneath the continents that much exceed in 

 extent of movement the elevations ; (2) subsidences and elevations 

 have taken place alternately ; and (3) the great mountains of the globe 



