746 DYNAMICAL GEOLOGY. 



force, characterize the borders of the greatest oceans, shows that the 

 lateral pressure from the direction of the oceans was approximately 

 proportional to the extent of the oceanic basins. 



3. Comprehensiveness of the action of Lateral Pressure. — The uni- 

 versality of the great movements resulting from the earth's cooling 

 and contraction is manifested, not only in the relations existing be- 

 tween the continental features and the positions of the oceanic basins, 

 but also in the fact that cotemporaneous, parallel movements have taken 

 place in the continents on the opposite sides of the same ocean, and in 

 some cases in all continents together. Thus, the Trenton jjeriod in 

 the Lower Silurian was a period of extensive submergence, both in 

 North America and in Europe ; so also was the Niagara period, in the 

 Upper Silurian ; and the Subcarboniferous period. Again, the period 

 of the Coal-measures was one of general emergence, over both conti- 

 nents, but of small emergence, with very long intervals without, or 

 with scarcely any, change of level, sufficient for the making of great 

 beds of vegetable debris. The Triassic was an era of salt-marsh and 

 estuary formations, containing few fossils, both in Europe and Amer- 

 ica, facts showing again a like condition on both sides of the ocean. 

 On the contrary, the Jurassic was, in America and Europe, a period 

 of more submergence than the Triassic. The great era of mountain- 

 making, which commenced in the early Tertiary, and continued to its 

 end, was a mountain-making era for all continents alike ; in Asia and 

 South America, as well as Europe and North America, mountain 

 ranges were raised over 10,000 feet. 



Again, the destruction of species following the close of the Per- 

 mian was as complete in America as in Europe ; and that closing the 

 Cretaceous was scarcely less universal. The upward, downward, and 

 again upward movements of the crust in the Quaternary age, corre- 

 sponding to the Glacial, Champlain, and Recent periods, affected the 

 higher latitudes of the northern hemisphere, on all its sides ; and it is 

 probable that these movements of the northern hemisphere were 

 attended by parallel movements in the southern. 



Again, along the Atlantic Border of North America, the mountain 

 ranges made at different times have on any part the same course (p. 

 393); and so also, along the Pacific Border: indicating that the all- 

 pervading force was in. each place at its old work, through all the suc- 

 cessive ages, with but small modifications from the changed conditions. 



The force has thus acted as if one in origin and nature, and mani- 

 fested at all times the fact that one" single system of evolution was in 

 progress. 



3. Influence of the Cleavage Structure of the Globe on the developments 

 in progress. — While the relative positions of the continental plateaus 



