in the Geological History of North America. 



339 



tures of the land ; that the same cause which originated the one, 

 impressed peculiarities on the other ; that the two had a parallel 

 history through past time — the oceanic depressions tending down- 

 ward, the continents upward ; in other words, that they have 

 both been in progress with mutual reaction from the beginning 

 of the earth's refrigeration. The continents'^ have always been 

 the more elevated land of the crust, and the oceanic basins always 

 basins, or the more depressed land. 



We thence learn that the profounder features of the earth were 

 marked out in the earliest beginnings of geological history, and 

 that the whole subsequent progress has been a working on this 

 basis. Other and more direct evidence of this fact I alluded to 

 in my address before this Association last year — evidence derived 

 from the extent and nature of the Potsdam sandstone, the earli- 

 est of the Silurian strata, showing that this primal rock was laid 

 down over a large part of North America by a sea which just 

 bathed its surface — thus proving that the continent was already 

 made, and indicating in part its water level. 



The relation between the extent of the oceans and the border 

 features of the continents, which has been pointed out, is not 

 simply a relation of fact, but of effect and dynamics, pointing 

 to a unity of cause. The one cause is assuredly not in the waters 

 of the oceans, for these are inert : they cannot bake rocks, light 

 up volcanoes, fold the heavy strata, and make mountains. The 

 cause is no paroxysmal force, exhausted in a temporary freak of 

 nature. It is some profound, systematic, untiring force, which 

 in its slow movement, has counted centuries as if seconds. The 

 Appalachian range is one mark of its power ; but not the result 

 of a fitful heave : on the contrary, a work of time, and time so 

 long, that the resisting strata could bend in many plications with- 

 out being reduced to chaos ; so long, that New England and re- 

 gions south, which entered the period of catastrophe as a territory 

 of sedimentary beds, came forth at last a region of granite, gneiss 

 and crystalline schists. Most of the mountains of the globe, for 

 the reasons stated, we must regard as other effects of this funda- 

 mental cause ; and it is therefore no matter of surprise that they 

 should have in general a common system of structure. 



A unity of cause there must be for the great phenomena of 

 geology. Such is nature in all her departments. Details are the 

 means by which we penetrate to the deep-seated cause ; and when 

 that cause is once reached and fully apprehended, the details have 

 new interest from the harmonious relations thus developed, — as 

 the leaves and twigs of a tree derive their grandeur and the most 

 of their beauty from the rising trunk and spreading branches to 

 which they are subordinate, and with which they are in perfect 

 harmony. 



What then is the principle of development through which 

 these grand results in the earth's structure and features have been 



