Crosby.] 452 [November 7, 



THEORIES OF THE* ORIGIN OF CONTINENTS AND OCEAN-BASINS. 



Taking a general view, the theories or explanations of the ori- 

 gin of continents and ocean-basins may be regarded as two in 

 number. A brief statement of each of these will be first in order ; 

 and after that we will consider more in detail the arguments that 

 oppose or support them. 



1. We have, first, what may be called the old theory, the one 

 taught by Lyell and all the older geologists and still very gener- 

 ally accepted. This is the theory held by the present writer ; 

 and hence the following statement of it on account of the per- 

 sonal coloring may not, as a whole, meet the views of those who 

 would still indorse its main features : The mobile stratum be- 

 tween the solid nucleus and the solid exterior lies at the founda- 

 tion of this theory ; for the continents and ocean-basins are here 

 regarded as broad upward and downward bendings of the crust. 

 These great crust-flexures are produced and sustained by the 

 tangential thrust arising from the contraction of the earth's inte- 

 rior. The final result of the increasing horizontal strain in the 

 crust is that the crust is mashed up and a mountain-range formed. 

 No crushing can take place, however, until the strain reaches a 

 certain high maximum ; for otherwise it would go on all the time, 

 and we would recognize no distinct mountain-building epochs in 

 the earth's history. But I hold that, until the crust can obtain 

 final and permanent relief by crushing, it will accommodate itself 

 to the shrinking nucleus by undergoing a grand distortion or 

 warping, which will be slight in the vertical direction when the 

 strain is small, but as the strain accumulates during the lapse of 

 ao-es the deviation from the normal spheroidal form will tend to 

 become greater — the continents higher and the oceans deeper — , 

 though this may not actually occur in every case because denud- 

 ation is constantly degrading the land and filling up the seas. It 



thick; and on this basis we can reconcile the conclusions of the geologists and physicists. 

 It is doubtful, however, if physicists will accept Major Powell's novel argument from the 

 "flow of solids ;" namely, "that pressure itself would reduce the interior of the earth 

 to a fluid condition." Dr. M. E. Wadsworth (American Naturalist, xvin, 587) points 

 out the self evident fact that Thomson and Darwin necessarily assumed as the basis of 

 their reasoning conditions different from those of the actual earth. But he has not 

 shown that the difference is of such nature as to necessarily or even probably invali- 

 date their conclusions. 



