466 J. LeConte—Formation of the 
of marginal sea bottoms completely explains the well-known 
law of continental form, viz., that continents consist of interior 
basins with coast chain rims. In fact, the theory necessitates 
this as a general form of continents, but at the same time pre- 
pares us for exceptions in cases of mountains formed from 
mediterranean sediments. The view is best illustrated from the 
American continent, because of the regular manner in which 
lems seem to be reduced to their simplest terms, and therefore 
are most easily studied and understood in America. 
Prof. Dana, in a paper on “the plan of development of the 
American continent,”* brings out some grand views on the 
relation of the heights of coast chains and their position, to the 
size and depth of the uceans which they overlook. From these 
formal laws, and proceeding on the hypothesis of a fluid in- 
terior, he concludes that sinking sea bottoms, determined by 
interior contraction, is the force by which continents are 
elevated. According to him, the sinking sea bottoms, together 
with the lateral thrust produced by interior contraction, push 
up the continents, at the same time crumpling up their margins 
into mountain chains. Such a process might certainly account 
for coast chains, for their position at right angles to the 
greatest expanse of ocean, ind: for their heights and crumplings 
being in proportion to the size and depth of the contiguous 
oceans; but the mechanics of the process is, it seems to me, 
untenable. For observe: this subsidence cannot be gravitative 
subsidence; for this could not raise continents. It is evidently 
a concave bending of the sub-oceanic earth-crust pressing on the 
liquid interior, and through it pushing up the continental crust. 
Now I have already shown that no stiffness of crust—not even 
if the crust were several hundred miles thick—could stam 
such strain over such immense areas. While I admire, there 
fore, the formal laws of Prof. Dana, I cannot accept his phy sical 
explanation. ‘ 
c.) Parallel ranges.—Whitney, in his essay on Mountain 
Building, already referred to, has drawn attention to the a 
that the celebrated law of Elie de Beaumont, that paralle . 
ranges of mountains are of the same age, so far from being ue 
is nearly the opposite of the truth. Parallel ranges, at bee = 
of the same great system, are nearly always successlV ae 
formed; and I would add successively formed coastward. na 
illustrates this by reference to the three great ranges. of ie 
North American Cordilleras, viz., the Rocky Mountains, ™e¢ 
Sierras, and the Coast range—and by the several ranges form 
ing the South American Andes. The theory I have preset 
at once explains this fact, and erects it into a law. Its4 
‘necessary result of the theory. . 
_-* ‘This Jour., II, vol. xxii, p. 335. 
