Origin of Mountains. 427 
feet, the contracted rocks were measured. 
he 40,000 feet of subsidence required was therefore wholly 
independent of contraction in the stratified sediments. But 
these underlying Archzan rocks were probably crystallized be- 
fore the Paleozoic era began; for in New York and New Jersey 
nian); for in obtaining by measurement this thickness, 40,000 
red 
aleozoic or ear e. As shown in the preceding para 
graph, the contraction, under Prof. LeConte’s principle, must 
have been confined to the underlying rocks; and since e 
subsidence required could not be obtained by the method ap- 
pealed to by Prof. LeConte. Whatever cause, in either of the 
above cases, occasioned the subsidence, it must have been one 
that could do its work in spite of opposition on the part of the 
eat in the rocks themselves or those below. 
Another cause of local subsidence is local cooling beneath, 
accompanying the increasing accumulation of sediments. But 
this idea is too obviously absurd to require remark. 
n the present state of science, then, no adequate cause of sub- 
sidence has been suggested apart from the old one of lateral 
pressure in the contracting material of the globe. 
2. Have elevations been produced directly by lateral pressure ? 
The theory of Prof. Hall denies that mountains are a result 
of local elevations, or of any elevation apart from a general con- 
tinental. This hypothesis I have elsewhere discussed.* 
* This Journal, II, xlii, 205, 252, and this volume, p. 347. 
Am. Jour, Sek tee ety Vou. V, No 30.—Jung, 1873, 
