•# PALEONTOLOGY OF NEW-YORK. 



Now it seems to me that the proposition here stated, and the result which follows, 

 tend to sustain the views I have advanced. 



If this deposit C becomes so great as to disturb the equilibrium of pressure, and 

 the effects upon the yielding mass below are such as to displace a portion of the 

 same, then the strata which were originally deposited in a horizontal position must 

 become curved. The area of deposit could not have acquired an equal accumulation, 

 and there would be little or no depression towards the thinning margins. Tiien if the 

 accumulation should go on to many thousands of feet in thickness, and the ocean bed 

 be depressed accordingly, we should have a greater deflection of the strata from the 

 original horizontal position; and, as I conceive, tliis depression must be accompanied 

 by folding or plication, unless, as Herschel suggests, the support may give way, 

 and the mass be plunged into the fluid beneath, wliich would cause a rush of this 

 matter upwards. This condition, however, as I believe, happens only when the 

 accumulation is very rapid, and probably often not widely extended. 



I am not quite able to agree that the subversion of the equilibrium of temperature 

 is more important (in tlie outset at least) than the subversion of the equilibrium of 

 pressure, though I conceive that its ultimate effects are more important and more 

 permanent ; since, as he says, every continent depressed has a tendency to rise 

 again, and, as I understand, this results in a great measure from a restoration of the 

 equilibrium of temperature. It is this ultimate rising of continental masses, that I 

 contend for, in opposition to special elevatory movement along the lines of moun- 

 tain chains. 



In a letter to Sir Roderick Murchison, following the one above cited. Sir John 

 Herschel discusses this subject still farther, showing conclusively that the deposi- 

 tion of sediments, subverting the equilibrium of temperature and of pressure, pro- 

 duces the result, as a natural and necessary consequence, which even at this day is 

 too often attributed to excessive or abnormal influence of the heated or fused interior 

 mass. " Let strata be deposited,''^ he says, and we have all the required condition 

 for producing metamorphic rocks. 



Reasoning from a different point, and with a different class of facts under con- 

 sideration, I have arrived at tlie conclusions before given; and, farther, that without 

 great accumulations of strata ( perliaps a legitimate deduction also from the argu- 

 ments of Herschel), no important or extensive metamorphism can take place. 



In the preceding pages, I have often used the tenn current linti, or accumulation along the current linet, I 

 might, more properly in most cases, hare used the term coast lines or shore lines; these being doubtless the zones of 

 great accumulation, and in this view we may have hod a coast line nearly parallel and coextensive nith the Appalacbioo 

 chain. This fact, bowerer, if ascertained) would not conflict with the faeU or argumenUi I have adduced. 



