72 ON SOME POINTS IN DYNAMICAL GEOLOGY. [VII. 



traction of the mass. A further and very important result of 

 this accumulation there pointed out was by the softening of the 

 underlying floor, or the " bottom strata to establish lines of weak- 

 ness or of least resistance in the earths crust, and thus determine 

 the contraction which results from the cooling of the globe to ex- 

 hibit itself in those regions, and along those lines where tlie ocean's 

 bed is subsiding beneath the accumulated sediments." Hence, 

 I added, "We conceive the subsidence invoked by Mr. Hall, 

 though not the sole nor even the principal cause of the con ULU- 

 tions of the earth's strata, is the one which determines their 

 position and direction by making the effects produced by the 

 contraction, not only of sediments but of the earth's nucleus 

 itself, to be exerted along the lines of greatest accumulation." 

 (Ante, page 57.) As further results of this process of accumu- 

 lation, I also asserted " the metamorphism of sediments in situ, 

 their displacement in a pasty condition from igneo-aqueous fu- 

 sion as plutonic rocks, and their ejection as lavas, with attend- 

 ant gases and vapors." (Ante, page 16.) 



With these conclusions, enunciated in 1858 1861, we may 

 compare those arrived at by Professor LeConte in his recent 

 essay, where he recognizes as consequences of the heating of 

 great thicknesses of sediments accumulated along the shores of a 

 continent, a process of condensation in the lower strata, result- 

 ing in " contraction and subsidence paripassu with the deposit," 

 followed by " aqueo-igneous softening or even melting, not 

 only of the lower portion of the sediments themselves, but of 

 the underlying strata upon which they were deposited; the sub- 

 sidence probably continues during this process. Finally, this 

 softening determines a line of yielding to horizontal pressure, and 

 a consequent upswelling of the line into a chain. Thus aiv 

 accounted for, first, the subsidence, then the subsequent upl> 

 and also the metamorphism of the lower strata." Beneath < 

 giv.-it line of sediments there will moreover be found, according 

 to him, a reservoir of sedimentary material in a state of more or 

 less complete fusion, in which volcanic phenomena have their 

 seat. The reader cannot fail to see that these views are identi- 

 cal with those which I have so long advocated. 



