AMERICAN GEOLOGY DECADE OF 1870-1879. 559 



He showed that, were a mass of sediments 10,000 feet in thickness 

 subjected to horizontal pressure and crushing sufficient to develop 

 well-marked cleavage structure, a breadth of 2£ miles would be crushed 

 into 1 mile, and 10,000 feet thickness would be swelled to 25,000, mak- 

 ing an actual elevation of the surface of 15.000 feet. He, therefore, 

 felt justified in asserting that the phenomena of plication and of slaty 

 cleavage demonstrated a crushing together horizontally and an upswell- 

 ingof the whole mass of sediments, the ups welling produced by this cause 

 alone being sufficient to account for the elevation of the greatest moun- 

 tain chains. 



Hall's theory, previously noted (p. 499), he regarded as wholly failing 

 to explain the actual process by which the chains had been formed; 

 and, taking into account the breadth of the Appalachians (at least 100 

 miles), he showed that the gentleness of the supposed convex curve of 

 Hall would not produce the amount of crushing necessary for the for- 

 mation of the immense plication. 



Moreover, he pointed out the fact that sedimentation and subsidence 

 were going on together, and, therefore, that the upper surface was 

 probably never convex at all, but nearly or quite horizontal all the 

 time. Subsidence under such conditions might produce horizontal 

 tension -or stretching of the lower strata, but could not produce the 

 crushing and plication of the upper. 



To Whitney's idea that plication was the result of the subsidence of 

 a mountain axis he likewise took exception, and contended that chains 

 and ranges were, beyond question, produced by horizontal thrust, 

 crushing together the whole rock mass and swelling it up vertically, 

 this thrust being the necessary result of secular contraction of the inte- 

 rior of the earth. In other words, "mountain chains are formed by 

 the mashing together and upswelling of sea bottoms where immense 

 thicknesses of sediments have accumulated, and as the greatest accu- 

 mulations usually take place off the shores of continents mountains are 

 usually formed b} r the uppressing of marginal sea bottoms." The sub- 

 marine ridges and hollows shown by the soundings of the Coast Survey 

 to exist along the course of the Gulf stream, extending from the point 

 of Florida to the coast of New England, he felt might be true subma- 

 rine mountain ranges now in course of formation by the processes 

 already described. 



Referring to the subject of metamorphism of rocks, as shown in 

 mountain chains, he argued as follows: Supposing sediments accumu- 

 lating along the shores of a continent. The first effect is lithitication, 

 and, therefore, increasing density, causing contraction and subsidence 

 pari passu with the deposit. Next, if the sedimentation continue, 

 aqueo-igneous softening or even melting would follow, not only of the 

 lower portions of the sediments themselves, but of the underlying strata 



