as gia RA hs i a a a 
Metamorphism. 13 
continental mass beyond it, and to the weakness produced in 
its crust in the manner explained, became, under the continued 
lateral pressure and the gravity of the geanticlinal, a scene of 
catastrophe and mountain-making after the manner described. 
The principle here brought in, that the weakening of the crust 
through the rise of the isogeotherms was one occasion of the 
catastrophe, is made of prominent importance by Professor 
LeConte (vol. iv, p. 468), though by a somewhat different 
method. ° 
The geological facts thus far gathered have not yet proved 
that there was a geanticlinal on the Pacific border (like that of 
the Atlantic), as a counterpart to the geosynclinals in progress ; 
but the evidence may be looked for with confidence. 
Ill METAMORPHISM. 
the ascending isogeotherms, must have been before their dis- 
turbance, as calculated by Prof. LeConte, not less than 800° F., 
and much above this, if more heat escaped from the earth then 
than now. Thus seven miles of accumulations were not sufli- 
cient to bring about metamorphism or erystallization even in 
ahbabs beyond that of ordinary 
It seems certain, therefore, that this method of obtaining the 
heat, b blanketing the surface with strata, is not sufficient. 
volume of this J ournal, can heat be derive from simple pres- 
Sure or “mechanical compression,” as the language of Vose sug- 
nN The arguments here presented are the same that I urged in this Journal, in 
alii, p. 252, 1866. 
