1872.] yaaa (Hunt, 
tween volcanic and plutonic phenomena and great accumulations of 
sediments were insisted upon. It was maintained that the action of 
internal heat upon these would result not only in the softening and 
chemical change of the lower part of these sediments, but also in a 
softening of the underlying floor of older crystalline rocks; thus 
establishing a line of weakness or of least resistance in the earth’s 
crust coincident with that of the great accumulations of sediment. 
From this, it was claimed, it would result that the wrinkling or cor- 
rugation of the earth’s crust due to a contracting nucleus would be 
determined along the lines of great sedimentation. 
The source of heat required to produce these effects was assumed 
by Herschel (as previously suggested by Babbage) to be the incan- 
descent nucleus of the globe, a view in which the speaker had ac- 
quiesced. Keferstein, on the contrary, rejecting an internal source of 
heat, had supposed it to be generated by a chemical process in the 
sediments, which he compared to a fermention. Very recently Le 
Conte has proposed a view which unites the two, supposing the inter- 
nal heat to set up a chemical action in the buried sediments, which 
once commenced, may augment their temperature even to the fusing 
point. It was maintained by Dr. Hunt that the chemical actions 
which would take place in the buried sediments would be of a nature 
rather to absorb than to give out heat, and such views were hence to 
‘be rejected. It seems, however, probable that the seat of volcanic 
activity is to be found at depths where the heat derived by conduc- 
tion from the nucleus would not be adequate to produce the effects 
required, and there still remained the hypothesis that the heat might 
be in part generated by local physical causes. This was, it is be- 
lieved, first suggested by a member of this Society, Mr. George L. 
Vose, in his able and scholarly little book, entitled Orographic Ge- 
ology, published in 1866. He there, while recognizing with Sorby the 
conversion of mechanical force into chemical action, insists that ‘‘the 
enormous pressure generated by the folding of masses of rocks, the 
depth of which is measured by miles,” is an agent capable of pro- 
ducing great changes, and declares the causes of the conversion of 
sediments into plutonic rocks like granite to be “mechanical compres- 
sion, with the heat and chemical action which proceed therefrom ;” 
adding, in a note, in allusion to the view which explains these 
changes by heat conducted from beneath, ‘‘we should prefer to get 
the heat needed by the compression which accompanies the distur- 
bance of the strata where metamorphism occurs.” [Orographic Ge- 
