i+ J. D. Dana— Results of the Earth's Contraction. 
gests.* But with movements in the strata, or progressive plica- 
tions, such as the metamorphic rocks themselves show they 
have experienced, then, according to the principle of the trans- 
formation of motion into heat, first suggested with reference to 
metamorphism by Prof, Henry Wurtz, of New York, in 1866,t+ 
oe Senay. Annee to voleanoes and demonstrated by Robert 
t, Esq., the conditions for metamorphism might be com- 
ie even with comparatively little help from a rise in the 
isogeotherms. This result would certainly follow if the heat 
from motion is great enough, as Mallet appears to show, to pro- 
duce fusion. Such a cause is capable, as others have urged, of 
producing the heat throughout the strata, just where it is needed 
for work. Under it, accumulations of strata of like thick- 
ness and composition would be differently acted upon according 
to the three conditions: (1) the amount of motion, one principal 
source of heat; (2) the thickness of the series of beds undergo- 
ing movement, another source of heat beneath ; (8) the amount 
region of feebly-metamorphic rocks is found to lie side by side 
with one of thoroughly-metamorphic, the strata of the two may 
have ils ally been similar, and of one and the same geological 
orizo 
Metarnoayeiae over large areas is thus one of the direct 
results of the earth’s contraction. Solidification is often only a 
ower stage in the same process; and the reddening of sand- 
stones, as already explained, is frequently involved with it. 
* Vose could hardly have intended to say in place of pressure, the motion pro- 
uced by pressure. For, in one of his paragraphs, he attributes the changes = 
tinctl the e ous pressure generated in the fol of masses of 
” 
rock, t 
depth of which is measured by miles”; and this pressure was that of cae 
sediments alone, while the additional heat required came from a rise i the i 
Decught fa fo smote y Prof. Hunt 7 support of it. Mr. Vose’s views are contained 
in i pubhi 
Jan. 25, 1868. e paper was read at the meeting of the American Association 
at Buffalo, in oe 1866. 
¢ Page 430 of the preceding volume. 
