22, T. S. Hunt on Volcanic Action. 
st of no great thickness was formed, which rests upon the 
all uncongealed nucleus. The second ‘hypothesis, maintained 
Hopkins and by Poulett Serope, supposes solidification to 
have commenced at the center of the liquid globe, and to have 
advanced toward the circumference. Before the last portions 
became solidified, there was produced, it is conceived, a con- 
dition of imperfect liquidity, preventing the sinking of the cooled 
eavier particles, and giving rise to a superficial crust, from 
which solidification would proceed downward. There would 
thus be a between the inner and outer solid parts, a =f Se 
existence is thus conciliated with he pe ee facts of a flexible 
crust, and of liquid ignited matters beneat 
Ho opkins, in the discussion of this question, insisted upon the 
fact established by his experiments, that pressure favors the 
cation of matters which, like ‘rocks, ass in melting to a 
leat dense condition, and hence concludes that the pressure ex- 
isting at great depths must have induced solidification of the 
molten mass at a temperature at which, under a less pressure, it 
would have remained liquid. Mr. Scrope has followed this At 
by the ingenious suggestion that the great pressure upon p 
of the solid igneous mass may become relaxed from the eft of 
local movements of the earth’s crust, causing portions of the 
solidified uae to pass immediately into the liquid atnte, thus 
iat rise to eruptive rocks in regions where all before was 
igneous Aisa In this Conbauolbite it is curious to peng that, 
as pointed out by Mr. J. Clifton Ward, in the same Magazine — 
for Dece ier: (page 581), Halley was led, from the study of ter- _ 
restrial magnetism, to a similar hypothesis i sup osed the 
rust, and others in an interior mass, oh ated from. the a 
sli i envelope by a fluid medium, and revolving, by a very 
See Scrope on Voleanos, and his communication to thi ——— : 
for Dee, 1868, : s 
