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[Assembly 
with the thermometer the temperature of the earth below the point 
of no variation, increases, in descending perpendicularly, one de- 
gree for about 80 feet of depth 
The increase of heat of one degree for 80 feet of perpendicular 
depth, or which is the same, 75 degrees for every mile of that 
depth, will give us for a crust of 200 miles in thickness, a tempe- 
rature greater than the medium welding heat of iron. In the 
same ratio, at less than 400 miles, from the known fusibility of the 
components of our crust, we have igneous fluidity as an essential 
permanent condition of our planet, furnishing to those parts of its 
surface, where active volcanoes exist, a constant supply of their 
liquid materials. 
From the fact, that in every part of the globe the composition 
of the crust below those rocks which contain organic remains, is 
crystalline rocks; that those rocks are co-extensive with the whole 
fluid mass. Knowing that the effect of crystallization is expan- 
sion; that to this property water, in freezing, bursts our conduit 
pipes, splits our trees, and rends our rocks; as a consequence too, 
crystallized bodies float upon their fluid material; an expansion of 
a crust, of a few hundred miles in thickness, from the known ex- 
pansion of many mineral substances in crystallizing, gives us an ele- 
vation greater than the height of any mountain known, and to this 
force, as a primary cause, we owe our uplifted rocks, our moun- 
tain chains and parallel fissures. 
Combining with the expansive force of crystallization, the effect 
of its taking place, or operating layer by layer, or rock by rock; 
likewise the tides and currents of the fluid mass, its oscillations and 
undulations; likewise the risings and fallings of an unstable surface, 
and the difference of expansion arising from the heterogeneous na- 
ture of the crust, and we have ample materials, not only for the 
explanation of already collected stores of facts, but for the greatest 
extension to explanatory geological investigation. 
Besides this general cause of the uplifting of strata, others may 
be mentioned; but their operation has been very limited in com- 
parison with that of crystallization. The most obvious one is vol- 
canic action, properly so called; but its results or effects, from 
all known data, are so partial as to admit of no higher agency than 
