58 On the Minerals of Trap and the allied Rocks. 
bed of an ocean? Even at a depth of three miles, the waters 
press upon the bottom with a force equivalent to a million of 
pounds to the square foot ; and with such a forcing power above, 
can we set limits to the depth to which these sea waters—mag- 
nesia and soda solutions—will penetrate? Will not every cav- 
ern, every pore, far down, be filled under such an enormous 
pressure? Leta fissure open by an earthquake effort, and can 
we conceive of the tremendous violence with which the ocean 
will rush into the opened fissure? Let lava ascend, can we have 
an adequate idea of the effect of this conflict of fire and water? 
The rock rises, blown up with cavities like amygdaloid, and 
will a long interval elapse before every air cell will be oceupied 
from the incumbent water? Suppose an Hawaii to be situated 
beneath the waves, pouring forth its torrents of liquid rock ;—this 
island contains about five thousand square miles, which is less 
than the probable extent of many a region of submarive eruption ; 
—suppose, I say, the fires were opened and active over an area of 
some thousands of square miles—are there no effects to be dis- 
covered of this action? ‘There is no geologist that pretends to 
deny the premises—the fact of such submarine eruptions, the 
ocean’s pressure, the effect of fire in heating water, and in giving 
it increased solvent power; and why should they not reason upon 
the admitted facts, and study out the necessary consequences ? 
Surely, if there have been effects, we might expect to see some 
of them manifested in the cavities of the ejected rocks, which 
were opened at the time to receive the waters and any depositions 
they might be fitted under the circumstances to make. 
We are led by these considerations to another point in connec- 
tion with this subject: the probable condition under which the 
different amygdaloidal minerals have been formed. Have they 
all proceeded from heated solutions, or all from cold solutions? 
or can we distinguish some which are indubitably of one or the 
other mode of formation? 
Bearing on these questions, we notice such facts as are afforded 
by the condition and relative positions of the minerals in geodes. 
And I would here acknowledge my obligations to the valuable 
memoir, before alluded to, by Messrs. Jackson and Alger. The 
paucity of information on this subject, to be found in the various 
accounts of similar rocks by other writers, is surprising. Even 
where special pains have been taken to describe the mineral spe- 
cies, the relative positions of the minerals is very seldom noted. 
