Igneous Origin of some Trap Rocks. 129 
swept away in the progress of time, and that they were subjected to 
a vast pressure of solid materials, and not improbably of the ocean; 
the ancient ocean which enveloped the globe, before it attained its 
habitable condition. 
f fire were the agent, it is not now necessary to stop to account 
for it ; for its existence at the present moment, and in all ages, is an 
anqiteniadsbls fact, and must be. admitted, whatever theories of its 
origin we adopt or reject, and no geologist will question the original, 
or at least early submergence, of our planet under a deep ocean. 
If then we suppose that the materials of the trap rocks were melted 
below, and were forced upward through the incumbent strata, either 
from fissures or vents, and that upon those superior strata, the ocean 
itself was also incumbent, we have all the conditions necessary for 
the solution of this problem.* Had the trap rocks been erupted into 
day light like currents of lava, there would be no reason why they 
should not exhibit all the variety of appearance that belongs to lavas ; 
but, if only forced through, and among superior strata, or even if 
forced quite through them, but still remaining under the pressure of 
many miles of ocean ; they would congeal under enormous pressure, 
and of course would be long in cooling, and would in the main as- 
sume the stony or rocky, rather than the vitreous character. Sir 
James Hall, and Mr. Gregory Watt proved, a good many years since, 
that trap rocks, if melted and cooled very slowly, and under press- 
ure, do, in fact, reassume the stony and subcrystalline appearance ; if 
rapidly and without pressure, they become vitreous, and the same 
pieces may be made to pass from one stage to the other at pleasure ; 
the slag becoming rock again, and the rock again slag T the same 
fact is true also, of acknowledged lavas. 
In the case of the Hartford quarry, if we suppose that the melted 
trap came in contact with the argillaceous sandstone, still charged 
with abundant moisture, which the evident cireumstances of its depo- 
sition would necessarily imply,t and replete too with carbonic acid in 
* All compound rocks are fusible, and as we have every reason to believe are ac- 
tually melted in volcanos: trap is fusible in our furnaces, and bottles were some 
trap, so that it flowed and congealed on the grates of the furnace in stalactites. 
t I saw the specimens of Sir James Hall, (father of Capt. Basil Hall, the celebrated 
traveller in America.) They were a by Dr. Hope, at one of his public lec- 
“airs his discussion of the Huttonian theor, 
any proof were wanting that RE TS! class of reeks 3 was laid down under water, it 
is god In quarrying the coarse conglomerate sandstone, (a part of —— 
Vor. XVIL—No. 1. 17 
