240 Messrs. Jackson and Alger on the 
and by a subsidence of the tenacious mass below, containing 
the other hemisphere. The tubes are often bent at right 
angles, as if the rock had been subjected to an alternate ir- 
regular elevation and depression. The occurrence of native 
copper in a similar cavity, a few miles to the east of this 
place, might probably be adduced as evidence that the pro- 
duction of this rock was attended with heat. In the instance 
referred to, there was a crystal of green analcime attached toa 
filament of native copper, which, projecting from the rock, prob- 
ably served it as a nucleus on which to crystallize. The crystals 
of heulandite &c. were doubtless deposited subsequently to the 
formation of the cavities, as the incrustation always received its 
impressions from the irregularities of the tube, and never left any, 
although it received an indentation from the slightest prominence 
in the rock. The only way in which we can account for these 
cavities, on the supposition that the rocks were of aqueous origin, 
would be, to suppose the upright tubes to have been produced 
by the ascent of some elastic gas; but as the cavities are soon 
arrested by a dense superincumbent rock, and have no outlet, 
and at the same time diminish in size as they ascend, there is 
reason to suppose the cavities to have been produced by some 
condensible elastic fluid, as steam. Their position shows the force 
which produced them to have acted in a direction up and down, 
and their irregularities perhaps indicate the rising and falling of 
the liquid mass. 
The inadequacy of any hypothesis to explain these appear- 
ances, if founded on the aqueous origin of the trap, is clearly 
shown, we think, by the evidence we have in favor of the oppo- 
site theory; a theory which satisfactorily explains the peculiari- 
ties referred to, and which derives no little support from, if it is 
