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342 Prof: Beck on Igneous Action, as exhibited in New York. 
_ which now constitute the traps and the various kinds of lava, it 
is difficult to understand, upon this hypothesis, why the fissures 
and cavities of the latter, should contain minerals differing entirely 
in crystalline forms, and in many instances yielding substances 
not known to exist in the rock from which they are said to be » 
derived.* Even granting that the constituents of these minerals 
actually exist in the granite, the chemical mineralogist will be 
slow to believe that, at such distant localities-and in such widely 
separated epochs, the very same, as it were, accidental segrega- 
tion of certain substances should take place. He would be more 
likely to infer that these minerals had previously existed, at least 
in their anhydrous state,—that they had been liquefied by heat, 
and that in their subsequent crystallization they were merely 
obeying the laws of molecular attraction which regulate this 
‘OCess. 
It may be here observed, that the reference of these igneous 
products to ordinary granite is based upon the assumption, that 
“this latter rock not only constitutes the floor of all the strata 
which have been observed, but that it forms the nucleus of the 
globe. But after all, do not the trappean rocks and mine 
show a difference in composition, as well as in the arrangement 
of their constituents? Are not these, as well as our modern lavas, 
the representatives of series of rocks or of materials, whether solid 
or liquid, differing considerably from granite? If they are 80, 
then with the knowledge which we possess in regard to the deep 
seated source of volcanic action, we may conclude that the lavas 
ejected by volcanoes, and the trappean rocks which resem 
them, although found in the cracks and fissures of the most recent 
strata, in fact belong to aseries lower than any which we se¢ 
upon the surface of the earth. And perhaps by a close examina- 
tion of the chemical theory of volcanic eruptions, we shall be 
enabled to comprehend the differences to which we have referred, 
especially if we are willing to admit that the conditions of these 
modern eruptions were different from those which characterized 
the older ones. 
*“ Admitting this prevalence of granitic compounds at the earliest periods, their 
production at more recent epochs shows that the conditions necessary for their for- 
mation continued up to such epochs, though they may have been infinitely mor 
rare, having in a great measure given place to those under which the more com 
mon trappean rocks were produced.”—De la Beche, 475, Am. ed. 
