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On the Minerals of Trap and the allied Rocks. 49 
i * 
Art. VIL.—Origin of the constituent and adventitious Minerals 
of Trap and the allied Rocks; by James D. Dana. 
(Read before the Association of American Geologists and Naturalists, May, 1845.) 
In the remarks which I have the honor to submit to the Asso- 
ciation at this time, it will be perceived that I pass over in part 
the same ground, and appeal in some instances to similar facts 
with those considered by Prof. Beck in his valuable memoir read 
two years agoat Albany. Without making myself his opponent, 
which position I would entirely disclaim, I have simply en- 
deavored to hold up the subject in another point of view, hoping 
that the truth, with whomsoever it be, will the sooner claim its 
place among the facts of geological science. It will be remarked 
also, that the views presented bear closely upon those proposed 
by me at the session of this Association at Albany. 4 
The minerals of trap and the allied rocks may be arranged in 
two groups. 
1. Those essential to the constitution of the rock, or intimately 
disseminated through its texture. 
2. Those which constitute nodules or occupy seams or cavities 
in these rocks. 
Of the first group, are the several feldspars, with augite, horn- 
blende, epidote, chrysolite, leucite, specular, magnetic and titanic 
iron; and occasionally Hauyne, sodalite, sphene, mica, quartz, 
garnet and pyrites. Of the second group are quartz, either crys- 
tallized or chalcedonic, the zeolites or hydrous silicates, Heuland- 
ite, Laumonite, stilbite, epistilbite, natrolite, scolecite, mesole, 
Thomsonite, Phillipsite, Brewsterite, harmotome, analcime, cha- 
bazite, dysclasite, pectolite, apophyllite, Prehnite, datholite, to- 
gether with spathic iron, calc spar and chlorite. Native copper 
and native silver might be added to both groups, yet they belong 
more properly to the latter. To the same also might be added 
sulphur, and the various salts that are known to proceed from 
decompositions about active volcanoes, including the crystalliza- 
tions of alum, gypsum, strontian, &c.; but these more properly 
form still a ¢hzrd group, and being well understood, will not come 
under consideration in the remarks which follow. 
We observe with regard to the minerals of the first group, that 
they are all anhydrous—that is, contain no water. In this re- 
Vol. xt1x, No. 1.—April—June, 1845. 7 
