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[Assembly 
or masses, from having great thickness, when compared with their 
other dimensions, of which the gypsum at the outlet of Seneca lake 
is an example for a stony mineral, and the lead of Missouri for a 
metallic one. 
Lastly. From the disposition of another class called stockwerkes 
by the Germans, being a cluster of little veins, of which the sep- 
taria of Lake Erie, were the cracks or fissures filled with metallic 
minerals, would give a perfect idea, only on a small scale. In all 
these different modes of appearance of the metallic minerals, I 
again repeat, that their origin and that of the stony materials of 
the rocks in which they occur, are one and contemporaneous. 
The common occurrence, likewise, in western New-York, Ohio, 
Kentucky, &c. of galena and blende in the body of the rock, imd 
in the cavities once occupied by fossil bodies, shews a common ori- 
gin. So likewise of the various copper ores in the red sandstone 
of New-Jersey and Pennsylvania; numberless are the localities of 
these ores in that rock where they form a part of the mass, and 
but one or two instances only are known where regular veins ex- 
ist So also, like instances are innumerable in every part of the 
world; but the former alone were chosen, in consequence of being 
more particularly known to us all. 
Of the second position, that of the crystallizable mineral or mine- 
rals of the rock, forming the matter of the vein, we may say the 
evidences from individual instances are without number. 
In the innumerable veins of gneiss rock, we have its three con- 
stituents, quartz, feldspar and mica, in larger particles than in the 
rock, and so arranged as to form granite, but of a kind altogether 
peculiar to the rock, and often embracing those minerals which ex- 
ist disseminated in the rock. In granite, veins are equally nume- 
rous, and of granite likewise, but destitute of the accompanying 
minerals of the gneiss. In all quartzose rocks, the veins are of 
quartz. So in limestone, the matter of the veins is carbonate of 
lime. If the rock be of argillite, containing carbonate of lime, 
the veins will be of quartz, and the latter mineral. These instan- 
ces suffice, though more might be adduced, to show that a marked 
connexion exists between the crystallizing mineral composition of 
the rock and the vein, a cause and effect, a dependence that must 
be the result of a general law, and not an arbitrary effect, as is 
instanced in all volcanic dykes, and would be the case, were the 
