GEOGNOSY AND GEOLOGY. 133 
carbonate of lime, veins of gypseous spar in compact gypsum, We., have 
been filled by infiltration from the accompanying rock. This, however, 
may not be said in regard to metallic ores, or of such veins as contain 
native metals, since we cannot understand what medium could have 
dissolved these substances, which, besides, we do not find in the accom- 
panying rock. 
The principal theories, according to Von Herder, may be distributed 
under four heads: 
1. Congeneration Theories, which consider the veins as having been 
formed contemporaneously with the accompanying rock, and not by 
subsequent filling up. This antiquated view has too much against it to 
require any special refutation. . | 
2. Theories of Lateral Secretion. According to these the contents of 
veins are to be considered as leachings or deposits of solutions of the 
accompanying rock. Metallic substances are supposed to have been 
deposited from salts or other combinations upon the solid walls of the veins 
by means of galvanic processes. That the component particles of calc 
spar, gypsum, tale, and of geolitic and silicious minerals, may have been 
dissolved in water from the accompanying rock, and deposited as such 
minerals on the walls of the vein by evaporation of the water, is, as above 
remarked, very probable; but the occurrence of metallic minerals can 
hardly. be explained in this manner. This theory is thus very one- 
sided. 
3. Theories of Descent. These were earnestly supported by Werner, 
who endeavored to accommodate all facts to the prevalent Neptunian 
hypothesis. He considered the vein mass to have been deposited in 
previously existing cracks, just as the stratified rocks were deposited from 
water. Single vein masses have unquestionably been formed in this way, 
but they are of quite unfrequent occurrence. To this view it may be 
objected, that older and newer, primary and secondary minerals, may be 
distinguished in the same vein; that it has not yet been proved that all 
veins wedge out below, the contrary being capable, in many instances, of 
complete demonstration ; that the same matter ought to have been deposited 
in other situations than in veins alone, which has not been known to occur. 
Conversions and metamorphoses have unquestionably been produced in the 
upper portions of veins, by the penetration of small quantities of water, as 
shown in the formation of carbonate of lead, sulphate of lead, and phosphate 
of lead, as well as chlorine combinations of lead, from galena, &c. 
Nevertheless, this theory, thus restricted, is not accepted by the disciples 
of Werner. 
4. Theories of Ascent. These endeavor to prove a filling from below 
upwards. The ascent may take place in various ways, either by injection, 
by penetration of the vein mass in a molten condition, by infiltration, by 
deposit on the walls from ascending mineral waters, and by the sublimation 
or deposit of solid particles from a gaseous state of aggregation, produced 
by a diminished temperature. Formations of this character we may see 
going on now before our eyes, and especially the sublimatior in volcanic 
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