258 The American Geologist. April, 1894 
tally upon the forms of the cavities or fissures; but it is 
clearly recognized, as already pointed out, that with increas- 
ing knowledge of the chemistry of vein formation the mode 
of filling will take precedence as a basis for the classification, 
the present arrangement being regarded as provisional. Not 
■only the character of the mineral solutions, but their sources, 
whether descending, lateral (lateral secretion veins), or as- 
cending, should be considered in the true classification of 
veins. The advocate of either source to the exclusion of the 
others ought to appear as archaic now as would an out-and- 
out plutonist or neptunist: for this is the day of the recogni- 
tion of the kernel of truth in every theory. We are recognizing 
more and more clearly that nature has worked in diverse 
modes to the same general end, and that a complex class of 
phenomena cannot, as a rule, be referred to a single simple 
cause. Posepny has properly emphasized the distinction be- 
tween the superficial and the deep-seated aqueous circulation, 
and he is undoubtedly right in relegating the phenomena of 
vein formation chiefly to the domain of the latter. But in his 
enthusiasm as an ascensionist he has probably gone too far 
and referred to ascending currents deposits that may be more 
readily explained by lateral secretion or descending currents. 
During the filling of a cavity, the mineral solutions may or 
may not penetrate and impregnate the walls; and this impreg- 
nation, when it occurs, may or may not be metasomatic. Thus 
the same continuous deposit may combine a vein and an im- 
pregnation, or a vein and a substitution deposit, or all three: 
and the vein is in many cases the least important part of the 
combination, having simply supplied a channel for the impreg- 
nating and replacing solutions. Similarly veins may or may 
not occur on or near igneous contacts, although, as others have 
pointed out, all deep veins are contact deposits with reference 
to the igneous interior of the earth. These distinctions, as 
well as the source and nature of the solutions, and the mode 
of origin of the cavities, should be recognized in a complete 
and detailed classification of veins. But it is deemed suifi- 
cient to simply refer to them here, and thus, incidentally, to 
explain the absence from the outline scheme here proposed of 
the so-called contact veins. 
In a classification of veins filling secondary cavities in ac- 
