Bedded veins may be distinguished from fissure veins by the absence of all traces of a fissure, the want of a banded structure, slickensides, selvages, etc.; from gash veins and the floors of ore which often accompany them, as well as from segregated veins, they are distinguished by the nature of the inclosing rock and the foreign origin of the ore.  Sometimes the plane of junction between two contiguous sheets of rock has been the channel through which has flowed a metalliferous solution, and the zone where the ore has replaced by substitution portions of one or both strata.  These are often called blanket veins in the West, but they belong rather to the category of contact deposits as I have heretofore defined them.  Where such sheets of ore occupy by preference the planes of contact between adjacent strata, but sometimes desert such planes, and show slickensided walls, and banded structure, like the great veins of Bingham, Utah, these should be classed as true fissure veins.

THEORIES OF ORE DEPOSIT.

The recently published theories of the formation of mineral veins, to which I have alluded, are those of Prof.  Von Groddek[1] and Dr. Sandberger,[2] who attribute the filling of veins to exudations of mineral solutions from the wall rocks (i.e., lateral secretions), and those of Mr. S.F.  Emmons,[3] and Mr. G.F.  Becker,[4] who have been studying, respectively, the ore deposits of Leadville and of the Comstock, by whom the ores are credited to the leaching of adjacent igneous rocks.

[Footnote 1:  Die Lehre von den Lagerstatten der Erze, von Dr. Albrecht von Groddek, Leipzig. 1879.]

[Footnote 2:  Untersuchungen uber Erzgange, von Fridolin Sandberger, Weisbaden, 1882.]

[Footnote 3:  Geology and Mining Industry of Leadville, Annual Report, Director U.S.  Geol.  Surv., 1881.]

[Footnote 4:  Geology of the Comstock Lode and Washoe District, G.F.  Becker, Washington, 1883.

It is but justice to Messrs. Becker and Emmons to say that theirs are admirable studies, thorough and exhaustive, of great interest and value to both mining engineers and geologists, and most creditable to the authors and the country.  No better work of the kind has been done anywhere, and it will detract little from its merit even if the views of the authors on the theoretical question of the sources of the ores shall not be generally adopted.]

The lack of space must forbid the full discussion of these theories at the present time, but I will briefly enumerate some of the facts which render it difficult for me to accept them.