284 KEMP'S ORE DEPOSITS. 



secondary introductions, such as veins, etc. The former he calls 

 "idiogenites," the latter "xenogenites," basing the names on the 

 familiar Greek terms that run through all our literature. The 

 latter are especially characterized by " crustification," by which 

 term is indicated what has been termed " banded structure," on p. 

 35. The subject of cavities is then taken up, and, while minute 

 pores are stated to be in all rocks, a distinction is made between 

 the larger openings, which originate in a rock mass as a part of 

 its own structure, such as contraction joints in igneous rocks, 

 amygdaloids, and the like, and those induced by outside causes, 

 such as fault fissures. 



The circulation of water through these is next treated : first, 

 surface waters or "vadose" circulations, which descend; second, 

 ascending waters from great depths, such as springs in deep mines, 

 hot springs, etc. The common salts in solution in these latter are 

 tabulated, being of course mostly alkaline carbonates, sulphates, 

 chlorides, etc. The "exotic" metallic admixtures which would 

 bear on the origin of ores are next discussed, so far as possible 

 with analyses of actual cases. The alterations produced by miner- 

 al springs in rocks and the structural relations of the deposits of 

 mineral springs, especially as expressed by " crustification," are 

 then described. This preliminary material clears the way for the 

 general discussion of the origin of ore bodies. The argument run- 

 ning all through the paper is that ore bodies, even when apparently 

 interbedded with sedimentary rocks, are of secondary introduction 

 and, in general for veins, are from deep-seated sources. Precipita- 

 tion from descending solutions and filling by lateral secretion are 

 strongly controverted. 



The discussion of origin follows in its arrangement the follow- 

 ing classification of ore deposits : 



I. Filling of spaces of discission (fissures). 



II. Filling of spaces of dissolution in soluble rocks. 



III. Metamorphic deposits in soluble rocks; in simple sedi- 

 ments ; in crystalline and eruptive rocks. 



IV. Hysteromorphic (i.e., later or last formed) deposits. 

 Secondary deposits due to surface action (i.e., placers, etc.). 



The treatment, both in the introductory pages and in the later 

 discussions, is often strikingly similar to that of this book, and the 

 underlying argument is much the same. The standpoint in both 

 essays is essentially a genetic one, and the main difference lies in 

 the fact that the one is an exposition of an individual's views, 



