Geology and Mineralogy. 83 



Kemp have mentioned the subject, but the present paper is the 

 first to treat it separately and comprehensively. 



After some introductory remarks and definitions a discussion 

 follows of the chemical reactions which take place during the 

 leaching of the mineral contents of the gossan zone; then the 

 chemical processes concerned with mineral deposition in the 

 enrichment zone and of the alterations of various vein minerals, 

 are considered. A more extended description and discussion of 

 the manner of occurrence of secondary enrichments is then entered 

 upon, dealing with the deposits of copper, silver and zinc in prom- 

 inent localities, here and abroad, which have been carefully 

 studied. 



To the material taken from various outside sources Mr. Weed 

 has added much valuable information, gained as a result of his 

 own extensive observations and studies of the ore deposits of the 

 West. 



The conclusions reached are worthy of careful notice and are 

 quoted here in full. Conclusions: "From what has been shown 

 it is concluded that later enrichment of mineral veins is as impor- 

 tant as the formation of the veins themselves, particularly from 

 the economic standpoint. The enrichment is usually due to> 

 downward-moving surface waters, leaching the upper part of the 

 vein and precipitating copper, silver, et cetera, by reaction with 

 the unaltered ore below. In many cases the enrichment proceeds, 

 along barren fractures and makes bonanzas. In others it form& 

 films, pay streaks, or ore shoots in the body of leaner original ore. 

 In still other cases the leaching, transportation, and redeposition 

 are performed by deep-seated upi'ising waters acting upon the 

 vein. 



As a consequence of this, veins do not increase in richness in 

 depths below the zone of enrichment. 



The practical bearing of the phenomena described and the 

 deduction drawn from them will, I think, be apparent to every 

 mining engineer and geologist. If my views be correct, the future 

 of many ore deposits is to be judged in the light of these facts, 

 and the value of the mine must not be based on the pi*esumption 

 that the ore will continue in unabated richness in depth." 



A forthcoming paper, which is promised on the secondary 

 sulphide enrichments of Butte, Mont., will be awaited with no 

 little interest. c. h. w. 



6. Mineralogical Notes. — Number 7 (vol. i) of the Geological 

 Series of Publications by the Field Columbian Museum (pp. 221- 

 240), by Dr. O. C. Farrington, contains an acconnt of several 

 new mineral occurrences and also a description of the fine calcite 

 crystals from Joplin, Missouri. The rare species mesite is noted 

 from a mine near Villa Corona, Durango, Mexico. It occurs in 

 tufts of radiating crystals of flesh-red color. These correspond 

 in angle with the results of Scheibe and show the new forms 

 k (II -0-1 2) and s (946). The following analysis was made : 



