578 



SCIENCE. 



[N. S. Vol. XIV. No. 354. 



even making a former low-grade body of suflfi- 

 cient value to work. 



It may be concluded that later enrichment 

 of mineral veins is as important as the forma- 

 tion of the veins themselves, particularly from 

 an economic standpoint. In many cases the 

 enrichment proceeds along barren fractures and 

 makes bonanzas. The enrichment is usually 

 due to downward-moving surface waters, leach- 

 ing the upper part of the vein and precipitating 

 copper, silver, etc., by reaction with the un- 

 altered ore below. As a consequence of this, 

 veins do not increase in richness in depths be- 

 low the zone of enrichment. 



In the Transactions of the American Institute 

 of Mining Engineers, Volume XXX., which is 

 just being distributed, Mr. S. F. Emmons has a 

 paper bearing upon this same subject of ' Sec- 

 ondary Enrichment of Ore Deposits.' The au- 

 thor draws upon his wide experience in calling 

 attention to the many cases of secondary en- 

 richment. The main theme discussed is summed 

 up in the opening paragraphs, when he says 

 that, ' admitting fully the general truth of the 

 statement that the descending surface waters 

 exert an oxidizing action, and hence that oxida- 

 tion products within reach of the surface waters 

 are the result of alteration by the latter, I have 

 been led to believe, by observations now ex- 

 tending over a considerable number of years, 

 that, under favorable conditions, the oxidation 

 products may be changed back again into sul- 

 phides and redeposited as such, thus producing 

 what may be called a sulphide enrichment of 

 the original deposits. * * * Being rather a 

 searcher after facts than a theorist, I am not 

 deterred from accepting what may appear to me 

 the correct reading of observed facts because it 

 seems tocontradict generally accepted theories. ' ' 



The same volume of the Transactions contains 

 a practical application of Mr. Weed's theory to 

 Montana deposits, under the title of the ' En- 

 richment of Gold and Silver Veins.' Attention 

 is especially called to the dependence of such 

 enrichments upon the presence of iron sulphide 

 in the primary ore, and to the structural fea- 

 tures which control the circulation of the en- 

 riching solutions below water-level. The pro- 

 cess may be briefly described as follows. 

 Leaching out of the metals from the portion of 



the vein lying above ground-water level is to 

 be considered as the main source of the enrich- 

 ing materials. The leaching is due to superfi- 

 cial alteration, and leaves the iron as a gossan, 

 while the waters carrying the gold, silver, 

 copper and other metals in solution trickle 

 downward through the partially altered ores 

 into cracks and water-courses which penetrate 

 the ore body below the water-level. In weath- 

 ering, the sulphides oxidize according to their 

 relative aflinity for oxygen and inversely as 

 their affinity for sulphur. It is inferred from 

 the evidence that ore bodies lacking in iron 

 pyrite will not show enrichment, thus explain- 

 ing the absence of any such phenomena in the 

 pure silver-lead bodies of the Coeur d'Alene 

 district and elsewhere. 



Charles R. Keyes, 



RECENT ZOO-PALEONTOLOGY. 



VERTEBRATE PALEONTOLOGY AT THE CARNEGIE 



MUSEUM. 



During the past summer three parties from 

 the Department of Vertebrate Paleontology of 

 the Carnegie Museum have been operating in 

 our western fossil fields under the direction of 

 Mr. J. B. Hatcher, the Museum's curator of 

 vertebrate paleontology. One of these parties, 

 in charge of Mr. O. A. Peterson, was sent 

 to northwestern Nebraska to examine the 

 Oligocene and Miocene deposits of that region. 

 The work carried on by this party has been 

 quite successful, — as might be expected from 

 any party in charge of so experienced and 

 skilled a collector of vertebrate fossils as is Mr. 

 Peterson. Among other material secured may 

 be mentioned as of especial value, skeletons 

 of Hoplophoneus, Daphgenus, Oreodon, Procame- 

 lus and Merycochoerus, all, it is believed, suffi- 

 ciently perfect to admit of mounting as com- 

 plete skeletons. A second party, in charge 

 of Mr. C. W. Gilmore, was despatched to 

 southern Wyoming to continue the work which 

 has been carried on by the Museum for the past 

 two years in the Jurassic deposits at Camp 

 Carnegie, on Sheep Creek, in Albany Co., 

 Wyoming. This party has met with the usual 

 success attending the two previous expeditions 



