L58 Scientific Intelligence. 



amount of work done. G. II. Eldridge contributes a paper 

 (pp. 219-452) on the Asphalt and Bituminous Rock Deposits of 

 the Tinted States, in which is discussed in detail the nature of 

 the materials and their mode of occurrence. 



Twenty-second Annual Report, 1900-0 1 , Pt. II. Ore Depos- 

 its, 865 pp., 82 pis., 130 figs. The old Tungsten Mine at Trumbull, 

 Conn., is described by Prof . Hobbs. (See this Journal, xiv, 72.) 

 A Preliminary Report on the Lead and Zinc Deposits of the 

 Ozark Region is made by H. F. Bain, with an Introduction by 

 C. R. Van Hise, and chapters on Physiography and Geology 

 by Geo. I. Adams. Mr. Bain summarizes his conclusions as to 

 the genesis of these ore deposits somewhat as follows : The metals 

 were originally precipitated from shallow seas by organic matter 

 at the time of the formation of the dolomitic limestones of the 

 Cambro-Silurian, and were afterwards concentrated and redepos- 

 ited by the action of underground waters in fractured or brecci- 

 ated zones in the Carboniferous limestones, being altered later 

 by superficial agencies, with oxidation and frequently notable 

 enrichment. The Ore Deposits of the Rico Mountains, Colorado, 

 are described by F. L. Ransome. The ore of the Rico district, 

 which is mostly argentiferous galena, occurs in a number of dif- 

 ferent formations, as in fissure veins, in bedded or blanket veins, 

 in replacements in limestone and in stocks. Of these types the 

 second has been the most productive. The bulk of the ore has 

 been found in Carboniferous sedimentaries which lie in the cen- 

 tral portion of the domical uplift of the Rico Mountains. The 

 area has produced about $10,000,000 worth of ore in the twenty- 

 one years of its existence. At present little mining is being 

 done, and the future of the district is somewhat problematical. 

 Geology and Ore Deposits of the Elkhorn Mining District, 

 Montana, is the subject of a paper by Walter Harvey Weed 

 and Joseph Barrell. The Elkhorn district lies on the border 

 between a great granite area and an area of folded sedimentaries. 

 The ore bodies are saddle deposits formed in pitching arches be- 

 neath a bed of impervious slate and in a dolomite marble. The 

 deposits were mainly due to the gradual replacement of the dolo- 

 mite by the substances brought up along a zone of crushed rock 

 by uprising siliceous waters. The metallic contents of the deposit 

 are believed to have come from a gabbro intrusion underlying 

 the limestone. The ore was chiefly a silver carrying smaller 

 values in gold, lead and copper, and was free milling and rich 

 near the surface, but became refractory and of poorer grade 

 in depth. Work in the district was discontinued in 1900. 

 The Gold Belt of the Blue Mountains of Oregon is described 

 by Waldemar Lindgren. This district, situated in the north- 

 eastern part of Oregon, forms the most important gold field of 

 the state, yielding at least three-fourths of the total output. The 

 Blue Mountains consist of several cores of old sedimentaries, sur- 

 rounded by late lavas and igneous rocks of varying types. It is 

 in these old cores that the greater part of the gold and silver 



