466 Scientific Intelligence. 



these leaves, showing them to represent a flora of Miocene age made 

 up of conifers, oaks, etc., and including several new species. 



II, Gold and silver veins of Silver City, De Lamar and other 

 mining districts in Idaho, by W. Liistdgren (pp. 65-256, pis. 

 *<-35). This begins with a sketch of the general geology of 

 western central Idaho, accompanied by a geologic map, based in 

 part on actual surveys made by the author and in part on 

 reconnaissance work. The map shows a central area of post- 

 Carboniferous granite of great size, bordered on the east by 

 Carboniferous beds in which it has produced contact metamorph- 

 ism. The Snake River runs through the southern and, turning to 

 the north, the western portions of the area and along its course 

 is bordered by immense outflows of basalts, some of Miocene, 

 others of Pliocene age. The Silver City and De Lamar district 

 is in this southern part on a granite ridge which rises above the 

 flood of basalt and rhyolite. The gold and silver veins of this 

 district, their mode of occurrence, the associated minerals, the 

 individual mines, etc., are carefully and fully described. In the 

 same manner the author gives an account of the Wood River 

 district, where the silver-lead ores occur in veins cutting the Car- 

 boniferous beds. At Florence and Warren, situated in the great 

 granite area, the veins are gold quartz and some placer mining is 

 done. In the Seven Devils district the ore is copper in the con- 

 tact zone of the granite mass with the Carboniferous beds on its 

 western side. The ores are bornite and chalcopyrite and are sup- 

 posed to have been deposited by pneumatolytic processes. The 

 paper contains a wealth of careful observations on a large num- 

 ber of ore deposits and is a most important contribution to the 

 study of ore deposits in general. 



III, Geology of the Little Belt Mountains of Montana, with 

 notes on the mineral deposits of the Neihart, Barker, Yogo and 

 other districts by W. H. Weed, with a report on the petro- 

 graphy of the igneous rocks of the district by L. V. Pjesson. 



The Little Belt Mountains are an anticlinal uplift of a rather 

 broad, even character. In the central portion erosion has dis- 

 closed the fundamental Archean gneisses and schists upon which 

 the later sediments lie. These range through the Belt formation 

 (here having a considerable local development and supposed to 

 be of Algonkian age), the Cambrian, Siluro-Devonian, Carbon- 

 iferous, up to the Cretaceous forming the outer foot hills, slopes 

 and boundary plains of the area. The streams rising in basins 

 of Belt or Cambrian shales pass through deep and narrow can- 

 yons or gateways of Carboniferous limestone. Chiefly on the 

 outer margin of the range, along the spring of the arch, great 

 laccolithic intrusions of igneous material have taken place, which 

 now present either wholly or partly uncovered masses of porphy- 

 ries of several types. Accompanying them are numbers of 

 intruded sheets and dikes. 



The basins cut in shale, the flat-topped plateaux of limestone, 

 the deep gorges cut on the outer flanks of the range and the 



