May 23, 1902.] 



SCIENCE. 



823 



fault plane is as great as that produced in 

 Appalachian strata generally by the great 

 post-Carboniferous deformation. Thus the 

 shear plane was formed before the principal 

 epoch of Appalachian folding. Whether or 

 not any interval ensued between the two it is 

 difficult to say. Carboniferous rocks are in- 

 volved in the shear plane, so that it was pro- 

 duced at least after the Carboniferous period. 



Mr. J. S. Diller then gave a paper entitled 

 'The Copper Eegion of Northern California.' 

 Mr. Diller stated that the copper region con- 

 tains an extensive series of sedimentary rocks 

 ranging from the Miocene into the Devonian, 

 associated with igneous masses of various 

 ages and kinds which have intercalated or in- 

 truded the sedimentaries. A number of 

 mountain-building epochs are recorded by 

 breaks already recognized in the stratigraphic 

 and faunal sxiccession, and others will doubt- 

 less be discovered in the detailed survey. The 

 general abundance of fossils in the Cretaceous, 

 Jurassic, Triassic, Carboniferous and Devon- 

 ian sediments is such as to render it possible 

 to work oiit the structure in detail. 



The ore deposits of the copper region may 

 he conveniently considered in three groups : 

 Auriferous quartz veins, sulphides in contact 

 zones, and sulphides in shear zones. 



The copper industry has invigorated quartz 

 mining in the region to furnish siliceous ores 

 for smelting. 



The Black Diamond Mine near Bayha 

 shows a number of interesting ore bodies, 

 chiefly pyrrhotite, chalcopyrite and magne- 

 iite associated with diopside, garnet and other 

 minerals on the contact of diabase dikes cut- 

 ting the carboniferous limestones. 



The deposits of the Bully Hill and Iron 

 Mountain districts occur along shear zones 

 mainly within rhyolitic rocks. The ores of the 

 Iron Mountain district are almost wholly 

 pyrite and chalcopyrite, but in the Bully Hill 

 district chalcocite is abundant with much 

 Isarite and sphalerite. 



Mr. Charles Butts presented a paper en- 

 titled 'Recent Structural Work in Western 

 Pennsylvania.' He exhibited maps of the 

 Masontown, Uniontown, Brownsville and 

 'Connellsville quadrangles with structure con- 



tours drawn on the base of the Pittsburg coal 

 up to the western base of Chestnut Eidge, on 

 the top of the Pottsville formation upon the 

 ridge, and explained the methods by whicn 

 the contours were determined. A brief de- 

 scription of structural details was then given. 

 In general the rocks are folded into low 

 ellipsoidal anticlines and shallow canoe- 

 shaped synclines, which often show remark- 

 able minor irregularities of structure and 

 have a decided tendency to offset laterally at 

 short intervals. The structure seems to be 

 intermediate between the steep regular fold- 

 ing of the central Appalachian ridges and the 

 low doming and pitting of the strata farther 

 from the mountains, such as exists in western 

 New York, where it is impossible to detect any 

 linear arrangement of structures whatever. 



A knowledge of the possibilities of such 

 structures can not fail to be of great assist- 

 ance in stratigraphic work in such regions 

 and should diminish its perplexities while in- 

 creasing the reliability of the results. 



The last paper was on the 'Stratigraphy 

 of the Big Horn Mountains,' by N. H. Darton. 



Mr. Darton gave a brief resume of the 

 principal stratigraphic features observed on 

 the eastern flanks of the Big Horn Moun- 

 tains during the summer of 1901. A detailed 

 survey had been made of a portion of the 

 district which is preliminary to more ex- 

 tended investigations. The geologic column 

 comprises all the formations from Cambrian 

 to Laramie excepting perhaps the Devonian 

 and portions of the Silurian. Many fossils 

 were found at various horizons, affording im- 

 portant means for correlation. A limited 

 fauna was discovered in some thin limestones 

 in the top of the Eed beds but its age < has 

 not yet been definitely established. The col- 

 umn was compared with that of the Black 

 Hills which had been studied in previous sea- 

 sons, and a close general similarity is shown 

 including the freshwater Jurassic but not 

 including the Minnekahta (Purple) limestone. 

 Conglomerates found in the Laramie forma- 

 tion indicate a pre-Laramie uplift of the cen- 

 tral portion of the range. 



Alfred H. Brooks, 

 • Secretary. 



