November 27, 1896.] 



SCIENCE. 



801 



ginning with the Jurassic and continuing down 

 to the present. 



M. E. Wadsworth makes a strong plea for the 

 introduction of the elective system in engineer- 

 ing colleges, based upon practical experience in 

 the Michigan Mining School. 



Orotaxis ; A method of geologic correlation : C. 

 R. Keyes. This may be defined as a system- 

 atic arrangement of mountains, or orotaxis, in 

 which the cycles of elevation and degradation, 

 together with the consequent unconformities in 

 the sediments of separate cycles, are made the 

 basis of geological chronology. The method 

 has had its greatest use in pre-Cambrian and 

 other nonfossiliferous series. The author claims 

 that it may serve equally reliable and service- 

 able ends in the correlation of even richly fos- 

 siliferous horizons. 



Human relics in the drift of Ohio: E. W. Clay- 

 POLE. The principal specimen, and the one on 

 which the main argument rests, is a small 

 grooved axe found at a depth of 22 feet in 

 boulder clay. All the collateral evidence, such 

 as the oxydized condition of the axe and the 

 circumstances of the find, points to the genuine 

 antiquity of this relic. 



SOCIETIES AND ACADEMIES. 

 GEOLOGICAL SOCIETY OF WASHINGTON, 



The 51st meeting of the Geological Society, 

 the first of the winter season of 1896, was held 

 in Washington on November 11th, Mr. J. E. 

 Spurr briefly described the reconnaissance of the 

 gold resources of the Yukon region of Alaska, 

 from which he has just returned. The Geologi- 

 cal Survey party in his charge crossed the 

 Chilkoot Pass, about the middle of June, to the 

 headquarters of the Yukon, and proceeded 

 down the river to the chief gold-bearing locali- 

 ties. The principal producing districts, those 

 of Forty-Mile Creek and Birch Creek, were 

 thoroughly explored, as well as other less im- 

 portant localities. The party then continued 

 down the Yukon, examining the younger sedi- 

 mentaries which overlie the gold-bearing for- 

 mation, as far as Nulato. At this point passage 

 was taken by steamer to St. Michael's, and the 

 homeward journey begun. 



One of the principal results of the expedition 

 was the recognition of the gold-bearing rocks 



from which the gold in the river gravels is 

 derived. These gold-bearing rocks constitute a 

 distinct broad belt, running northwest into 

 Alaska from British territory. They are in 

 their lower portions schists and gneisses, with 

 intrusive rocks, and in their upper portion some- 

 what altered sedimentaries. They are all older 

 than Carboniferous, for the Carboniferous and 

 younger rocks overlie them on both sides of the 

 gold-bearing belt. In this belt the gold occurs 

 partly in quartz veins, partly in deposits formed 

 along shear-zones ; in both occurrences it is 

 contained in pyrite, and becomes free on 

 weathering. The quartz veins are distinctly 

 older than the shear-zone deposits, and were 

 formed before the alteration of the enclosing 

 rock to a schist ; they have, therefore, partaken 

 of this shearing, and have been broken and 

 sheared so that they are'typically non-persistent. 

 The deposits along shear-zones are, however, 

 of later date than the shearing, and can be con- 

 tinuously followed. 



The younger beds which overlie the gold- 

 bearing belt consist in part of conglomerates, 

 and some of these conglomerates are fossil 

 placers, which give promise of being productive. 



Mr. S. F. Emmons, of the United States Geo- 

 logical Survey, gave a brief description of the 

 gold deposits of the northern end of the Black 

 Hills of South Dakota. The geological struc- 

 ture of the region is that of a series of steeply 

 upturned Algonkian slates, on the basset edges 

 of which rest nearly horizontal beds of Cam- 

 brian, Silurian and Carboniferous age. All these 

 rocks are abundantly intersected in the mineral- 

 bearing region by dikes and intrusive sheets of 

 various porphyritic rocks, mostly of acid types. 

 Erosion has removed the later rocks and in- 

 cluded porphyry sheets from the valleys, but 

 portions of them remain in the higher ridges 

 and peaks. There are three types of gold de- 

 posits : The Homestake type of deposit, the 

 siliceous gold ores of the Cambrian and the 

 placer deposits. The first occur in sheets often 

 several hundred feet wide along a mineral bear- 

 ing zone, which is mostly controlled by the 

 Homestake Company, and is now worked to a 

 vertical depth of 800 feet. The placer de- 

 posits are partly ancient or fossil placers at the 

 base of the Cambrian (Middle Cambrian, and 



