906 



SCIENCE. 



[N. S. Vol. XVI. No. 414. 



occurrences, however, of gneiss and gneiss only 

 along, ill and under the East Kiver leaves little 

 doubt that the main portion of the bed is 

 composed of this rock. 



Regarding the bed-rock beneath the North 

 River, comparatively little is known, but the 

 origin of its channel is sufficiently accounted 

 for by its position along the contact of the 

 Newark system with the crystallines. This 

 contact seems surely to be a fault-border on 

 account of its markedly rectilinear extension, 

 the great scarp of basalt, the much inferior 

 position of the newer terranes, and the evi- 

 dence derived from the boring along the route 

 of the proposed tunnels of the Pennsylvania, 

 New York and Long Island railroad company. 



The author holds that the directions of the 

 channels of Spuyten Duyvil Creek and Harlem 

 and East Rivers have been determined largely 

 by lines of jointing and displacement. Man- 

 hattan Island borders directly upon the New- 

 ark area, in which the existence of a network 

 of faults has been established by the work of 

 several observers, and the network probably 

 extends beyond the limits of the area. The 

 striking rectilinear outlines of the island, es- 

 pecially of the northern half of it, and its 

 topographic development are favorable to the 

 view that it represents an orographic block 

 left standing between down-thrown strips of 

 the crust. The rectilinear gorge of the upper 

 Harlem between Washington Heights and 

 Fordham Heights is continued, so far as its 

 western wall is concerned, some two and a 

 half miles south of the river. It is parallel to 

 the direction of the scarp of the Palisades, 

 and of the Hudson. Besides the cross frac- 

 tures indicated by the different parts of the 

 Harlem River, which were pointed out by 

 Stevens, several other cross fractures on and 

 about Manhattan Island were pointed oiit by 

 the same author. Dana also considered that 

 the Manhattanville cross valley was formed by 

 a cross fracture. A considerable number of 

 faults has been definitely established. Their 

 directions correspond in general to the ele- 

 ments in the course of the river channels. 

 The exceptions to this rule are the fissures in 

 the East River east and west of BlackwelLi 

 Island. 



The author went on to cite a number of 

 faults which have been disclosed by numerous 

 borings and tunnels, and, in closing, called 

 attention to the fact that the buried rock-sur- 

 face in the lower part of the city (south of 

 Twenty-third Street), as well as that below the 

 area of the Harlem flats (north of One Hun- 

 dred and Tenth Street and east of Eighth 

 Avenue), is characterized by the most abrupt 

 changes of level. In his opinion the area of 

 these portions of the island represents oro- 

 graphic blocks depressed by faults, reefs of 

 gneiss and limestone rising along the Harlem 

 area, while reefs of gneiss alone characterize 

 the southern district. 



Professor Hobbs' paper was discussed briefly 

 by Professors Kemp, Dodge and Stevenson, 

 and it was evident that the author's theory 

 would not be accepted without considerable 

 further investigation. 



At the outset of his paper on Bingham 

 Canon, Professor Kemp stated that the article 

 was not a formal one for publication, and that 

 he did not wish to forestall in any degree the 

 forthcoming Bingham folio by Mr. Boutwell, 

 of the United States Geological Survey. He 

 then described the geological formations in the 

 vicinity of large mines. These formations 

 embraced the great section of quartzite with 

 smaller exposure of limestone, and with in- 

 truded masses of eruptive rocks which range 

 from pronounced porphyries to granites. At 

 least three kinds of eruptives can be distin- 

 guished. The author described in outline the 

 faults and geological relations of the ores, and 

 stated that the ores especially favored the 

 contact of the eruptive rocks with the quartz- 

 ites. The evidences of contact metamorphism 

 between the porphyries and the limestones 

 were commented upon. The ores in the great 

 porphyry dike on the claims of Colonel Wall 

 were described, and were stated to be sec- 

 ondary in their origin — that is, they were 

 probably introduced in solution into a mass 

 of crushed eruptive rock. The data for the 

 paper were gathered in connection with the 

 field instruction given to a class of students 

 the past summer. The paper was illustrated 

 by means of lantern slides, maps and speci- 



