RECORDS 75 



Professor Hobbs finds that no correspondence can be estab- 

 lished between the directions of the belts of limestone or dolo- 

 mite and of the New York water front, except within the stretch 

 from Kingsbridge to Macomb's dam bridge. Along this line 

 too the observed facts point to the occurrence of a narrow strip 

 of limestone dropped down between vertical faults. The sec- 

 tions of the Harlem River which are furnished by the bridges 

 across it show clearly that it is not a simple erosion valley re- 

 sulting from cutting by the stream. The bed of the stream is 

 marked by sudden changes of level, and the Harlem seems to 

 have chosen its course quite independently of ridges of the 

 harder gneiss. Under the East River limestone has been found 

 at but tw^o localities — under the channel east of Blackwell's 

 Island, and in one of the drill holes underneath the Manhattan 

 pier of the East River bridge No. 3. The limestone east of 

 Blackwell's Island is enclosed between parallel fault walls, and 

 appear to have been dropped down along them. The numerous 

 occurrences, however, of gneiss, and gneiss only along, in and 

 under the East River leave little doubt that the main portion of 

 the bed is composed of this rock. 



Regarding the bedrock beneath the North River, compara- 

 tively 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 evidence derived from the borings along 

 the route of the proposed tunnel 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 joining and displacement. Man- 

 hattan Island borders directly upon the Newark 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, especially of the northern half of it, and its topo- 



