74 RECORDS 



Summary of Papers. 



Wallace Goold Levison exhibited to the Section four speci- 

 mens of gneiss obtained from the bedrock in certain deep ex- 

 cavations at the southern end of Manhattan Island. One of 

 these was collected July 20, 1902, from a depth of fifty feet 

 below the surface at the corner ot Broad and Exchange Streets ; 

 the second was collected in the excavations at 40 Exchange 

 Place, forty-five feet below the surface, on July 25 ; two 

 others were collected at 43-49 Exchange Place, forty-five feet 

 below the surface, on July 25. Mr. Levison also showed 

 several specimens of serpentine from boulders found in excava- 

 tions for the Stock Exchange building on Broad Street, be- 

 tween forty and sixty feet below the surface, on June 19. 



In the absence of the author, the paper by Professor William 

 H. Hobbs was read in somewhat condensed form by the Secre- 

 tary of the Section. The paper was accompanied by a wealth 

 of detailed observations too extensive for reproduction, but a 

 summary of his conclusions is as follows : 



In his introduction the author called attention to the unusual 

 opportunities now offered for studying the geology of Manhat- 

 tan Island through the numerous great engineering works in 

 progress. The waterways surrounding the island are deep 

 caiions, with a depth of nearly two hundred feet in the East 

 River and three hundred feet or more in the North River, now 

 partly filled with drift deposits, the amount depending upon the 

 velocity of the tidal currents. 



In 1865 Stevens advanced the theory that the river channels 

 followed lines of faults (" longitudinal and transverse fractures "). 

 Newberry regarded the East River as the lowest reach of the 

 Housatonic River before it discharged its waters into the Hud- 

 son, which was then the outlet of the Lorentian series of lakes, 

 and he considered the Harlem River with Spuyten Duyvil 

 Creek a smaller tributary of the Hudson. Dana believed that 

 the relatively easy solution of certain beds of limestone deter- 

 mined the position of the river channels. This view of Dana's 

 has been supported by Kemp and F. J. H. Merrill, while 

 Gratacap rejects the theory advanced by Stevens. 



