182 W. H. HOBBS — CHANNELS SURROUNDING MANHATTAN ISLAND 



system. The writer's observations show that many of the most promi- 

 nent joint planes in the rocks of the island have the direction of the 

 cross-fissures — north 60 degrees west.* 



The role of the dolomite in fixing the locations of the present chan- 

 nels would thus appear to have been a subordinate one except in so 

 far as the direction of its boundaries has been determined by fissure 

 planes. 



*Cf. Bull. Geol. Soc Am, vol. 15, 1904, p. 556. 



