MAN HA TTAN ISLAND ROCKS 7 



schists, the general trend ("strike") of which is N.N.E.-S.S.W. 

 These rocks can be studied in almost every excavation for build- 

 ing purposes, and there are numerous excellent exposures of 

 them, which fortunately will never be covered, in Central, 

 Riverside and Morningside Parks and along the Speedway and 



MICACEOUS GNEISS 



A block of Fordham Gneiss (Archaean) from the east end of Washington 

 Bridge, N. Y. Closely resembles the gneiss of Manhattan Island. Specimen 

 is 20 inches across. 



Lafayette Boulevard. The area of serpentine is very small and 

 is now inaccessible on account of buildings. It is at Tenth Ave- 

 nue and West Fifty-eighth Street. The magnesian limestone, or 

 dolomite, occurs in zones in Harlem, where it is now almost 

 covered with buildings, and in the Kingsbridge section of the 

 island, where a good exposure may be seen along the Spuyten 

 Duyvil ship-canal. 



The exact distribution of these rocks can best be learned 

 from a study of the geological map of New York City and vicinity 



