A GEOLOGICAL HISTORY. 25 



had the same character as that of 60th Street, 

 mentioned in the description of the Serpentine 

 locality.* There were many boulders of Granite, 

 Gneiss and Greenstone, as large as the two above- 

 mentioned. The place where the young miner- 

 alogists used to roam in search of specimens, is 

 now built upon, and churches and houses cover 

 the spot. 



At 42nd Street, on Murray Hill, at the Distrib- 

 uting Reservoir of the Croton "Water Works, the 

 Diluvium is a tough cement of clay, gravel, and 

 boulders, very hard to dig. In digging through 

 42nd Street, the pickaxe had to be used for every 

 shovelful of this clayey cement' which formed 

 what is called, a hard-pan, of about fourteen or 

 more feet in thickness. At this locality there 

 were more large boulders than at any other, if 

 we except Corlaers' Hook. 



The Diluvium of Manhattanville and Harlem 

 flats, consists of gravel and pebbles, with boul- 

 ders the size of a paving stone, and a few spe- 

 cimens of Kingsbridge marble, but no Serpentine. 

 There is on " the flats," and after you pass the Tun- 

 nel, three or more detached spurs of the Gneiss 



* Boulders of Anthophyllite and Serpentine are strewed all over this 

 island, and Long Island, below the line of 60th Street, 



4 



