340 Geology of Long Is i and. 



drift, we will now consider in detail the strata which underlie it. 

 The crystalline rocks outcrop along- the shore at Hellgate and 

 over a limited area in the vicinity of Astoria. They consist of 

 finely laminated gneiss and schists, tilted at a high angle, and 

 belong to the same formation as the rocks of Manhattan 

 Island. I am informed by Mr. Elias Lewis, Jr., that in 

 boring an artesian well in Calvary Cemetery, near Brooklyn, a 

 bed of gneiss was encountered at a depth of 182 feet. Further 

 than this, we know nothing of the extent of the crystalline rocks 

 on Long Island. The section obtained in the boring mentioned 

 was as follows : 



Surface loam and drift, 



139 feet, 



Greenish earth, - 



- 39 " 



White clay with red streaks, 



4 " 



Gneiss, 



- 400 " 



Total, - - 582 feet. 



The greenish earth referred to, lost its color on being treated 

 with hydrochloric acid, and the white residue examined under 

 the microscope appeared to consist of minute fragments of kao- 

 linized feldspar, with occasional grains of quartz sand. The 

 acid solution gave a strong reaction for iron, indicating a proba- 

 ble admixture of glauconite with the material. It is stated in 

 Cozzens' Geol. Hist, of N. Y. Island, that a shell of Exogyra 

 costata, with green-sand adhering, was found between Brooklyn 

 and Flatlands, at a depth of 60 feet. This locality is about five 

 miles south of the well just mentioned, and would indicate the 

 presence of Cretaceous strata near Brooklyn. 



The following data, also furnished by Mr. Lewis, of a well dug 

 by the Nassau Gas Light Co., in Williamsburg, will give an idea 

 of the formation at that locality : 



Surface loam, 



- 3 feet. 



Quick-sand (so called), 



2 " 



Boulder clay, somewhat sandy, 



- 7<) " 



Blue clay with pebbles. 



27 " 



Oyster shells, 



6 inches, 



Total, - 102 feet 6 inches. 



