Geology of IIu(ho)i County, New Jersey. 31 



Long Dock, Jersey City, and which appears at the surface in the 

 hills on Staten Island ; some of the deep wells in Jersey City, or 

 at Tinibech and Betz's brewery on Ninth Street, near Grove 

 Street, — which at a depth of between 700 and 800 feet penetrated 

 a light-colored rock, that yielded a supply of water strongly im- 

 pregnated with magnesia, — indicate that they penetrated ser- 

 pentine or some closely associated rock. 



The serpentine outcropping on Manhattan Island, at the foot 

 of GOtli Street, near the Hudson, is quite different in its charac- 

 teristic features from the serpentine appearing at Hoboken ; it 

 is compact, very dark-green or nearly black in color, and is 

 sometimes mingled with calcite, forming an opMcalcite that is 

 strikingly similar to the Canadian serpentine in which Eozoon 

 is found ; other portions of this serpentine are spangled with 

 flakes of talc, or shot through Avith bladed crystals of tremolite ; 

 and associated with it occurs anthophyllite. 



At a number of localities, both northward and southward, in 

 the New York belt of Arch^an rocks, beds of dark-green ser- 

 pentine are found, bearing sometimes a close resemblance to 

 that occurring at Hoboken ; v/hile the serpentine occurring in 

 the crystalline rocks of the New Jersey highlands, and in the 

 corresponding formation to the eastward, in New England, is 

 commonly the light-colored or precious variety. 



At Hoboken, the serpentine appears to rest upon the gneiss 

 rocks which outcrop farther south ; it is probably but a portion 

 of the same series, however, and corresponds in position with 

 the serpentine found so abundantly in the Archaean rocks of 

 other regions. This rock is essentially a silicate of magnesia, 

 and contains also chrome iron scattered through it in small 

 specks and grains ; from the fissures in the rock the magnesian 

 minerals, marmolite, irucite, nemalite and magnesite may be 

 obtained. 



As stated by Mr. AVard,* the serpentine is granular and 

 porous in texture ; absorbs surface-water promptly, thereby 

 greatly promoting natural drainage ; transmits heat very slowly 

 but retains it. tenaciously, forming a highly salubrious sub- 

 stratum. 



* Memorandum on the Soil, Contour and Drainage of Hudson County. By L. B. Ward, C. E. 

 Rep of County Board of Health, 1877, p. 8. 



