THE MAXHATTAX SCHISTS 423 



tings and parks, and their varied character and easy access make this 

 island, at present, a specially interesting field for study of this question. 



Manhattan Series of Schists 



Through the investigations of S. Akerly (1820), L. D. Gale (1839), 

 W. W. Mather (1843). I. Cozzens (1843), R. P. Stevens (1865), J. D. Dana 

 (1880-1881), J. F. Kemp (1887), L. P. Gratacap (1887), F. J. H. Merrill 

 (1880-1896), D. H. Newland (1901), etcetera, the schists which make up 

 Manhattan island and Westchester county, New York, which adjoins it 

 on the north, have been assigned to the following four classes, stated 

 from above downward : 



Micaceous gneisses, fine grained, gray, biotitic. in large part pegmatitic 

 ("Manhattan schist" or " Hudson schist'' of Merrill), make up the 

 mass of the island. In them occur thin intercalations, characteristic 

 but in small amount, of biotite-muscovite schists of high luster, rich in 

 quartz, with a little feldspar, cyanite,sillimanite, fibrolite, garnet, apatite, 

 and staurolite, : also amphibole rocks and serpentine. The thickness 

 of the stratum has been estimated to exceed 1.000 feet. 



Dolomitic granular limestone (" Inwood limestone '' or " Stockbridge 

 dolomite" of Merrill), rich in phlogopite and tremolite, with diopside, 

 black mica, black and brown tourmaline, rutile, serpentine, etcetera. Its 

 individual beds are thin, in one case 150 feet, alternating with micaceous 

 gneiss. Thickness estimated from 600 to 800 feet. 



White quartzite, massive to granular (•' Lowerre " or " Poughquag " 

 quartzite of Merrill) ; entirely wanting on the island, wdiile in the 

 vicinit}^ it rarely exceeds from 12 inches to 2 feet in thickness, though 

 infrequently it reaches 5 to 10 feet. 



Laminated quartzitic gneiss, light gra}^ biotitic (" Fordham gneiss " 

 of Merrill), often pegmatitic, which consists of granular quartz (about 

 two-thirds, by Dana's estimate), with micas, feldspars, apatite, zircon, 

 titanite, and occasionally magnetite and garnet. Thin intercalations 

 occur of lenses of mica schist, micaceous gneiss, white quartzite, pegma- 

 tite, and black hornblende schist. In vicinity to the overlying limestone 

 it has been found calciferous. Thickness estimated as at least 200 feet. 



Underlying the above series a red gneissoid granite (" Yonkers gneiss " 

 of Merrill) makes its appearance at many points. It is made up of 

 quartz, reddish orthoclase, a little plagioclase and biotite. Sometimes this 

 passes into fine granular or micaceous aplite, with muscovite or hydro- 

 mica, garnet, and tourmaline. It rises as intrusive bosses into the 

 quartzitic gneiss at Yonkers and at Union Corners, Westchester county, 

 New York, into the micaceous gneiss of Manhattan island near West 



