REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1903 193 



DISTRIBUTION OF HUDSON SCHIST AND HARRISON 



DIORITE 



IN THE 



WESTOHE.STER COUNTY AREA OF THE OYSTER BAY 



QUADRANGLE 



BY F. J. H. MERRILL ASSISTED BY H. C. MAGNUS 



In 1900 that portion of the Oyster Bay quadrangle which falls 

 on Long Island was mapped in detail by Prof. J. B. Woodworth 

 and published in State Museum bulletin 48, entitled Pleistocene 

 Geology of Nassau County and Borough of Queens. The north- 

 west corner of this quadrangle falls within the limits of West- 

 chester county and includes portions of the towns of White 

 Plains, Scarsdale, Mamaroneck, Harrison and Rye. During the 

 field season of 1903 Mr Harry C. Magnus has completed the map- 

 ping of the crystalline rocks of this district according to the 

 classification and succession adopted by the author in the New 

 York city folio. As no new points were developed in the course 

 of Mr Magnus's work, the rock descriptions given here are identi- 

 cal with those used in the New York city folio. The map is of 

 interest to students and teachers of the New York city region as 

 supplementing the Harlem sheet published in the folio above 

 mentioned. 



Hudson schist. The schist of the New Y^'ork district receives 

 the name Hudson because it continues northward and connects 

 stratigraphically with the great area of slate and shale along 

 the Hudson river which have been called respectively Hudson 

 slate and Hudson shale. The Hudson schist, Hudson slate and 

 Hudson shale represent different phases of alteration of the 

 same original rock, and together they form the Hudson forma- 

 tion. The Hudson formation continues into New England and 

 is there a schist, which has been called the Berkshire schist. 



The rock is essentially a mixture of biotite and quartz, but 

 frequently contains enough orthoclase to give it the composition 

 of gneiss. The principal accessory mineral is garnet, which 

 occurs in crystals varying from re to ^ of an inch in diameter. 



