STRUCTURAL AND STRATIGRAPHIC FEATURES 



OF THE 

 BASAL GNEISSES OF THE HIGHLANDS 1 



BY 



CHARLES P. BERKEY 



General statement 



The lowest and oldest, as well as the most complex in struc- 

 ture and rock variety, of all the formations of the Highlands 

 region of southeastern New York is essentially a series of 

 gneisses. Geographically they extend in a succession of ridges, 

 separated by belts of limestone and schist, with a northeast- 

 southwest trend on the east side of the Hudson river from New 

 York city to the Highlands proper. These separating belts cease 

 in the vicinity of Peekskill and Tompkins Cove, a distance of 

 40 miles from New York. From that locality northward the 

 gneisses constitute almost the whole areal geology, to the 

 northern limits of the Highlands, forming a broad elevated and 

 rugged belt about 20 miles wide whose chief structural features 

 trend northeastward in essential conformity with the ridges of 

 the southern district. Toward the west, below Peekskill, the 

 series is abruptly terminated at the Hudson river. The only 

 other outcrops of these ancient rocks occurring on the west 

 side of this line are at the extreme southern part of the district 

 in Jersey City and Staten Island. Above Peekskill in the High- 

 lands proper the same rocks cross the Hudson and continue 

 southwestward into and through northern New Jersey. On the 

 eastern side this formation and its overlying relatives pass into 

 Connecticut. 



x The observations upon which the present paper is based were made almost wholly in the 

 Tarrytown _ and West Point quadrangles as outlined by the topographic maps. This work, 

 which consisted of careful mapping in these areas, was supplemented by numerous expeditions 

 into the adjacent Harlem, Ramapo, Skunnemunk, Newburgh and Poughkeepsie quadrangles, 

 and has occupied portions of two summers. 



