128 NEW YORK STATE MUSEUM 



and is thus outside the principal areas of Yonkers. The principal 

 opening reveals a bluish gneiss which is much fractured and inter- 

 sected by a pegmatite dike. The latter occupies nearly one-third 

 of the face which measures 60 feet in width. The gneiss strikes 

 north and south and dips 60 ° east. When visited in 191 1, the 

 quarry was equipped with one steam drill and a rock breaker. In 

 recent years the output has been used on the estate of which the 

 quarry is a part for road and foundation work. 



South of the main cut is an opening in a bluish and pink variety 

 of gneiss. The blue is much jointed, while the pink gneiss appears 

 to be very brittle. 



The Beekman quarry has supplied material for several structures 

 in Tarrytown, including churches and other buildings. 



Kensico quarries 



The principal quarry development of recent date in the Yonkers 

 gneiss is that of H. S. Kerbaugh, Inc., the contractor on the new 

 Kensico reservoir which is to form a part of the Catskill water 

 supply system. To increase the capacity of the reservoir, a dam 

 that will be 100 feet higher than the old structure and of corre- 

 spondingly massive proportions is in course of erection at Valhalla 

 at the south end of the reservoir. This structure is to consist of 

 Yonkers gneiss obtained from an area explored to the east of trie 

 ridge, about one-half mile northeast of the dam. 



The geological features of the reservoir site have been presented 

 by Berkey, 1 who also investigated the various quarry materials of 

 the vicinity wii'th the view to their adaptability for use in the work. 

 The Yonkers gneiss is an outlier of the main belt and is exposed 

 on the ridge to the east of the reservoir, while the west side is made 

 up of Manhattan schist, with Inwood limestone in concealed outcrop 

 between the two. 



Berkey mentions several quarries in the vicinity that have not 

 been previously noted. These include the Outlet quarry, 1500 

 feet east of the northern extremity of the old reservoir; the Ferris 

 quarry 1000 feet farther north; and the Dinnan quarry 3000 feet 

 north of the Outlet quarry. All these are in Yonkers gneiss or 

 massive phases of that rock. In addition he mentions the Garden 

 quarry, about midway of the reservoir and 500 feet east of its 

 margin, opened in dioritic gneiss; the Smith quarry, less than 1000 



1 Geology of the New York City (Catskill) Aqueduct. N. Y. State 

 Museum Bui. 146, 191 1, p. 191-200. 



