138 NEW YORK STATE MUSEUM 



which is in the scales arranged parallel to the foliation makes it 

 readily cleavable and is a source of weakness if proper care is not 

 used in laying the stone. It should not be placed, of course, on 

 edge, as the effects of water and frost are greatly accentuated 

 if the foliation is thus exposed. 



There are no permanent quarries in the Manhattan schist. Most 

 use of this stone has been made in foundation and retaining walls 

 on Manhattan island and much of the material has been taken from 

 excavations on building sites. The local operations, therefore, do 

 not call for special mention. 



GRANITE NEAR RAMAPO, ROCKLAND COUNTY 



The belt of Precambric gneisses which enters southwestern Rock- 

 land county from New Jersey, forming the massive ridges of the 

 Ramapo mountains, contains several quarries around Sufifern and 

 Ramapo which have supplied building stone for local uses and to 

 some extent for shipment. The gneisses are pink or gray and 

 carry hornblende or biotite as the iron-magnesia mineral. In gen- 

 eral composition they resemble granite, being composed mainly of 

 acid feldspar and quartz. They range from foliate, thinly bedded 

 types to heavily jointed massive examples. The latter, of course, 

 are better adapted for all constructional work, in which they take 

 the place of true granite. They are intersected by vertical joints 

 of which there is usually a system running nearly north-south and 

 a second at about right angles. 



The quarry sites are situated along the Erie Railroad between 

 Suffern and Ramapo. One of the principal openings, but idle 

 for many years, lies on the ridge south of Ramapo and west of 

 the railroad tracks. The rock is a hornblende gneiss of massive 

 character, reddish in color. Smock mentions the quarry as having 

 furnished building and monumental stone, as well as material for 

 many of the Erie Railroad bridges. 



A quarry near Hillburn was worked by Rice Brothers up to the 

 year 1904. The output consisted of building, monumental and 

 rough stone. 



GRANITE AND GNEISS IN ORANGE COUNTY 



Several granite intrusions are found in the southwestern part 

 of Orange county, near the New Jersey state line. Two of these 

 constitute rather large bosses that rise into the conspicuous twin 

 peaks Mounts Adam and Eve, at the edge of the " Drowned Lands " 



