Ries — Geology of Orange County. 



453 



The Clove mine is about a mile and one-half south of Monroe. The 

 workings are full of water and Little of their relations can be made out. 

 According to Mather* the ore occurs in several parallel veins. This may be 

 due to faulting. The walls of the mine are a hornblendic gneiss which, at 

 times, becomes very schistose, and the ore has much hornblende and a 

 silvery mica mixed with it. Pyrite is occasionally present. The nearest 

 gneiss exposure to the east of the mine is very cpiartzose and does not 

 represent the normal rock. On the west are several outcrops of a feldspathic 

 granitic gneiss. The ore-body is evidently cut by a dike, judging from the 

 numerous angular fragments of it which were found on the dump heap. Tin- 

 dike is a tine-grained black rock, cut by numerous thread-like streaks of 

 pyrrhotite. 



Woodbury Township. The gneissic rocks cover about five-eighths of 

 the area of the township. The line of faulting which has given rise to the 

 Ramapo valley south of Turners, passes northward along the base of the 

 gneiss ridge east of Turners and Central Valley, and then along the narrow 

 valley east of Pine hill, at whose north end the fault-line probably passes into 

 the Highlands. Up to the point east of the north end of Pine hill, the fault 

 line is between the gneiss and the Cambrian limestone. A contact of the two 

 is well exposed in the limestone quarry a mile and one-half northeast of 

 Arden. A tine fault cliff is also to be seen on the western side of the valley 

 just north of Arden. The grey gneiss, which is faulted against the limestone 

 in the upper portion of the limestone quarry, dips steeply to the east. It is 

 a fine-grained granular mixture of quartz and plagioclase with a little 

 orthoclase and biotite. The rock shows the effect of crushing, and the larger 

 grains are embedded in a crushed matrix of the same minerals cemented 

 with decomposed biotite and limonite. 



About one mile below the quarry, a road leaves the main one of the 

 valley and turns to the east through a shallow ascending valley to the other 

 side of the ridge where it turns to the north. Just beyond a church and 

 where the road turns, a granular gneiss appeal's, which is cut by uumerou> 

 granite veins. It strikes N. 20° E., and dips 70° S. E. (284). The gneiss in 

 section is seen to consist of quartz, plagioclase and some orthoclase. The 

 quartz grains often show a zonal structure, and the twin lamellae of the 

 plagioclase are not unfrequently bent, The rock is considerably decomposed. 

 This gneiss passes into a very hornblendic facies. 



* Geology of New York, 1842, p. 571. 



