ROGERS, GEOLOGY OF THE CORTLANDT SERIES 75 



is then repeated on a smaller scale, with an exceptionally fine grained 

 biotite norite. This is evidently an apophysis of the larger mass project- 

 ing into the schist. On the east, the wall rock is a hornblende pyrox- 

 enite, which seems to be the real country. 



Micaceous Type 



Two of the three larger pits of the McCoy mine and most of the 

 smaller prospects scattered over the hill are of micaceous type, in which 

 a sheared micaceous rock is associated with the ore. The ore from the 

 large pit of the mine, and the chamber connected with it (described 

 above), was the best mined anywhere in the district, except possibly 

 Buckbee's. Small areas of pink and blue corundum emery were found 

 in this pit. In the other pits, it is a lower grade of spinel emery, seldom 

 showing the corundum crystals. 



In the large pit, which is about 80 feet deep, of which depth 30 feet is 

 below water, the sides are not quite vertical, dipping 70°-85° S. This 

 is most apparent at the eastern end, where the wall rock is very mica- 

 ceous, dipping as above and striking IST. 80° E. At times, it strongly 

 resembles Manhattan schist; again, the mica may be all biotite, and the 

 feldspar may diminish until the rock is practically an aggregate of ande- 

 sine, with less orthoclase and a great amount of biotite. Scattered 

 through these minerals is abundant spinel, with varying amounts of 

 corundum. At the west end of the pit, the wall rock is diorite, with 

 strongly pleochroic hornblende, which is in idiomorphic crystals often 

 absorbed and embayed and considerably in excess of the biotite. To the 

 east and south of the mica rock lies a pyroxenite, carrying hornblende 

 and some biotite; and it may also contain sillimanite and garnet. The 

 large veins of ore, if not worked out, are below water level and inacces- 

 sible; but the mica rock carries small veins of spinel emery. Men who 

 had worked this pit stated that the ore was always found in this black 

 mica rock, often associated with garnets; that occasionally white mica 

 was found with it, and that in the ore itself would sometimes be found 

 little bunches of black mica or green mica (clinochlore ?). On the 

 dump, a large amount of the quartzose-streaked emery was found, but it 

 was not observed in place. 



About 50 feet to the east of this pit is the head of a cut extending 300 

 feet east. It is 30 to 60 feet wide, becoming at its head 50 feet deep 

 The wall rock on either side is a typical looking diorite, as in the large 

 pit. Then, starting from the diorite, comes a rock which entirely resem- 

 bles a mica schist (N. 80°-90° E., 75°-90° S.), but which proves in thin 



