242 PROCEEDINGS OF THE ACADEMY OP [1884. 



Granite. — This rock, as known in the State, is divided into two 

 clashes: (1) that which forms intrusive beds, being a coarsely 

 crystalline orthoclase granite, and (2) that which is nothing more 

 than a highly metamorphosed granitic gneiss, or mica schist, it 

 being a very compact, fine-grained rock. The former variety may 

 be described as an intimate mixture of flesh-colored orthoclase, 

 quartz and muscovite mica, with which are often associated albite 

 and biotite. It occurs as veins, usually bedded, which vary in 

 width from 6 inches to 25 feet, and which, though often continuing 

 in length for several miles, are known to pinch out entirely. 

 The great difference in lithological character between the enclosing 

 rocks and these beds would imply that the latter are veins of 

 plastic injection from aqueo-igneous fusion. That the intrusion 

 of the semi-molten magma was subsequent to the uplifting and 

 crystallizing of the enclosing rocks, is proven by the fact that the 

 latter have, in the vicinity of such veins, suffered considerable 

 disturbance and undue metamorphism at the planes of contact 

 with the intruded mass. The granite is often so highly feld- 

 spathic as to be worked exclusively for this mineral, and when 

 the upper portions of such veins are greatly decomposed, dig- 

 gings have in a few cases been made for kaolin. 



One of the most noticeable of these veins of coarse granite is 

 found to cut across the road leading up the Brandywine, about 

 one and a half miles from the head of the State. A large quarry 

 has been opened in this vicinity, where the rock has been worked 

 for feldspar. The vein is not less than 20 feet wide, on the one 

 side of which is a highly metamorphosed mica schist, and on the 

 other hornblendic gneiss. The rock is a mixture of red ortho- 

 clase, albite, blue quartz, and muscovite, the crystals being some- 

 times so large that perfect specimens of feldspar several i inches 

 square, can be obtained. Large hexagonal plates of mica, many 

 of them 6 inches across, are also found in abundance. The same 

 feldspar is worked three miles to the northeast, probably from the 

 same vein, as near as could be determined ; while in the other 

 direction the intrusive mass seems to lose itself. 



Another equally wide vein cuts across the Newark and Avon- 

 dale R. R., at Tweed's mill, two miles north of Newark. A 

 faulting plane cuts through this intrusive bed, possibly due to its 

 disturbing action. 



The same rock is found to continue two miles and a half to the 



