6 



siiicious nature, containing small dark brown or black crystals 

 of amphibole. The base in this case predominates, and is com- 

 pact, having a bright colour. It is often of easy decomposition, 

 and is seen disintegrating at the surface of the earth; at other 

 times, it is exceeding hard and tenacious, giving off sparks with 

 steel, and resembling in appearance some of the Egyptian sy- 

 enites, out of which sphinxes and other pieces of sculpture were 

 formed, specimens of which may be seen in the public sculpture 

 galleries throughout Europe, and in the gallery of the Louvre 

 of Paris: again this rock changes, loosing its porphyritic struc- 

 ture, passing into a compact homogeneous, sonorous, and less 

 tenacious blueish-gray, and even black mineral, thus passing 

 into different traps, greenstones, and Lydian stones. These hills 

 have every appearance of having once been a centre of dislo- 

 cation and elevation, and may have been upheaved after the 

 formation of the transition series. These porphyries and diorites 

 being of Plutonic origin, represent pre-existing rocks thus mo- 

 dified. 



GRAYWACKE SCHIST. 



This rock soon makes its appearance as you descend the 

 Round Top hills, and disappears under the bed of the Conewago 

 creek. It has a dark blue color, and is distinctly, though not 

 finely stratified, and follows the same direction as the phyllades 

 of the transition series of this county, that is, from a few de- 

 grees to the north of north-east, to as many south of south- 

 west. Its schistose structure is not evident in cabinet specimens, 

 but it is distinctly stratified in mass. The graywacke slate of 

 Hunterdon county, New T Jersey, resembles this formation ex- 

 cept in color ; at both localities they are characterized by no- 

 dules of epidote. In York this mineral is more abundant ; it is 

 massive green, and not so mixed with foreign matter as to 

 mask its discriminating characters. The quality of this soil for 

 agricultural process is indifferent, inferior to the limestone land, 

 or that of the red argillacious slate. 



GREYWACKE. 



Immediately 1 after crossing the Conewago creek, the appear- 



