1886.] NATURAL SCIENCES OP PHILADELPHIA. 21 



Copper-Bearing Rocks of Lake Superior " (TJ. S. Geol. Survey, 

 vol. V, p. 125), refers to a hornblendic granite containing an 

 augitic core, and the entire mass showing minute flakes of 

 biotite. Mr. Clarence King, in his " Systematic Geology " (U. 

 S. Survey, p. 120), graphically describes the remarkable granitic 

 wall of EI Capitan, in the Yosemite Valley. This presents a 

 vertical face 3200 feet high, dotted with irregular cloud-like 

 masses and lenticular bodies, apparently segregations of the 

 component minerals (brilliant black hornblende, quartz, biotite 

 and orthoclase). This segregation he considers to be the result 

 of mechanical accidents. 



Having thus hastily glanced at observations relating to granitic 

 inclusions in other localities, we are better prepared to under- 

 stand those of the Craftsbury region. In the following consid- 

 erations we will observe, first, the including granite itself; 

 second, the included nodules, their external appearance and 

 internal structure, and the relation of the rock-mass to its 

 inclusions. 



This nodular granite consists of the usual ingredients of a 

 true granite quartz, feldspar and mica. The quartz is the most 

 abundant constituent. It possesses the properties of ordinary 

 quartz as to color, lustre and hardness. The feldspar is the 

 common orthoclase, every light in color even resembling the 

 quartz in this respect. The mica is the black variety (biotite), 

 and is sparingly scattered through the mass. It is in striking 

 contrast with the white components, and gives the rock the 

 appearance of syenite. But no hornblende is present, nor have 

 accessory minerals been observed. These constituents are dis- 

 seminated irregularly throughout the rock-mass, and since they 

 occur in small dimensions, this mass is fine-grained in texture. 

 According to Prof. H. A. Cutting, State Geologist of Vermont, 

 this granite occurs in place like other granites, but south of the 

 beds it consists of numerous large bowlders. 



Professor C. H. Hitchcock refers this granite to the Coos 

 group, which he places directly below the Lower Helderberg 

 division of the Upper Silurian. 



The Incluaions. These are spheroidal or elongated nodules of 

 biotite, from one-half to two inches in diameter, with the long 

 axis sometimes four inches. They ai-e more or less flattened, and 

 frequently consist of only a few plates. Their surface is smooth 



