ELISHA MITCHELL SCIENTIFIC SOCIETY. 81 



nately broken by careless handling in the mine. Although no 

 large quartz crystals have been obtained from these mines, large 

 masses of crystallized quartz (generally the darker colored sorts) 

 are constantly met with. The accompanying small red garnets 

 are generally sprinkled through the quartz, and not through the 

 mica or feldspar. 



FORMATION* OF THE MICA VEIN-. 



The free play which the crystallizing forces enjoyed between 

 the enclosing walls of the vein is one of the remarkable phe- 

 nomena to be observed in these mica mines. Now here else can 

 this be seen on such a scale. The development of a single min- 

 eral in a vein is not uncommon, but the wholesale crystallization 

 of all the chief constituents of a vein is very infrequent. It is 

 worthy of notice here that in a mica vein these constituents are 

 highly siliceous. Taking the percentage of silica in the quartz 

 as the standard, we have the percentages of silica as follows : 



Per cent. 



Quartz 100 



Feldspar (orthoclase) 64.72 



Mica imuscovite) 45.75 to 51.80 



Garnet 35.00 to 52.11 



Garnet is here included because, although it does not occur in 

 large crystals, it is nearly always present, and in considerable 

 quantities, sprinkled in the quartz. This, so to speak, excessive 

 extension of the crystals would seem to imply that they met with 

 but little resistance, or that the resistance was easily overcome. 

 W. C. Kerr was of the opinion* that many of the irregularities 

 of these veins, in form, size and position, were due to the efforts 

 of the vein matter to intrude itself. These irregularities, how- 

 ever, seem to me to be chiefly due not to this cause but to the 

 original Assuring forces. It may indeed be true that in the at- 

 tempt to crystallize the vein matter caused some irregularities in 

 the shape and size of the fissure, but this is a force different in 



'Engineering and Mining Journal, Vol. XXXII, No. 13, p. 211. 



