82 JOURNAL OF THE 



kind and degree from the intrusive force referred to. In the 

 work of intrusion the temperature of the intruding mass would 

 have been lowered. As this process went on, and more and 

 more work was accomplished, the temperature would tend more 

 and more towards the point at which the crystallization would 

 set in, unless a new source of heat was at hand and available. 

 The amount of heat given out by the solidifying vein matter 

 would of course be the same as was absorbed by it in first assum- 

 ing the liquid state. Whether the amount of heat equivalent to 

 the effect of intrusion- would be less than equal to or greater than 

 the amount thus set free is a question upon which I do not now 

 propose to enter. The subterranean forces causing the ascension 

 of the vein matter in a liquid or semi-liquid condition could have 

 forced it into the various ramifications of the fissure and have 

 thus left it to follow its own crystallizing tendencies. That there 

 was little or no hindrance to it in passing to the solid state is 

 shown by the size of the resulting crystals. The great and ex- 

 tended irregularities iu these veins I would therefore attribute 

 primarily to the original Assuring forces, the small and more 

 local ones to local causes, among which may be included local 

 intrusion and local crystallization. 



At whatever point within the fissure we consider the vein 

 matter, whether before or after crystallization, it will appear as 

 completely filling it. A "horse" within a mica vein is seldom 

 met with. There is one at the Sink Hole mine. Here the in- 

 closing rock is mica schist, and the following succession of sub- 

 stances has been observed from wall to wall:* 1st, mica; 2d, a 

 "horse' 7 of mica schist; 3d, smoky quartz; 4th, mica; 5th, 

 smoky quartz; 6th, a "horse" of mica schist; 7th, mica. 



The deposit of mica between the "horse" and the wall is nar- 

 row, but yields good mica. The greater part of the mica in the 

 vein crystallized first, and probably in this process tore off a piece 

 of the wall, the space left by it being subsequently filled with 

 mica. The pieces torn off are somewhat more decomposed than 

 the original walling. 



*W. C. Kerr, ut supra. 



