WARREX AND PALACUE. — QUIXCY PEGMATITES. 147 



magma had solidified. Further differentiation into more or less clearly 

 defined and well characterized zones then took place within this 

 material, possibly by a process of fractional crystallization, althou{,'h we 

 are inclined to believe that the differentiation preceded actual crystal- 

 lization and that each zone crystallized as an individual. This process 

 resulted in still further concentration of the silica, water, fluorine, rare- 

 earths, etc., toward the center of the mass resulting finally in the 

 (juartz centers, and, in the case of the large Fallon ([uarry pipe, of a 

 free space or pocket filled with a watery solution. 



It may be noted here that the graphic-granite zone with its 60 per 

 cent feldspar and 40 per cent quartz seems to depart rather widely from 

 the proportions of these minerals supposed by Vogt and others to be 

 nearly constant and to represent a eutectic mixture. The graphic- 

 granite does not, so far as we can see, correspond either in its mineral 

 composition or in its structural relations to the rest of the pegma- 

 tite, to a eutectic mixture of the minerals of the pegmatite. lu 

 fact, not only in the present case, but in graphic-granites in general, 

 there appear to the writers to be serious, if not fatal, objections to their 

 being regarded as eutectic mixtures. The idea is at present little 

 more than an interesting speculation suggested by a resemblance in the 

 texture to that of known eutectics among metals and a crude approxi- 

 mation in a number of cases to a constancy in chemical composition. 



At some time subsei^uent to the solidification of the pegmatite as a 

 whole, but while there was still liquid in the pocket containing Huorine 

 and some dissolved mineral matter, movements took place in the 

 granite which were sufiicieut to fracture the i)egmatite, fragments of 

 which fell into the pocket. This was followed by the period of resolu- 

 tion and recrystallization already noted as occurring in the pocket and 

 its lining and believed to have been contemporaneous with a similar 

 process in the massive pegmatite and the granite as well. 



It is possible that some portion of the crocidolite formation may have 

 taken place at a later period i)erhaps even subseciuent to the formation 

 of the present system of joint cracks in the granite. As Dale has 

 jxiinted out and others ob.served, the joint cracks are commonly filled 

 with riebeckitic crystallizations, often crocidolitic in character. 



P.\RT II. Special Notes on the Minerals of the Pegmatites. 



Qiotrfz. — Crystallized (juartz is an abundant constituent of the cen- 

 tral pocket of the Fallon pegmatite, individual crystals reaching a length 

 of 30 cm. They are either smoky through included black needles of 

 riebeckite, pale blue from inclusions of crocidolite, or quite colorless. 



