3o8 EDSON S. BASTIN 



disappeared. Water gas probably formed the bulk of this cavity 

 filling, though carrying numerous other substances in solution. The 

 abundance of quartz crystals on the walls of these cavities indicates 

 that silica was one of the most abundant of these dissolved substances. 



If the presence of larger amounts of gaseous constituents is respon- 

 sible for the crystallization of the rock with pegmatitic rather than 

 granitic texture, we might reasonably expect greater size or abundance 

 of microscopic fliuidal or gaseous cavities in the pegmatite minerals 

 than in those of the normal granites. With this idea in mind the writer 

 attempted a microscopic measurement of these inclusions in pegma- 

 tites and associated granites from Maine. On account of the uneven 

 distribution of the inclusions in bands traversing the minerals accurate 

 estimates were found to be impracticable and the results were negative 

 or inconclusive. It was found moreover that some of the bands of 

 fluidal cavities in the quartz of pegmatite were formed later than 

 shearing movements which had affected the quartz. The inclusions in 

 the pegmatite were similar in character to those in the normal granites 

 of Maine, and any differences in their size and abundance in the 

 two types of rocks were not sufficient to be noted on casual inspection. 



If the pegmatite magmas are characterized by considerably larger 

 proportions of gaseous constituents than are present in the granite 

 magmas, we might expect notable differences in the contact meta- 

 morphic effects produced by the two types of rocks, since such effects 

 are believed to be produced largely by gaseous and fluid emanations 

 from the cooling igneous masses. Field observations in Maine fail 

 to show that contact metamorphic effects, due to the intrusions of 

 pegmatite, are notably greater than those produced by the granites. 

 The effects produced by both are usually slight and in many instances 

 almost nil. Masses both of pegmatite and granite frequently cut 

 across the foliation of schists without any distortion of the latter, the 

 contacts being of knife-edge sharpness. In other instances pegmatite 

 has produced some softening of the bordering rock. Such effects are 

 confined however to the immediate vicinity of the pegmatite, usually 

 to a zone a few inches in width, and are the exception rather than the 

 rule, most pegmatite contacts being exceedingly sharp and free from 

 all evidence of softening. Absorption (except in a few doubtful 

 instances) appears to be wholly absent, the contacts, even in the cases 



