Invasion to Regional Met amor pJiisni. 17 



feldspathic quartzites. The schists show many segrega- 

 tion seams and lenses of qnartz and feldspar, the quartz 

 holding needles of tourmaline. The boron and fluorine 

 which enter into tourmaline are elements not found in 

 clastic sediments. They are commonly regarded as the 

 evidences of pneumatolysis, but if so, they have the 

 capacity to rise for great distances through metamorphic 

 zones before entering into crystallization as tourmaline. 

 It is well known that tourmaline tends to crystallize, 

 especially in siliceous formations. Apparently, then, the 

 volatile constituents have come as gases from some depth 

 beneath in the Archean complex. That the boron and 

 fluorine have shown a capacity to rise is most clearly 

 shown in a quartzite member within the Stockbridge 

 marble. At Ashley Falls, Massachusetts, the joints in 

 this member show the development of tourmaline crystals 

 in their walls, arranged across the bedding planes. The 

 tourmaline is a replacement mineral lining the cross- 

 cutting joints and developed at the expense of preexist- 

 ing biotite. In the Dalton schist, the development along 

 the foliation planes conceals this kind of evidence of 

 introduction, but the pegmatitic character of the lenses 

 gives support to such a view. 



Of course it is possible to discount the value of this 

 evidence based upon tourmaline, and to cite the existence 

 of fluorite deposits in regions free from any signs of 

 igneous activity.. But it is thought that the evidence 

 given in the first part of this article on the widespread 

 nature of subjacent igneous bodies, tends to support the 

 view that where tourmaline is abundantly present, 

 magmatic emanations were passing through at the time 

 of its formation and supplied the volatile elements neces- 

 sary for its development. 



Another line of evidence is found in extensive infiltra- 

 tions of silica which have developed, in the Stockbridge 

 marble, reefs of malacolite, tremolite, and quartz, over a 

 distance of eight miles between Falls Village, Connect- 

 icut, and Sheffield, Massachusetts. Several varieties and 

 stages of the- action may be noted. Reefs of rugged rocks 

 show that, first, an infiltration of siliceous waters depos- 

 ited quartz in veins. Then an increase in temperature 

 occurred, the waters attacked the lime and magnesia, and 

 coarse-grained tremolite replacements occurred. The 

 reaction did not occur wholly in place, however, since the 

 materials were taken into solution and deposited in veins 



Am. Jour. Sci. — Fifth Series, Vol. I, No. 1. — January, 1921. 

 2 



