146 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



of magnesian rocks which covers the emery bed seems to have been the 

 source of the magnesia in this mineral. The less altered ferruginous 

 limestone below was changed into the epidotic amphibolite. 



While thus magnetite, emery, and corundophilite form the first genera- 

 tion of minerals of the bed, the latter mineral continued to be formed or 

 reformed in the abundant fissures produced by the continued intestinal 

 movements of the mass, cementing the breccias and forming thick cross- 

 veins with a fine-grained chloritic mass, at times closely resembling an 

 aphanitic hornblende rock, and in this form abundantly associated with 

 tourmalines (always in regular six-sided prisms), with epidote and pyrite. 

 In a third and more quiet stadium the corundophilite formed incrusting 

 layers upon the free surfaces of fissures, made up often of congeries of 

 broad, vertical plates terminated above in well-defined faces, and associated 

 with rutile, brookite, menaccanite, calcite, diaspore, margarite, and epidote. 



This stadium is closely parallel to the customary secondary fissure 

 deposits of the associated rocks, especially the hornblende-schists, which 

 consist usually of prochlorite, menaccanite, rutile, calcite, and epidote, and 

 is peculiar only in the substitution of corundophilite for the ordinary 

 chloi-ite and in the presence of the satellites of emer}', diaspore, and 

 margarite. 



The foui-th and final stadium in the development of the minerals of 

 the vein seems to be quite distinct from and later than the preceding and 

 to indicate the presence of steam or heated and gradually cooling waters in a 

 new set of fissures which cut across the older diaspore-margarite veins, and 

 thus prove the later appearance of the new series of minerals. The suc- 

 cession^specular iron, aragonite, calcite — clearly indicates at first steam or 

 hot water for the formation of the first and second, and a transition to cooler 

 water for the formation of the last. The sudden appearance of the calcic 

 carbonate in considerable abundance is also interesting. Calcium is Avholly 

 wanting in the first and second stadia defined above. A trace of calcite 

 and epidote in small amount, together with margarite, represents altogether 

 but a small quantity of this element in the third stadium, while here the 

 carbonate makes up ths greater portion of the new series and may have 

 been introduced from without, possibly set free by decomposition of tlie 

 hornblende in its change into serpentine. 



