132 THE CRYSTAL FALLS IRON-EEAPjyG DISTRICT. 



The matrix, representing tlie most altered phase, is a granular aggre- 

 fj-ate of calcite, in which one may here and there discern small clear limpid 

 grains of secondary quartz and feldspar (?) and flakes of chlorite. The 

 calcite includes in considerable quantity the globular bodies mentioned. 

 These are found also in the spaces between the calcite grains, as though 

 pushed away from the grains as they crystallized. 



Some of the calcite in the first stages of the alteration of the rock may 

 have been derived from a basic feldspar It is clear, however, that the 

 great mass can not owe its origin to this process, but must be the result of 

 infiltration. The calcite grains derived from, and lying in, the feldspar 

 acted as nuclei, around which the infiltrated calcite was gradually col- 

 lected, producing pseudomorphs after the feldspar laths. Quite recently 

 Dr. W. S. Bayley^ has noted in the Clarksburg submarine volcanic forma- 

 tion of the Marquette district, Michigan, the occurrence of tuffs, in which 

 calcite has been introduced in such quantity that they may almost be called 

 limestones. 



In another case in which the alteration of the ellipsoid (PI. XI) appar- 

 ently proceeded along the lines of shearing, and produced the kind of 

 aggregates of chlorite, including crystals and aggregates of epidote- 

 zoisite, which were described (p. 117) as the usual matrix of such ellipsoids, 

 one can see in thin section the calcite entering the chlorite aggregate along 

 minute fissure lines. The calcite literally eats its way into the chlorite, 

 and produces by an interchange of elements a mass of calcite (magnesian I) 

 and epidote, besides including epidote which originally occurred scattered 

 through the chlorite aggregate. 



The carbonation of the original basalt or of the secondary chlorite 

 mass results in producing a mass of carbonate which has associated with 

 it some secondary quartz, chlorite, and epidote. This carbonate mass may 

 be almost massive or it may be decidedly schistose. When schistose, the 

 grains of calcite and quartz have a uniform elongation, and the schistosity 

 is materially enhanced by flakes of chlorite, which are not uncommonly 

 found in thin streamers or thick masses in the carbonate aggregate, at times 

 in sufficient quantity to give it macroscopically a decided green tinge. 



I have used the term "carbonate," although having described in detail 

 above the calcification of the basalt, for the reason that at times, and for no 



I Mon. U. S. Geol Survey, Vol. XXVIII, p. 473. 



