338 THE VERMILION IRON-BEARING DISTRICT. 



secondary minerals, wliicli in some cases, where the rocks are completely 

 recrystallized, are the sole constituents: Chlorite, epidote, sericite, actinolite, 

 massive dark-brown and green hornblende, quartz, calcite, and pyrite. The 

 material between the grains in the coarser sediments is made up of sericite, 

 chlorite, epidote, quartz, and feldspa,r, and this is believed to have been 

 produced, as stated above, from the fine detrital material originally lying 

 between these grains. In the very fine-grained rocks, where the crystalline 

 character of this interstitial material is recognizable, but where the indivi- 

 duals of it could not be determined, they are presumed to be the same as 

 those just enumerated. These materials are present in varying proportion, 

 which produces, of course, the differences in color and chemical composition 

 of the rocks; for instance, some of the lighter colored rocks — the light 

 cherts, for example — are composed essentially of quartz in very fine 

 crystalline particles. Other rocks are made up essentially of quartz and 

 feldspar in waterworn grains, with some of the fine interstitial material 

 between. Others again contain, in addition to the quartz and feldspar, a 

 large quantity of pyroxene and of hornblende, and are very dark, usually 

 dark green, and apparently fairly basic in character. A few rocks contain 

 calcite in considerable amount, but never in sufficient amount to be called 

 limestone. Moreover, this calcite is believed to be of secondary origin, 

 derived from the alteration of the minerals forming the rocks or else 

 introduced from other sources by infiltration. 



The general alteration which the minei'als of these rocks have already 

 undergone has been referred to. The addition of new minerals is cleai'ly 

 shown in the case of the hornblende of some specimens. In these we find 

 the fragments of dark-brownish hornblende surrounded by recently added 

 massive light-greenish hornblende. The hornblende grains in some cases 

 have been increased to two and even three times their original length." 



The changes which have taken place in some of the rocks show very 

 well how, by somewhat further changes, banded crystalline schists might 

 be produced which would offer no clue but the banding to a determination 

 of the kinds of rocks from which they were derived. Thus some of the 

 fine-grained sediments, rich in hornblende, have nearly all of the pieces 

 of hornblende, very commonly cleavage pieces, arranged with their long 



a Enlargements of hornblende fragments, by C. R. Van Hise: Am. Jour. Sci. , 3d series, Vol. XXX, 

 1885, pp. 231-235. 



