118 THE PENOKEE IRON-BEAEINO SEKIES. 



approxiiuatelv <it uuit'onn size in eafli section, although varying- widely iu 

 different sections ; in general they have roundish or <>\al forms. The parti- 

 cles of the two minerals fit each other very closely, Init do not intricately 

 interlock. The efltect of this even grained background composed of round- 

 ish particles is to suggest a fragmental origin, but nowhere is there any 

 conclusive evidence that any of the material is of fragmental character. If 

 the grains represent fragments they could not have thus ]>erfecth' fitted each 

 other as originally deposited, and nowhere is there any proof of enlarge- 

 ment in either the cpiartz or feldspars, and there is no space between them 

 for a finegrained interstitial material; so this granular structure can not be 

 taken as proof of fragmental origin. 



The felds|)ar is very largely of the species orthoclase, although micro- 

 cline aiid plagioclase are often aljundantly present. It has usualh' largely 

 altered, the resultant products being kaolin, sericite, chlorite, epidote, and. 

 at times biotite and hornblende. '^Fliis alteration is sometimes ceiiainl}', 

 and jjrobably often, attended with the simi;ltaneous se])aration of cpiartz. 

 This decomposition in the cases when it has extended far enough results iu 

 j)i-oducIng in the place of a feldspar a complex interlocking mass of iinely 

 crystalhne material. In a i'ew cases in which the gneiss was originally 

 strongly feldspathic the alterations liave caused it to closel)- resemble some 

 of the feldspathic gravwackes of the Upper slate member of tlie Penokee 

 series (chapter vi). As mentioned in the case of a similar ficcurrence in 

 the Western granite there is, however, the great difference that no evidence 

 can here be found tluit the original feldspathic rock was of a fragmental 

 chai'acter. 



The alnindant iron-])earing minerals of the gneiss are horid)lende, bio- 

 tite, and chlorite. Less frequently epidote, sericite, and calcite occur. In a 

 single section any one of these minerals niav be predominant; two or more, 

 or all of them mav occur togrether. There seems to be al)solutelv no reii'u- 

 larity as to their occurrence, either in tlie field or in the sections themselves. 

 Hornlilende is, however, the pre})onderant nuneral in many sections, although 

 chlorite and biotite are hardh' less fre(|uently so. In the coarser grained 

 gneisses (PI. xv. Fig. 4) the hornblende often occurs iu large, well defined 

 crystals, which iu trans\'ei'se sections show either the planes of the prism 



