198 THE CRYSTAL FALLS IRON-BEARING DISTRICT. 



looked i;pon as tlie product of mineralizers, dependent upon the presence- 

 of the hot granite injection, to wliose action may also be referred the 

 jjresence of the tourmaline. 



The line of contact lietween the granite and the sedimentary frag- 

 ments, thoug'h somewhat irreg'ular, is macroscopically very well defined bj' 

 the difference in size of the mineral constituents of the two rocks. Here 

 and there in the fragments there are seen thin masses of the granite which 

 wH^re injected along the planes of sedimentation, and also traverse cracks 

 penetrating the sediments. On the granite side of such a contact there is a 

 narrow zone A'ery noticeably richer in large biotite flakes than the granite 

 is ordinarilv. No difference can be noticed on the sedimentary side of the 

 contact. The microscopical examination of the contact emphasized the 

 endogenous character of the metamorphic action. There is more biotite 

 present than in the normal granite. 



The feldspar in the normal granite has a decided tendency toward 

 automorphic development. Where the feldspars of the granite touch the 

 metamorphosed sediments they are partly rounded, and the mica plates 

 developed in the sediments have in general a parallel structure around that 

 side of the feldspar which is turned toward the fragments. 



At another point the quartz of the granite, where it comes in contact 

 with the sediments, has developed as an automorphic individual, and looks 

 as though it were pressed into the fragment. The quartz crystal contains 

 near its edge grains of feldspar and flakes of mica, thus making an imper- 

 fect narrow^ poikilitic zone. Beyond this zone there is the sedimentary rock 

 proper, and there the mica plates lie parallel to the contours of the quartz. 

 An illustration of such a contact is shown in figs. A and B, PI. XXXV, as 

 seen in ordinary light and also between crossed nicols. 



It appears that the formation of the quartz and feldspar noted above 



caused the arrangement of the constituents of the gneiss parallel to their 



contours. It would thus seem probable that in this particular case the 



recrystallization of the original graywacke into the gneiss which we noAV 



find in its place followed and was chiefly the result of the intrusion of the 



granite. 



BASIC IIS^TRUSIVBS. 



The basic intrusives are represented by raetadolerites and metabasalts. 

 The dolerites are the most important, and will be treated in detail. Rocks. 



