XL] GRANITES AND GRANITIC VEIN-STONES. 187 



ordinary micaceous, hornblendic, and binary granites to finely 

 granular and even impalpable mixtures of the constituent min- 

 erals, constituting the rocks known as felsite, eurite, and petro- 

 silex. These rocks are often porphyritic from the presence of 

 crystals of orthoclase, and sometimes of crystals or grains of 

 quartz imbedded in the finely granular or impalpable paste. 

 These felsites and felsite-porphyries (orthophyres) are, in very 

 many cases at least, stratified or indigenous rocks, and they are 

 sometimes found associated with granular aggregates of different 

 degrees of coarseness, which show a transition from true felsites 

 into granitic gneisses. The resemblances in ultimate composi- 

 tion between felsites, granites, and granitic gneisses are so close 

 that it cannot be doubted that their differences are only struc- 

 tural. 



5. Felsites and felsite-porphyries or orthophyres are well 

 known in eastern Massachusetts, at Lynn, Saugus, Marblelu-ad, 

 and Newburyport, and may be traced from Machias and East- 

 port in Maine, along the southern coast of New Brunswick to 

 the head of the Bay of Fundy, with great uniformity of type, 

 though in every place subject to considerable variations, from 

 a compact jasper-like rock to more or less coarsely granular va- 

 rieties, all of which are often porphyritic from feldspar crystals, 

 and sometimes include grains or crystals of quartz. The colors 

 of these rocks are generally some shade of red, varying from 

 flesh-red to purple ; pale yellow, gray, greenish, and even black 

 varieties are however occasionally met with. These rocks are, 

 throughout this region, distinctly stratified, and are closely as- 

 sociated with dioritic, chloritic, and epidotic strata. They ap- 

 parently belong, like these, to the great Huronian system. 



[Stratiform rocks, seemingly identical with these quartziferous 

 feldspar-porphyries, abound in Missouri, where they are asso- 

 ciated with the iron-ores of Iron Mountain and Shepard Moun- 

 tain. I have also found them over a considerable area along 

 the north shore of Lake Superior, on an island south of St. Ig- 

 nace, and for some distance along the coast to the southwest. 

 The breccia and conglomerate in which is found the native 

 copper of the Calumet and Hecla and the Boston and Albany 



