30 DE. THOMAS STEERY HUNT ON THE 



other times imbedded in quartz, which covers the latter. Drusy cavities are also lined 

 with small crystals of the feldspar, and have been subsequently filled up by a cleavable 

 bitter-spar," often with crystallized hematite, rutile, and copper-sulphids. It was shown 

 that among these veins, then described as of aqueous origin, there was to be seen a transi- 

 tion, from those " containing only quartz and bitter-spar, with a little chlorite or talc, 

 through others in which orthoclase appears, and gradually predominates, until we arrive at 

 veins made up of quartz and feldspar, sometimes including mica, and having the character 

 of a coarse-grained granite ; the occasional presence of copper-sulphids and hematite char- 

 acterising all of them alike." There was also described the occurrence, in the same region, of 

 a dark-colored argillaceous and schistose rock, having in parts the aspect of a chloritic 

 greenstone, which is rendered amygdaloidal by the presence of numerous spherical or 

 ovoidal masses of quartz, or more commonly of reddish orthoclase, often with a nucleus of 

 quartz. In schistose varieties of this rock the feldspar extends from these centres in such 

 a manner as to give a gneissoid aspect to the mass. All of these facts were regarded as 

 showing the aqueous origin of orthoclase, and its secretion from the adjacent rock.'^ 



§ 59. With the feldspar in the above mentioned veins may be compared the similar 

 occurrence, observed in 18*72, in the great quartz lodes with chalcopyrite which traverse 

 the Hurouiau greenstones at the Bruce Mines, on Lake Huron, of bands one or two inches 

 wide of a brick-red orthoclase, mingled with a little quartz and a small amount of a 

 greenish, apparently hornblendic element, forming an aggregate which can hardly be dis- 

 tinguished from some of the older granitic rocks, but is clearly interbanded with the 

 metalliferous quartz and the bitter-spar of the lode. In this connection may also be quoted 

 a description of the vertical parallel veins found cutting at right angles the Montalban 

 gneisses, in Northbridge, near Worcester, Massachusetts. These veins, as described by the 

 writer, "may be traced for considerable distances, and are ordinarily but a few inches in 

 thickness. The veinstone of these is generally a vitreous quartz, which in some parts 

 exhibits selvages, and in others bands of white orthoclase, by an admixture of which it 

 passes elsewhere into a well characterized granitic vein. The quartz veins, in places, hold 

 cubic crystals of pyrite, together with chalcopyrite and pyrrhotite, the latter in consider- 

 able masses, sometimes accompanied by crystals of greenish epidote, imbedded in the 

 quartz, and occasionally associated with red garnet. In one part, there is found enclosed 

 in the wider portion of a vein, between bands of vitreous quartz, a lenticular mass, three 

 inches thick, of coarsely granular pink calcite, with imbedded grains of dark-green amphi- 

 bole and on one side small crystals of olive-green epidote and red garnet ; the whole 

 mass closely resembling some crystalline limestones from the Laureutian," and evidently 

 endogenous.'* I have also described remarkable examples of similar associations of 

 zoisite, garnet, hornblende, pyroxene and calcite in the metalliferous quartz lodes in the 

 Montalban series, at Ducktown, Tennessee." 



§ 60. The question of the aqueous origin of concretionary veins was resumed by the 

 author in 1871, in an essay On Grianites and Grranite Veinstones, when it was maintained 

 that the relation of granitic veins with metalliferous quartz-lodes, on the one hand, and 



^5 Geology of Canada, 1863 ; pp. 476 and 606. 



'^ Azoic Rocka, Report E, Second Geological Survey of Pennsylvania, p. 247. 



" Chemical and Geological Essays, p. 217. 



