208 GRANITES AND GRANITIC VEIN-STONES. [XI. 



that of the harder gneissic portions. The above observations 

 on the lithological character of the stratified rocks are impor- 

 tant on account of the relations between these and the included 

 veins, in which the characteristic minerals of the gneissic and 

 calcareous rocks are often found associated. 



35. The history of these veins, as seen in the Laurentian 

 rocks of the Laurentides in Canada, the Adirondacks of northern 

 New York, and the Highlands of southern New York and New 

 Jersey, has been discussed at length by the author in an essay 

 on The Mineralogy of the Laurentian Limestones, in the Eeport 

 of the Geological Survey of Canada for 1863-66, pages 181 - 

 223.* In this essay, which will be frequently referred to in 

 the present paper, the vein-stones found in the Laurentian rocks 

 have been noticed under three heads : First, metalliferous veins 

 carrying galenite, blende, pyrite, and chalcopyrite in a gangue of 

 calcite, sometimes with celestine and fluorite ; these, which are 

 of palaeozoic age or still younger, cut the Potsdam sandstone, the 

 Calciferous sand-rock, and probably also the overlying Trenton 

 limestones. Second, quartzo-feldspathic veins with muscovite, 

 tourmaline, zircon, etc. These veins I have described as passing 

 by insensible gradations into the third class, in which calcite 

 and apatite, with pyroxene, phlogopite, and other calcareous and 

 magnesian silicates predominate, though frequently accompa- 

 nied by quartz and orthoclase. These veins are older than the 

 Potsdam sandstone, which rests upon their eroded outcrops, 

 and sometimes includes worn fragments of apatite derived from 

 them. 



36. It is these last two classes which it is proposed to con- 

 sider in the present paper under the name of granitic vein-stones. 

 In justification of the extension of the term "granitic " to the 

 whole of this series of veins, it must be repeated, that it is not 

 possible to draw a line of distinction between those in which 

 quartz and orthoclase are the characteristic minerals, and those 

 in which calcite, apatite, pyroxene, and phlogopite prevail, 



* This essay is reprinted, with some additions, in the Report of the Regents 

 of the University of New York for 1867, Appendix E. The reader's attention 

 is called to the note on the Hastings rocks, at the close of that reprint. 



