T. Sterry Hunt on Granitic Rocks. 117 
These strata, marked by the predominance of calcareous and 
magnesian silicates, appear, so far as known, to accompany 
each of the limestone formations of the Laurentian, sometimes, 
series, at which also occur the most numerous veins and the 
— minerals of economic value. It is also along these 
orizons, marked by softer rocks, that the valleys and the arable 
lands of the Laurentian areas are chiefly found, and for this 
reason, also, the mineralogy of these parts is better known than 
that of the harder gneissic portions. The above observations 
on the lithological character of the stratified rocks are 1mpor- 
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 Report 
of the Geological Survey of Canada for 1863-69, pages 181- 
calcite, sometimes with barytine and fluorite : these, which are 
of Paleozoic age or still younger, cut the Potsdam sandstone, 
the Calciferous sandrock, and probably also the overlying Tren- 
d ke bic veins with muscovite, 
tourmaline, zircon, etc. These veins I have describe as pass- 
ing by insensible gradations into the third class, in which calcite 
and apatite, with pyroxene, phlogopite and other calcareous and 
* This essay is reprinted, with some additions, in the Report of the Regents of 
the University of Nowe vox for 1867, Appendix E. The reader's attention 1s 
called to the note on the Hastings rocks at the close of this reprint. 
