202 BULLETIN OF THE NEW YORK STATE MUSEUM 



II. 



GEOLOGICAL POSITION AND GEOGRAPHICAL 

 DISTRIBUTION OF BUILDING STONE 

 IN NEW YORK 



I. Crystalline Rocks. 



Under this head there are the rocks which consist of one 

 mineral species, and are simple in composition, as the 

 limestones and marbles; and the more complex aggregates, 

 in which two or more minerals enter, as the granites, 

 gneisses, syenites, traps and other compound rocks. Since 

 rocks, unlike mineralogical species, do not have a definite 

 chemical composition, this subdivision is not based upon 

 sharply defined characters. It separates them however into 

 two classes, which include many species and kinds, whose 

 varieties by imperceptible gradations approximating one 

 another in composition, are still sufficiently well marked, to 

 be placed in one or the other of these divisions. There are 

 many varieties in the latter or compound class, differing 

 slightly from one another in mineralogical composition and 

 arrangement. And comparatively few of them are of eco- 

 nomic importance as building stone. 



A further subdivision of the compound crystalline rocks 

 is into massive and foliated, schistose, or bedded, according 

 as they occur in beds or are unstratified. The importance 

 of this division is evident, in the absence of lamination or 

 layers, in the homogeneous nature, and in the larger size of 

 blocks which are obtainable in the case of the massive rocks. 



Granites, Gneisses, Syenites, Trap-Rocks and Norites. 



I. Granites. Typical granite is a crystalline, granular mix- 

 ture of feldspar, quartz and mica. In addition to these 

 essential constituents, one or more accessory minerals may 



