20 Report on Building Stone of New York. 



2. LIMESTONES. 



Limestone is essentially carbonate of lime, but it always contains 

 some additional constituent : and the more commonly occurring im- 

 purities, or accessory matters are silica in the form of quartz, clay, 

 iron and magnesia. And limestones are said to be siliceous, argilla- 

 ceous, ferruginous, magnesian and dolomitic, according as they con- 

 tain one or another of these constituents. Other foreign mineral 

 matter may be found in them, and in places so as to give character to 

 the mass. The texture also varies greatly. It may be coarse or fine 

 crystalline, sub-crystalline, or amorphous, according as the crystals 

 which make up the mass are larger or smaller, or are not recognizable 

 by the unaided eye. The terms coarse-grained and fine-grained may 

 apply when the mass resembles sandstone in its granular aggregation. 

 And it may be hard and compact, almost vitreous, or loosely ce- 

 mented and crumbling with slight pressure like sugar, or, again, like 

 chalk, dull and earthy. From this general statement of the range in 

 composition and texture, it follows that there is an equally wide vari- 

 ation in the hardness, strength and durability of limestones. Some 

 are hard and strong, surpassing in their resistance to crushing force, 

 many granites, and nearly as durable as the best sandstone ; others 

 are friable and fall to pieces under slight pressure, or they are dis- 

 solved rapidly by atmospheric agents. Wherever the admixture of 

 silica is large and the texture is compact, the stone is hard and 

 durable ; hence the siliceous limestones are generally among the most 

 enduring building stones. The magnesian and dolomitic varieties 

 also are good stone. In color the prevailing shades are grey-blue, 

 and yellow to white. As stated on a previous page, the limestones 

 which are quarried for building stone in this State are found in the 

 following named formations : Calciferous, Chazy, Trenton, Niagara, 

 Lower Helderberg, Upper Helderberg or Corniferous and Tully 

 limestones. The geographical distribution of the several limestone 

 formations is here given in the same order — that of the geological 

 succession, beginning with the Calciferous sandrock. 



Calciferous. 



Although termed a Calciferous sand-rock, very much of the rock 

 thus designated is, properly, a magnesian or a siliceo-magnesian lime- 

 stone. Some of the blue limestone which is quarried in Orange 

 county and the New Hamburgh quarry in Dutchess county are prob- 

 ably of this epoch. The calciferous is traced along the Mohawk 



