LIMESTONE AND MARBLE 425 



in the more crystalline marbles, and are evident either by varia- 

 tion in color, or in the presence of foreign minerals, as mica, 

 quartz, hornblende, pyrite, etc. 



The variation in the strength and durability is as great as in 

 the composition and texture. Some are stronger than many 

 granites in their resistance to crushing force, and equally endur- 

 ing ; others consist of loosely cohering grains, and are friable 

 and rapidly dissolved by atmospheric agencies. The more sili- 

 cious and compact limestones are generally the more durable 

 and stronger ; in the marbles the well-crystallized and more 

 homogeneous texture consists with endurance and strength. 

 Both the magnesian and dolomitic varieties are good stone as is 

 proven by the Calciferous and the Niagara limestones, and in the 

 marbles of Tuckahoe and Pleasantville, in Westchester county. 



Crystalline limestones occur in New York city and Westches- 

 ter county, and in the Highlands of the Hudson. In the Adi- 

 rondack region there are numerous localities. The rock in many 

 of them is too impure and has too many foreign minerals 

 to admit of its use as marble. Quarries have been opened in 

 Westchester, Putnam and Dutchess counties, which have yielded 

 a large amount of fine white marble. In the northern part of 

 the State, the Port Henry and the Gouverneur quarries have been 

 productive. The geological horizon of some of these marbles is 

 in doubt. The belt in the eastern part of Dutchess and Putnam 

 counties belongs to the Yermont marble range, and is probably 

 metamorphosed Trenton limestone. The Westchester marbles 

 may be of the same age. 



The limestones which furnish building stone in this State are 

 the Calciferous, Chazy, Birdseye, Black Eiver, Trenton, Niagara, 

 Lower Helderberg, Upper Helderberg, or Corniferous, and Tully. 

 The geographical distribution is given in the following notes, and 

 in the order of geological succession, from the lowest to the 

 highest. 



Calciferous Sandrock. 



The rocks of the Calciferous formation in the Mohawk valley 

 and in the Champlain valley are more silicious than at the south- 

 west, in Orange county and in the Hudson valley, and hence the 

 designation as a sandrock. Much of it at the north is a limestone 

 rather than a sandstone, and may be termed a magnesian or silicio- 



