GEOLOGICAL POSITION AND GEOGRAPHICAL DISTRIBUTION 209 



is often markedly apparent at a glance. Similar differences 

 in composition are seen in the more crystalline marbles, and 

 are evident either by variation 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 enduring ; others consist of loosely cohering grains, 

 and are friable and rapidly dissolved by atmospheric agen- 

 cies. The more siliceous and compact limestones are gen- 

 erally 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 West- 

 chester county, and In the Highlands of the Hudson. In 

 the Adirondack 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 coun- 

 ties belongs to the Vermont 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 River, Trenton, 

 Niagara, Lower Helderberg, Upper Helderberg or Cornif- 

 erous and Tully. The geographical distribution is given in 

 the following notes, and in the order of geological succes- 

 sion, from the lowest to the highest. 

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