MARBLE. 67 



are referable to the same agency. May not this be the decomposition of a compound of 

 sulphur and lime, or the metallic basis of lime, which may exist at different and unknown 

 depths ? But I shall leave these theoretical considerations, until I have completed the descrip- 

 tion of our sulphur springs. I will only add, that it is no objection to the explanation here 

 proposed, that sulphur springs occur throughout the whole series of New-York rocks, while 

 all the workable deposits of plaster are confined to one rock. 



MARBLE. 



The term Marble should perhaps be strictly confined to those varieties of carbonate of lime, 

 whether included under the head of granular or compact limestone, which are susceptible of 

 a polish, and some minerals of which carbonate of lime forms the principal ingredient. I 

 shall apply it, in the present work, to all those varieties of limestone, or those minerals com- 

 posed chiefly of carbonate of lime, which admit of being dressed or polished, and are em- 

 ployed for ornamental building purposes. 



Description. The foliated granular limestone, or crystalline marble, is made up of dis- 

 tinct angular concretions, with a lower lustre and transparency than calcareous spar. These 

 grains are of various sizes, from coarse to very fine. When this granular composition dis- 

 appears, it becomes the compact limestone, which has a splintery or conchoidal fracture. 



The specific gravity of marble is very variable, ranging from 2 . 40 to 2 . 84 ; the crystalline 

 kinds being the most dense. 



Colour various, owing to the admixture of foreign substances. When white, it is more or 

 less translucent. 



Composition. When pure, this variety has the same composition as calcareous spar, viz. 

 carbonic acid 43.56, and lime 56.44, in 100 parts. But it is seldom found in this state of 

 purity ; almost always it contains silica, alumina and oxide of iron, the proportions of which 

 sometimes reach ten or fifteen per cent. 



Dolomite. The granular marble usually known by this name, differs from the preceding in 

 composition, and in some other properties. It effervesces slowly in nitric acid ; possesses a 

 higher specific gravity than calcareous spar, and is a compound of carbonate of magnesia and 

 carbonate of lime in somewhat varying proportions. 



The following constitute the more important localities of marble in the State of New- York. 



Clinton County. In the vicinity of Plattsburgh, there is a great abundance of black 

 marble of the compact variety, containing organic remains. There is also a valuable quarry 

 of a similar marble in Chazy, near the lake, and nearly opposite to Isle La Motte, and it is 

 probably a continuation of the same range. When polished, it has a jet black surface, and is 

 of great beauty. 



Columbia County. Mr. Mather gives it as his opinion that beds of marble equal to those 

 of Stockbridge and Egremont, exist in Hillsdale and Copake in this county. These beds 

 furnish a marble, which, although dolomite, is highly esteemed. 



