LIME. 229 



site of Fort George, there are veins of calcareous spar in the blue limestone, which are often 

 of a very dark colour. Rarely regular crystalline forms are found. 



Washington County. Crystals of the lenticular form are found in crevices in the rock at 

 Baker's and Glen's falls. 



Westchester County. Some years since, an abundant locality of crystals of calcareous 

 spar, having the form of the cuhdide of Haiiy (Fig. 80), were obtained from a vein in the 

 primary rock, about half a mile south of the prison at Sing-Sing. Some of these crystals 

 were very large, and a mass made up of an aggregate of them weighed nearly one hundred 

 and fifty pounds. Similar crystals, but of much smaller size, are found in thin veins, in the 

 gneiss near Yonkers. They arc sometimes associated with analcime and iron pyrites, in 

 minute but highly finished crystals. 



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. In a 

 former part of this work (page 67), I have included under this head all those varieties of lime- 

 stone which are, or may be, employed for ornamental building purposes, and have noticed in 

 detail the principal localities which are known to occur in this State. I shall, therefore, only 

 introduce here a short description of this variety of carbonate of lime, and refer the reader, 

 who is desirous of further information, to the preceding part of this work just mentioned. 



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. 

 Colour various, owing to the admixture of foreign substances ; when white, it is more or 

 less translucent. Specific gravity very variable, ranging from 2.40 to 2.84; the crystalline 

 kinds being the most dense. 



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

 carbonic acid 43.56, and lime 56.44; but it often contains variable proportions of silica, 

 alumina and oxide of iron. 



Dolomite, which in the former part of this work was included under the head of Marble, 

 being a distinct mineral species, will be particularly described farther on. 



