158 GEOLOGY OF THE SECOND DISTRICT. 



Veins and other foreign minerids in this limestone. 



It is incorrect to call this a metalliferous rock, yet a few instances have occurred of its 

 containing lead and copper. The former is the sulphurct of lead, or galena ; and the latter is 

 also a sulphuret, forming the pyritous copper. No veins of either have yet been discovered, 

 but they both occur in small masses, and of little importance. 



A vein of quartz exists in Williamstown, traversing this rock with great regularity. It is 

 two feet wide, and its course is N. 54° W., with a steep dip. It is nearly a mass of pure 

 milky quartz, abounding in beautiful crystals which have some curious irregularities in the 

 extent of their faces. In a great proportion of them, there is a tendency to extend, so that the 

 remainder are nearly obliterated. 



The most interesting mineral in this limestone is albite, which occurs in Williamstovim, 

 (Mass.), Granville (N. Y.), Casdeton (Vt.), and probably at numerous other localities. It is 

 often transparent, and always in twin crystals. I have found them an inch in length, but 

 commonly only from one-fourth to one-half an inch. Calcareous spar, and brown or pearl 

 spar, are associated both with the quartz and feldspar. Sulphuret of iron, in simple unmo- 

 dified cubes, is of frequent occurrence, generally in the talcose and slaty varieties. Scales of 

 talc appear sprinkled upon the lamina through almost the whole mass. Brown tremolite is 

 also found in small bladed crystals, and in small confused groups. 



Note. I omitted to notice, in its proper place, the fact that native copper is occasionally found in 

 the Taconic slate. It was not my intention to speak particularly of the mineral contents of these rocks. 

 This led me also to pass over the galena in the sparry limestone, without a notice of it. 



4. Granular Quartz. 



This rock has a coiuposition quite homogeneous ; and though I have sometimes spoken of 

 it as a sandstone, still it hardly admits of this designation. Its particles are small siliceous 

 grains, slightly crystalline ; bat they do not appear to have been formed from abrasion of a 

 pree.xisting rock, like the ordinary sandstones. We cannot discover particles of mica, or any 

 angular or rounded fragments of older rocks. It is true that fine abraded particles, almost 

 impalpable, will, under pressure and other favorable circumstances, become homogeneous 

 and crystalline. 



There are two views which may be taken of this rock: 1st, that it is composed of the 

 fine debris of preexisting rocks abraded mechanically, and which have united and formed one 

 homogeneous mass ; or 2d, that this rock is the product of thermal springs, which of course 

 must have been large, and existed in the earlier era of the earth's history. 



Which of these views is the most rational, and most worthy of adoption, is difficult to 

 decide. In favor of the latter, it may be stated, 1st, that we find no particles of mica, or any 

 rounded particles which appear to have been rolled and ground by attrition, or to have existed 

 in other rocks, as granite or gneiss ; 2d, this rock lies along a disturbed district in which 



