WARREN COUNTY. 173 



Granite. 



The most important mass under tliis head, is in Athol, at the base and in the vicinity of 

 Crane's mountain. It is white, tolerabl)' coarse, and contains but a small proportion of mica. 

 The feldspar decomposes rapidly, and forms that important material called porcelain clay. A 

 very large proportion of the bed is in a crumbly decomposing state. The precise extent of 

 this kind of granite has not been ascertained ; it is, however, known to continue with little 

 interruption for nearly twenty miles. The importance of this rock is derived wholly from its 

 nature, and its ready conversion into clay. I shall therefore speak more of this product of 

 the rock, than of the rock itself. 



The characters which predominate in all granites which furnish this material for the finest 

 kind of pottery, are coarseness, with large plates of mica if any exists in the rock, and a 

 white flaky talc, which perhaps appears only as a coating to the feldspar. A great length of 

 time is required for the production of the clay ; for the changes which the materials pass 

 through are slow and gradual, and are effected by slow molecular attraction, whicii in the 

 first place dissolves the tie that holds the mass together, and is preparatory to those nicer 

 changes by which the potash is liberated from the feldspar, and the silex and alumine in- 

 timately blended in a soft snow-white mixture. Feldspar, which furnishes the clay, is 

 composed of silex 64, alumine 20, potash 14, lime 2, or sometimes only a trace of the last 

 substance. It is to the large qu amity of potash that we arc to attribute those changes which 

 result in the formation of porcelain clay. The beds are not composed, as we should expect, 

 of one homogeneous mass, but consist of layers of different colors ; white, yellow and red 

 predominating. Sometimes the distribution into layers is imperfect, and the white and valu- 

 able portion occurs in masses. In addition to the colored clays, the beds contain particles of 

 quartz, nodules of manganese, and, what are quite interesting, large nodular masses of silex, 

 of a secondary formation. 



It will be observed from these facts, that the changes are of an interesting as well as of a 

 complicated character. It will be useful to occupy a moment in an exposition of these 

 changes, and the sequence in which they occur. We must first state one or two facts in rela- 

 tion to the solubility of silex. This substance, as it exists in rock crystal, when pulverized 

 to a dust as fine as possible, is extremely insoluble by all the ordinary agencies. By means 

 of potash or either of the alkalies, aided by heat, it is rendered highly soluble ; and while in 

 this combination, weak muriatic acid, or even water, is also capable of holding it in solution. 

 Silex is also contained in thermal waters ; and when these are exposed to the air, and lose 

 their temperature, the silex is deposited or precipitated in the form of a tough porous rock, 

 around the places where the springs issue. In the formation of porcelain clay, which con- 

 sists of alumine and silex, there is a loss simply of the potash ; the production of which may 

 be accounted for by a solution of the whole or part of the potash by the water. But to account 

 for the regeneration of silex in a solid concretionary state, and even its crystallization as is 

 found to be the case in the interior of these nodules, is not so easy a matter ; for we cannot 



