174 GEOLOGY OF THE SECOND DISTRICT. 



avail ourselves of the ordinary means for dissolving the silex, as we have not the condition of 

 a thermal water, nor caloric to aid the solvent powers of the alkali. The following suggestion 

 is, however, offered in explanation of the phenomenon of the reproduction of silex in a solid 

 state, and often under crystalline forms : The silex being derived from the feldspar, the mo- 

 ment the potash leaves the comp und, the integrity of the mineral is lost, and the silex and 

 alumine then combine with sufficient water to give them mobility ; the silex is, however, 

 separated into its ultimate molecules, and as these cannot exist in a separate state, they recom- 

 bine either in grains or regular forms ; and these being still acted upon by molecular attrac- 

 tion, form the masses or nodules of which I have been speaking.* 



Whatever rationale may be offered in explanation of this interesting decomposition, we are 

 furnished with a beautiful instance of a natural and spontaneous decomposition or analysis of 

 feldspar, as complete and perfect as can be obtained in the laboratory of the chemist ; so per- 

 fect, indeed, that we. are able to perceive each element side by side in its particular repository, 

 with the exception of the potash, which has been removed in consequence of its ready solu- 

 bilitv, and its little disposition to enter into combination with silex and alumine without the 

 aid of heat. To assist our minds to comprehend more clearly the sequence of these move- 

 ments, which result in the formation of concretionary masses, we may consider all the elements 

 of feldspar as forming at one time a plastic movable mass like paste, and in which there is a 

 perfect intermixture of the materials, or the elements which composed the feldspar originally. 

 Under these circumstances, all the easily soluble matter as potash would be washed away, or 

 removed by infiltration through the earthy materials. Those which remain, will be left to be 

 acted upon by molecular attraction, which would be exerted between particles of the same 

 kind. This influence brings into closer union the particles of silex in the immediate vicinity 

 of each other ; and which, by a continuance of the same influence, would produce a gradual 

 accumulation of matter of increasing density and firmness, until finally those movements have 

 been imparted to the greater part of the silex in the beds. The accumulations commence at 

 niunerous points, which are dificrent centres of attraction, at each of which, there is formed 

 a mass of silex, or hornstone, or chalcedony. 



Analogous changes take place in the porcelain pulp, after the materials have been ground 

 and formed into a pasty mass in the vats, in case it is suffered to stand long without agitation ; 

 for after long repose, it is found that concretions of silex have formed, indicating the com- 

 mencement of a series of changes which would result in the production of solid siliceous 

 concretions, and which, if suffered to go on, would finally affect the entire constitution of the 

 mass, and completely spoil it for the purposes intended. 



The oxides of iron and manganese, which are usually associated in these beds, are derived 

 originally from the granite. In the beds they appear under two forms : first, as a coloring 

 matter, forming the yellow, red or pink-colored clays ; and secondly, as concretions which 

 have been formed by the same process as those composed of silex. 



* The decomposition probably arises from the strong affinity of potash for water: the alkali is therefore the vinculum which 

 holds the elements together. 



