82 THE CHEMISTRY OF CREATION. 



composed, shows us which of its ingredients 

 goes to form the white clay spoken of. Un- 

 altered granite, upon analysis, is found to con- 

 sist of quartz, mica, and felspar. It is the latter 

 ingredient, as we have already noticed, which 

 undergoes decomposition by the influence of 

 water, carbonic acid, and air. Consequently, 

 the two others, quartz and mica, are left behind, 

 and form the heavy particles of the decomposing 

 rocks which remain after the white clay has been 

 washed away. 



Clay of every description is produced in the 

 same manner; yet, as is familiarly known, it 

 is only the best china which is of a pure white 

 colour. Common earthenware is more or less 

 yellowish, or brown, or even red. This does 

 not essentially depend upon any difference in 

 the mode of formation of the clay from which 

 it is made; it is all equally derived from the 

 decomposition of felspar, but arises simply from 

 the fact, that some rocks containing felspar 

 contain also iron, or other colouring matter, 

 which of course communicates its stain to the 

 clay obtained from it. 



Surprise has often been expressed how mines 

 of silver have been discovered in such extra- 

 ordinary situations as some of those on the 

 bleak summits of the Cordilleras of South 

 America. But a little consideration of the 



