RAMBLES IN CORNWALL. 41 



Now, it is this felspar in the granite that furnishes 

 ns with China clay. It might seem an impossible 

 thing to a person with a lump of hard granite in 

 his hand to get the felspar out of it and to break 

 up that felspar into silica and potash at any such 

 cost as would make it worth while to do so. And 

 certainly it would be an utter impossibility for man 

 to x do this at anything like a remunerative outlay. 

 But Nature does the work without effort and without 

 expense. By certain natural processes, the felspar 

 of the granite is decomposed, and the rock is trans- 

 formed into a soft crumbling mass, which in many 

 places can be scooped out with the hand. The 

 potash and part of the silica are washed away, and 

 the silicate of alumina which remains constitutes 

 the China clay of commerce. China stone is this 

 same clay at a somewhat earlier stage in the process 

 of decomposition, when there is more of the quartz 

 mixed with it. Sometimes the clay comes nearly 

 up to the surface, but generally there is more or 

 less of sand and stones overlying it. This "over- 

 burden," as the covering is called, must, of course, 

 be removed before the clay is worked. 



As may be supposed, geologists and chemists 

 have taxed their ingenuity in order to account for 

 this remarkable dissolution of the granite and felspar. 

 Carbonic acid, one of the strongest solvents in nature, 

 was, of course, invoked to explain the phenomenon. 

 But why has not this agent led to the disintegration 

 of granite in other places ? Besides, could carbonic 

 acid act at such vast depths as those at which it is 

 known the clay occurs ? Mephitic vapours are also 



