120 THE WORLD'S LUMBER ROOM. 



looking as if they had just been freshly painted with 

 vermilion, and reminding one of the churches of North 

 Germany, and here again are piles of what look like 

 crumbled bricks and mountains of potsherds, such as that 

 of Monte Testaccio, near Rome, said to be composed of 

 the broken pottery thrown away by the Romans. 



Almost all the porcelain-clays are derived from the 

 felspar of granite rocks, and usually contain spangles of 

 mica. The soda or potash, having been attacked by the 

 carbonic acid of air or water, is readily dissolved and 

 washed away ; then the silicate of alumina which remains 

 is more slowly carried down the hill side in the form of 

 fine powder, some of which is deposited in beds along the 

 watercourses, while the finest and purest is carried into the 

 valleys, or into rivers and lakes. The farther it is carried 

 the more perfectly it is sorted, and hence the low-valley 

 clays are often wonderfully fine. 



The soil at the bottom of granite hills is, therefore, 

 usually too stiff, while that on the top is too sandy, to 

 be fertile. 



The granite hills of Cornwall and Devonshire supply 

 all the kaolin, or china-clay, used in the Staffordshire pot- 

 teries. This is the finest and purest white clay known, and 

 derives its name from Kaoling, "lofty ridge," the mountain 

 from which it is obtained by the Chinese, who seem to 

 have been the first to turn it to account. The place 

 whence the largest quantity is derived in England is the 

 neighbourhood of St. Austell, Cornwall, and when first 

 raised it has the appearance and consistency of mortar. 



China-stone, also used for making porcelain, is a product 



