But before we bring this chapter on granite and its kindred rocks to a close, we must glance at one more purpose served by this Plutonic rock. Here is a teacup, and here is a piece of granite: the one comes from Cornwall, the other is made in Staffordshire or Worcestershire. What relation have they to each other? If it were not thought _infra dig._, we should say the granite is the parent of the teacup. In Cornwall, especially in the neighbourhood of St. Austel, the writer has lately visited what are called the China clay works. “The granite is here in a state of partial decomposition. In some localities, this _growan_” (Cornish for disintegrated granite) “is tolerably firm, when it resembles the Chinese _Kaolin_, and, quarried under the name of China stone, is extensively employed in the potteries. This is ready for the market when cut into blocks of a size convenient for transport; but the softer material, which is dug out of pits, and called _China clay_, or _porcelain earth_, requires a more elaborate preparation for the purpose of separating the quartz, schorl, or mica from the finer particles of the decomposed feldspar. This clay is dug up in _stopes_ or layers, which resemble a flight of irregular stairs. A heap of it is then placed upon an inclined platform, under a small fall of water, and repeatedly stirred with a _piggle_ and shovel, by which means the whole is gradually carried down by the water in a state of suspension. The heavy and useless parts collect in a trench below the platform; while the China clay, carried forward through a series of _catch-pits_ or tanks, in which the grosser particles are deposited, is ultimately accumulated in larger pits, called _ponds_, from which the clear supernatant water is from time to time withdrawn. As soon as these ponds are filled with clay, they are drained, and the porcelain earth is removed to _pans_, in which it remains undisturbed until sufficiently consolidated to be cut into oblong masses. These are carried to a roofed building, through which the air can freely pass, and dried completely for the market. When dry they are scraped perfectly clean, packed in casks, and carried to one of the adjacent ports, to be shipped for the potteries.”[24] As furnishing some idea of the extent to which this business is carried on, it may be added that 37,000 tons of this China clay are annually shipped from the south-west of England to the potteries, the value of which is upwards of £50,000, while the number of working men and women thus employed is beyond calculation. This is one of the practical results of geology. This is one of the things which geology, once a neglected and unpopular science, has done for our comfort and welfare. “A hundred years ago, it does not seem that any part of this China clay was made use of, or that this important produce was then of any value whatever.”[25]