ISi On the Porcelain Earth of Cornwall. [Marcet, 



into blocks resembling bricks, of tbe thickness of the mass in one 

 direction, and varying in their otlier dimensions : these bricks are 

 transferred to the shelves of a drying-house, or slied, which are 

 formed of wooden hais freely admitting tlie passage of the air 

 between thcra ; and when quite dry, the pieces are scraped perfectly 

 clean with an iron instrument, and the co.irser parts, containing 

 fragments of quartz and other impurities, wliich formed the bottom 

 of the mass, carefully removed. The pieces are then put into casks, 

 and broken down by ramming so as to fill them completelv, and 

 thus sent to the ])0tterlcs. The finished clay, when well prepared, 

 is of a beautiful and uniform whiteness, and breaks easily between 

 the fingers without grittiness. 



Ihe scrapings of the pieces dried under the shed, and the waste 

 of the packing, arc saved, and washed apart into a small pit near 

 the packing-house, the overflow of which runs into one of the laTge 

 ponds, the coarser matter being rc-jccted. 



There is some variety, at diHisrent works, in the relative extent 

 of the parts. At Trelliorsa, one of the largest, there were, I was 

 informed, in 1810, three small streams at which the clay was 

 washed ; and the water from each of these passed successively 

 througli three pits of three feet and a lialf in depth, two of whicli 

 wore six feet square, and the third nine feet by sis, the deposit of 

 tile last only being preserved and dried. Ail these pits were 

 arranged together in a sort of coait: and the wuer from tbe last 

 three was distributed into nine poinh, each about twenty feet by 

 twelve, and five feet deep ; from whence t!ie clay was laded into 

 sixteen pans, each forty-eight feet by tweh-e, and fourteen inches in 

 depth. In another work: there was one pit the deposit of wi.icli 

 was rejected, and two to receive its overflow, the sediment of wiiich, 

 or " mica," was dried apart, the dimensions of all three being five 

 feet by four, and four feet in depth: three smaller pans for drying 

 the " mica : " and four ponds, twenty feet by twelve, and four feet 

 deep, with four large pans in wliieh tlie " clay" was dried. 



The quantity of clay prepared annually at Trethorsa was in IS 10 

 supposed tobeaiiout 300 tons. There were then employed at that 

 work altogether thirteen person« : eight men in removing the over- 

 burden and raising the clay, whicli is paid for by the cubic fathom ; 

 three men or boys in washing; and two in attending to the ponds 

 and pans, and in packing, — the occupations of the last five varying 

 as the different stages of the process required ll.eir attendance. 



The only buildings attached to the works are, liie shed for drying 

 the clay, already mentioned, which is formed of timber, and open 

 on three sides ; and one that includes an office for the overseer, and 

 a store-room tor casks, &c. in which also the clay is [jacked. 



The water that supplies the works is derived from the streams 

 near which they are placed, and is carried off by subterraneous 

 channels, which in some instances lead to shafts communicating 

 with mine-adits in the rock beneath. 



