CLA 



CLA 



and has a strong argillaceous odour. It 

 occurs in nodules, in a hard cellular horn 

 stone, that forms large mountainous masses 

 near Conway, in North Wales, and origi- 

 nates from the decomposition of indurat- 

 ed steatite. 



3. Clay from slate. Its colour is ash- 

 grey, passing into ochre-yellow : its tex- 

 ture is foliated : it has a smooth unctuous 

 feel, and its siliceous particles are so 

 small, as to occasion scarcely any gritti- 

 ness between the teeth. It occurs in 

 thin beds on the tops of the softer kinds 

 of slate-rock, and from its impervious- 

 ness to water is always found lining the 

 bottoms of the peat-mosses, with which 

 this kind of mountains is generally cover- 

 ed, and in these situations it is of- a white 

 ash colour, being deprived of its iron 

 and carbon by the acid of the peat. It 

 also occurs in thicker beds at the foot of 

 the mountains, but is of a darker colour, 

 and less plastic. 



4. Clay from shale. Its colour varies 

 from greyish blue to bluish black: its 

 texture is foliated : it has a smooth unc- 

 tuous feel, cakes a polish from the nail, 

 is excessively tenacious and ductile, and 

 has but a slight degree of grittiness. It 

 occurs abundantly in all collieries, and is 

 produced by the spontaneous decompo- 

 sition of the shale with which the beds of 

 coal are covered. A sandy clay, of a 

 greyer colour, and more refractory na- 

 ture, is procured from the decomposition 

 of the indurated clay that forms the 

 floor of the coal, and is provincialiy call- 

 ed clunch. The Stourbridge clay, from 

 which crucibles, glass-house pots, &c. are 

 made, is of this kind. 



5. Clay from trap. At the foot of the 

 softer rocks of trap-formation, such as 

 wakke, clay-porphyry, and some varie- 

 ties of grunstein and hornblende rock, 

 are found in beds of clay, evidently ori- 

 ginating from the gradual disintegration 

 of these by the weather. 



6. Marly clay. The colour of this is 

 bluish or brownish red : it occurs either 

 compactor foliated: it has a soft unc- 

 tuous feel, takes a polish by friction with 

 the nail, is very plastic, more or less 

 gritty, though not so much so as the com. 

 mon alluvial clay. It burns to a brick of 

 a buff or deep cream colour, and at a 

 high heat readily enters into fusion. It 

 effervesces strongly with acids, and con- 

 tains from one-fourth to one-tenth of 

 carbonated lime. It originates some- 

 times from the decomposition of com- 

 pact argillaceous lime-stone ; but more 

 frequently from the softer slaty varie- 

 ties usually called stone-marl. It is 



largely employed as a manure, and where 

 the calcareous part does not exceed 10 

 or 12 per cent, it is esteemed as a mate- 

 rial for bricks. 



7. Clay from metallic veins. Its colour 

 is grey, verging into bluish, greenish, 

 and yellowish, or red. It has a smooth 

 unctuous feel ; is very tenacious ; often 

 contains sulphuric acid, and certain me- 

 tallic oxides, which are never observed 

 in other clays, such as lead, silver, anti- 

 mony, copper and bismuth. Is found in 

 metallic veins. 



8. Alluvial clay. The circumstances 

 which characterize alluvial clay are the 

 following. It contains a larger propor- 

 tion of quartz sand than the preceding ; 

 rounded pebbles of various kinds are 

 also imbedded in it ; thus showing it to 

 have been carried from its native situa- 

 tion, and mingled in its progress with a 

 variety of extraneous bodies. At least 

 three kinds of it may be distinguished ; 

 viz. pipe clay, potter's clay, and chalky 

 clay. Pipe clay is of a greyish or yellow- 

 ish white colour, an earthy fracture, and 

 a smooth greasy feel ; it adheres pretty 

 strongly to the tongue ; is very plastic 

 and tenacious ; when burnt, is of a milk- 

 white colour ; is difficultly fusible, though 

 much more so than porcelain clay, from 

 which it is further distinguished by its 

 superior plasticity, and the sand which it 

 contains. It is manufactured into tobac- 

 co pipes, and is the basis of the white or 

 queen's-ware pottery. Potter's clay is 

 of a reddish, bluish, or greenish colour ; 

 has a somewhat fine earthy fracture, and 

 a soft, often greasy feel : it adheres to 

 the tongue, and is very plastic. It 

 burns to a hard, porous, red brick ; and 

 in a higher heat runs into a dark colour- 

 ed flag. When tempered with water, 

 and mixed with sand, it is manufactured 

 into bricks : those varieties that are 

 the most free from pebbles are made into 

 tiles, and coarse red pottery. See ALU- 

 MINA. 



CLAY stone t in mineralogy, is of a 

 greenish, bluish, or grey colour, some- 

 what marked by brownish yellow spots 

 and stripes. It occurs in mass, is opaque, 

 dull, frangible, and soft. It forms large 

 mountainous masses, occurring in beds 

 .and veins. 



CLAYTONIA, in botany, so named in 

 honour of Mr. John Clayton, a genus of 

 the Pentandria Monogynia class and or- 

 der. Natural order of Succulentae. Por- 

 tulaceze, Jussieu. Essential character: 

 calyx two valved ; corolla five petalled ; 

 stigma trifid ; capsule three valved, one- 

 celled, three-seeded. There are twr 



