S16 



On the Geology of Cuich. 



[Oct. 



quarried for building. A large quantity of alum is made at this place, 

 and exported to different parts of India. 



Manufacture.— l^he shale from which alum is obtained, forms beds in 

 the variegated marl ; and in a kind of blue clay. Long galleries are 

 cut for the purpose of extracting it ; but so plentiful is the supply, that 

 no means are taken to support them, and they generally fall in during 

 the rainy season. The manner in which the alum is prepared is very 

 simple. The earth U exposed in heaps to the sun and air for about 

 five months, during which it burns spontaneously. It is next laid out 

 in little beds similar to those of a field prepared for irrigation, and it is 

 watered by a small stream for ten or fifteen days, by which time the 

 aluminous matter accumulates into semi-crystalline plates. This sub- 

 stance is boiled in water for about seven hours ; after which, a third, 

 or one half, by weight, of potash is added, and it is again boiled for a 

 few hours, according to the strength of the ley. It is then poured into 

 large open vessels, where, after settling for some time, it is washed, and 

 the liquid drawn off, leaving an impure crystalline sediment. This is 

 once more boiled, and when it arrives at a proper state, 'which is learned 

 by practire, it is poured into large eartben vessels with a small mouth, 

 and sur k into the ground to prevent their breaking. After a time, the 

 vessels are dug out, broken to pieces, and a lump of pure alum extract- 

 ed. Six or eight measures, by weiglit, of alum, are produced from ten 

 inea=:ures of the substance from the irrigating beds, and four or five 

 measures of potash. It is not so much esteemed in the Bombay market 

 -as that brought from China, on account of its yellow tinge. 



Some of the marls resemble chalk, being white, and soiling the fingers ; 

 and some are very calcareous, whilst other varieties scarcely effervesce 

 with diluted muriatic acid. In one mass I found a very minute s\)e(A- 

 men Buccinum pumilum. These marls also occur of every variety of 

 co'our as well as texture ; some of them consisting of innumerable thin 

 laminae curiously twisted and arranged in the most intricate manner; 

 -aMd others of a kind of breccia, composed of small broken portions of 

 marls. Several dykes of basalt cut through these beds ; the whole pre- 

 senting a most confused assemblage, partly due to natural causes, and 

 partly to the numerous mines which have fallen in. One of the banks 

 Jias been burning spontaneously for several years, in a similar manner to 

 that at Ruttrea, and apparently from the same cause. The exact geolo- 

 gical position of these marls I could not determine. 



