Capt. Grant on the Geology of Cutch. 295 



clay, the impressions and remains of reeds, ferns, &c., the bands of ironstone, 

 the dislocations by dykes, slips, &c., all bear an analogy to the coal-fields of 

 England ; but I am inclined, from the vegetable remains, to consider this 

 deposit an equivalent of the oolitic coal of England, and not of the regular 

 carboniferous system. 



Alum Works near Mhurr. 



The ground on which Mhurr is built, consists of high, irregular banks of 

 marl of every variety of colour, but in a most confused and shattered state. 

 It is surrounded on three sides by steep hills, forming a kind of amphitheatre ; 

 and nothing can be more desolate than its appearance. North of the 

 town is a high table-land, which extends to some hills about one mile and a 

 half distant. It is composed, near their base, of a ferruginous quartzose 

 sandstone, on which the variegated marls rest; the latter being covered, in 

 many places, with a bed of coarse gravelly detritus, six or eight feet thick. 

 Imbedded in this gravel, are some very large masses of basalt, and of a very 

 hard, black stone, composed of grains of quartz cemented by an almost 

 black oxide. They are cut into mill-stones for grinding flour. The whole 

 are evidently boulders from the hills to the northward, which were mentioned 

 in the first part of this memoir, as consisting of quartz and basalt. This plain 

 terminates, to the southward, in a high bank overlooking the town, and 

 intersected in one part by a large dyke of spheroidal basalt, which has ap- 

 parently so indurated the strata of variegated marl in its vicinity, as to permit 

 them to be quarried for building. A large quantity of alum is made at this 

 place, and exported to ditferent parts of India. 



Manufacture. — The 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 is 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 substance 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 oflT, leaving an impure crystalline sediment. This is 

 once rhore boiled, and when it arrives at a proper state, which is learned by practice, it is poured 

 into large earthen vessels with a small mouth, and sunk into the ground to prevent their break- 

 ing. After a time, the vessels are dug out, broken to pieces, and a lump of pure alum extracted. 

 Six or eight measures, by weight, of alum, are produced from ten measures of the substance from 



