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a greater variety of manufactures than any other in Scotland, in this 

 department. The aluminous shale, or "alum till," lies between the 

 sulphureous coal below, and main limestone above, and is no more 

 than from 2 to 3 feet thick. There is first (ascending) an aluminous 

 band containing iron pyrites, and passing in some parts of the mines 

 into an imperfect blackband ironstone. Over this is the "gentle 

 slate," or principal aluminous band, 6 or 7 inches thick. The 

 uppermost band, called the " diamond" bed, from being studded with 

 crystals of pyrites, is much poorer in aluminous matter and is seldom 

 used, except to mix with the first or pyritous band. The main lime- 

 stone rests on this band in the mines ; but westwards on the south 

 hill the aluminous strata thin out, and the limestone then reposes 

 upon the sulphureous coal. On the north hill the shale bed is 15 feet 

 thick ; but the lower portion only is aluminous, and much poorer in 

 the "ore." The strata, however, are an exact counterpart of those 

 on the south hill. The upper part of the shale on the north hill is 

 charged with multitudes of marine shells. The chief difference at 

 Huiiet consists in the more equal distribution of the aluminous matter 

 throughout the whole thickness of the shale ; but there is over the 

 limestone a thick stratum, called the dough or duff bed, rather poorer in 

 sulphur than the alum schist. The schist here shows, when effloresced, 

 long brittle crystals of sulphate of magnesia ; which are rarely met with 

 in the Campsie ore. After the underlying coal is wrought out, the 

 alum schist decomposes under the action of the air, exfoliates and 

 falls down. Its sulphur, by the action of oxygen, combines with the 

 metallic bases, forming sulphates. When decomposition is complete, 

 the mass has the appearance of flock silk. The schist in this state 

 is taken from the coal wastes and lixiviated in stone cisterns. The 

 liquid is then evaporated to the proper density, and receives the por- 

 tion of muriate or sulphate of potash necessary to its formation into 

 the state of a crystallizable salt. This forms the sulphate of alumina, 

 or alum of commerce. Of late years this salt has been developed by 

 slow combustion in long ridges, coated with the exhausted ore; 

 which is found a quicker process. 



The extraordinary mass of coal at Quarrelton, near Johnstone, 

 which attains a maximum thickness of 90 feet, but is generally 50 

 to 60 feet, seems to belong to these lower divisions. It lies in a 

 basin-shaped cavity, less than 1 mile in diameter, and consists of 5 

 distinct seams, separated by thin layers of shale, sandstone, or iron- 

 stone. Over the coal is a stratum of sandstone, 24 feet thick, and 

 this is covered by blue basalt, 100 feet thick. This prodigious mass 

 of coal, perhaps the thickest ever found, seems to have originated 



