BRITISH ASSOCIATION. 



2dl 



entire. At Bradford and at Ardwick, in the roof of thin coal 

 intercalated with the hmestones, the detached teeth, bones 

 and scales of fish occur, mingled with countless myriads of 

 the remains of Cypris and Microconchus. 



II. Coal and Cannel Seams. The author describes two 

 varieties of coal, the cubical where the cross cleavage runs at 

 right angles to the main cleavage, and the rhomboidal where 

 it makes an acute angle; the first form generally occurs in 

 the upper and lower portions of the field, the latter prevails 

 in the middle. The main cleaveage, he observes, is, in most 

 cases, parallel wdth the principal fault in the vicinity. The 

 beds of cannel are generally found on the top of the coal, and 

 nearly always contain remains of fishes, often bivalve shells, 

 but hitherto have exhibited no trace of Microconchus, and 

 rarely any leaves or stems of plants, whilst the upper por- 

 tion of coal seams frequently exhibit traces of Sigillariae, 

 Lepidodendra, Calamites, &c. The coal seams are either 

 simple, and continue undivided over large tracts of country 

 or split and divide into several distinct seams ; the form.er 

 generally occur in the lower portion of the field, the latter in 

 the middle and upper part. Independently of the tendency 

 to divide, many seams diminish in thickness till they become 

 evanescent ; this is chiefly observable in the lower division of 

 the coal-field, and in the simple seams six beds which have 

 been worked in that series, give decisive evidence of this 

 fact. The best examples are the caking coal of Rochdale and 

 the Foot mines, beds known by various names in different 

 parts of the country, but easily identified by the remarkable 

 nature of their floor, which is a hard crystalline stone, called 

 Gannister, full of Stigmaria ficoides, and employed as a 

 material for mending roads. At Dulesgate, near Todmorden, 

 the upper or " Gannister coal" is 5 feet 8 inches in thickness, 

 and the Foot coal, about 12 yards below it, is 7 inches thick ; 

 the author has traced these seams about 1 1 miles to Quarlton, 



VOL. I. NO. IX. X 



