436 



J. Prestwich, Esq., on the 



Sometimes iron pyrites forms layers three or four inches thick ; at other times it is mixed with 

 coal in minute, invisible particles. The presence of this mineral renders the coal unfit for the re- 

 ducing of the ironstone. At Kingslow, the " sulphur coal", which contains much black and brown 

 mineral charcoal, is often beautifully iridescent*. 



Vegetable impressions may occasionally be detected in some of the coals ; and I have a speci- 

 men of the " best coal " which exhibits a very sharp and distinct impression of a portion of a palm- 

 leaf. Imperfect remains of vegetables, in the state of charcoal, are not uncommon, especially in 

 the "fungous coal", of which they sometimes constitute the larger portion. 



The " clod coal" is the best in the district, both for general use and for the iron furnaces. The 

 " middle and best, or Randle coals", which almost immediately overlie it, are also good coals, but 

 are rarely fit for the manufacture of iron. The " fungous coal", which is confined to the north of 

 the field, is also excellent for every purpose. The " top and double coals" are equally valuable. The 

 " flint coal" is good and serviceable, but cannot be used in the iron furnaces ; neither can the "little 

 flint coal", which is much worked in the southern districts, but it is not equally good in the north 

 of the coal-field t- All the coals have a distinct line of cleavage, at right angles to which the 

 miners always proceed when possible. These joints are vertical to the lamination, and are inva- 

 riably W.N.W. and E.S.E. An imperfect set of joints runs at right angles to this system. Some- 

 times, however, as in the " sulphur coal" at Ketley Bank, both are equally developed. 



Iron is abundantly diff'used throughout the whole of the coal-measures, but it prevails in some 

 strata more than in others. Almost all the sandstones are tinged, spotted, or striped by the per- 

 oxide of iron, which hardens the rock ; and consequently, when its surface is exposed to the atmo- 

 sphere, these ferruginous patches stand out in relief. 



In the shale beds, in which it occurs in the greatest abundance, it consists of argillaceous car- 

 bonate of iron, in flattish nodules, of variable size, form, and specific gravity. All the workable 

 ores are procured from these beds, with the exception of the " Crawstone", or lowest measure, 

 which forms irregular large masses in a finely-grained sandstone. This measure is of much better 

 quality in the southern than in the northern division of the coal-field. 



Proceeding upwards the " Penneystone" nodules are generally small, flat, and smooth; but they 

 increase in size and number as they approach the top of the stratum, where they not unfrequently 

 form a capping of solid layers. 



The "white flats" are in a hard shale, and consist of small, light-coloured, and rather rough 

 nodules. 



* I have made a proximate analysis of the principal coals of Coalbrook Dale, and found that 

 100 parts of coal consist of the following component parts : 



Names and Locality. 



Volatile 

 Substances. 



Carbon. 



Ashes. 



Colour of Ashes. 



Sp. gra. 



Fungous coal.— Donnington. . 

 Top coal. — Ditto 



34-8 

 .'37-1 

 34-6 

 41-1 

 34-3 



38-3 



63-8 

 62-1 

 64-9 

 56-1 

 64-4 

 62-7 

 61-1 



1-4 

 0-8 

 0-5 

 2-8 

 1-3 

 1-0 

 0-9 



White tinged brown. 



Very light brown. 



Fawn. 



Brown. 



Light dirty yellow. 



Ditto darker. 



Burnt umber. 



1-245 

 1-267 

 1-269 

 1-292 

 1-273 

 1-264 



7 



Flint coal — Madeley 



Sulphur coal. — Ketley 



Best coal — Madeley 



Little flint-coal. — Broseley . . 



t See Dr. Townson's Descriptions. 



