414 The Thick Ooal of South Staffordshire. 



above the ten-yard seam only six to eight feet of coal is found, 

 and of this not more than one-half is workable. The ten-yard 

 coal has not, however, one uniform structure throughout. It 

 is, on the contrary, divided by partings of varying thickness 

 into from ten to fifteen distinct seams, each of which is so well 

 defined that a thick- coal collier will readily determine from 

 what part of the deposit any stray specimen of the coal has 

 been obtained. In the section recently exposed near to Dud- 

 ley the following divisions could be easily traced. The lowest 

 portion consisted of about three feet of benches coal, which is 

 usually cut away in the process of working. Above this was a 

 few inches of black indurated clay, or " batt." Eleven feet of 

 coal uninterruptedly succeeded ; but this contained the bottom 

 slipper, sawyer, and stone coals, each one very marked in its 

 physical character. A layer of stone came next, and upon that 

 nearly four feet of slips coal, so called from its brittle and un- 

 certain nature, and the number of accidents which arise from 

 this peculiarity. Succeeding this were foot coal, brassils (a 

 rough and impure layer, containing a considerable amount of 

 iron pyrites), tovj coal, white coal (a name of doubtful origin), 

 top-slipper, and roof coal, representing a total thickness of 

 between 18 and 19 feet, with partings of various kinds, occu- 

 pying nearly two feet. The aggregate thickness of the coal at 

 this place is considerably in excess of its average dimensions, 

 as the coal alone is above 36 feet from top to bottom. It 

 must not be inferred, however, that the different members 

 forming the ten-yard coal are always found in such close 

 proximity, separated by such insignificant partings. The 

 upper portions of the seam are frequently divided from the 

 underlying measures by from 10 to 130 feet of rocky material, 

 and form what is termed the " Flying Keed." Moreover, as 

 the coal-measures are traced northwards, towards the newly- 

 opened part of the field, near Cannock Chase, it is found that 

 the seams are much thinner and more numerous than in 

 the central and southern portions of the district. It is now 

 generally admitted that many of these thin measures are, in 

 all probability, the representatives of the several divisions of 

 the thick coal, only separated by shale and sand, owing to 

 peculiar conditions which prevailed in this part of the area 

 when the coal was originally deposited. It would be out of 

 place to enter here upon any examination of the theories which 

 have been advanced in order to account for the formation of 

 coal; but certainly the vast thickness of this, the principal 

 seam in the South Staffordshire field, presents no small diffi- 

 culties when we endeavour to explain its aggregation by any of 

 the usual suppositions. That the conditions under which the 

 various portions were formed differed very greatly must bo 



