434 SCIENCE PROGRESS. 



of beds continuously along the strike," 1 and the explanation 

 of the same kind of phenomenon in a series of ordinary sedi- 

 ments would involve no exceptional conditions of sedimenta- 

 tion. A river flowing into an open lake or sea would 

 deposit a mass of sand and mud near its mouth, but in the 

 deeper and clearer waters the deposits would be made up 

 almost entirely of fine sediment, which would be spread out 

 over a much larger area ; thus building- up in the whole area 

 of sedimentation a series of beds, of which the heavier and 

 coarser materials would gradually preponderate in a direction 

 towards the source of supply. Regarded, therefore, as an 

 ordinary series of sedimentary deposits, the Staffordshire 

 sections are not difficult to interpret, but if we must adhere 

 to the theory of an intermittent subsidence taking place over 

 one part of a small area, and not over another, the reading 

 of the sections becomes a matter of much greater difficulty. 



This splitting of coal seams, which occurs on an un- 

 usually large scale in the Staffordshire coalfield, is of 

 frequent occurrence in other districts. 2 



The theory of a gradually sinking area, with periods of 

 subsidence alternating with intervals of rest and luxuriant 

 forest growth, was formulated by Bowman in 1840, and has 

 been accepted by Lyell and the majority of geologists as a 

 satisfactory method of explaining the blending and splitting 

 of coal seams. The more reasonable point of view is surely 

 that adopted by Beete Jukes, Grand' Eury, and other 

 writers, which regards the seams of coal as beds of vegetable 

 sediment, deposited under the same conditions as strata of 

 arenaceous and argillaceous materials. The regularity and 

 uniform character of coal beds is occasionally interrupted by 

 the occurrence of sandstone patches and other foreign 

 material, constituting the "rock and rig" or "rolls and 

 swells " of English miners. Such patches of sandstone offer 

 no great difficulty to the geologist who looks to the or- 

 dinary rules of sedimentation for an explanation of the facts ; 

 the " rolls and swells " are simply ridge-like accumulations of 

 sand or mud piled up on the floor of the area of deposition. 



1 Jukes, p. 19. 2 See Grand' Eury (2), Pis. xxii. and xxiv., etc. 



