58 Prof. Sedgwick on the general Structure 



movements which produced the strike and dip of the Cumbrian mountains 

 as above described ? 



Thirdly. The form and direction of the dislocations in the coal fields on 

 the Bristol Channel bear little resemblance to those of the northern carboni- 

 ferous chain — a circumstance probably originating-, partly in the local nature 

 of the disturbing forces themselves, and partly in the fact that the application 

 of these forces in the two carboniferous regions was not contemporaneous. 



After the first elevation of the central carboniferous chain of the north, the 

 lowest division of the new red sandstone group {rothe-todte-liegende) was 

 immediately deposited. The movements of elevation were not merely followed 

 by, but were probably the mechanical causes of, this deposit ; which is com- 

 posed of sand, small pebbles, and other incoherent materials, drifted to the 

 outer and lower edges of the coal-fields ; even at this day is in many places 

 but imperfectly cemented; and contains, though rarely, a few drifted coal 

 plants*. In some districts it is perfectly conformable to the upper coal strata 

 on which it immediately rests, and seems to form a regular connecting link 

 between them and the overlying formations ; but, considered on the whole, 

 its position, as far as regards the inferior strata, is discordant. It was followed, 

 and perhaps interrupted, by movements of elevation, producing a considerable 

 derangement in its component beds, and, of course, also affecting the lower 

 formations ; and these movements were succeeded in several parts of York- 

 shire, and of the Cumbrian mountains, by deposits of magnesian conglo- 

 merate and magnesian limestone — unconformable both to the lower division 

 of the new red sandstone {rothe-todte-liegende) and to the coal measures f. 



Now the overlying deposits of the Bristol coal-fields are perfectly analogous 

 to the series in the North of England, which commences with the magnesian 

 conglomerate ; but they appear to contain no representative whatsoever of the 

 lower division of the new red sandstone. Hence we may, I think, conclude 

 (not hypothetically, but on direct physical evidence), 1. That the movements 

 which gave the final configuration to the coal-fields on the Bristol Channel 

 took place after the deposition of the lower red sandstone, and were probably 

 contemporaneous with the second system of movements in the North of En- 

 gland, before alluded to. 2. That the movements (prior to the existence of 

 the lower red sandstone or rothe-todte-liegende) which gave the chief impress 



* See Geol. Trans., Second Series, vol. iii. p. 64. Traces of vegetable fossils occur in this 

 deposit, on the coast of Cumberland, near Whitehaven. Stems of Equiseta and other vegetable 

 impressions have also been found in it at Hickleton in Yorkshire, by the Rev. W. Thorp of Don- 

 caster. I was unacquainted with these facts at the time the Memoir just quoted was composed. 



f See Geol. Trans., Second Series, vol. iii. PI. VI. figs. 3. 4. 5. 6. 



