1862.] HULL CAEBONIEEEOUS STRATA. 143 



lines. The variations of development of the Carboniferous rocks have 

 been fully discussed by Sir H. De la Beche*, who shows that the 

 greatest vertical thickness is attained in Glamorganshire of 12,000 

 feet or more, while east of Bristol the same beds are only 5500 feet, 

 and in the Forest of Dean 3385 feet thick. 



To what extent the true Coal-measures once surmounted the culm- 

 measures of .Devonshire it is, of course, impossible to say; but, from 

 the position of these beds with reference to the Glamorganshire 

 coal-field, from which they are separated by an anticlinal axis, there 

 was probably a large amount of strata now lost by denudation. We 

 must, with Sir B.. Murchisonf, regard the culm-measures themselves 

 as the representatives of the Carboniferous Limestone, and probably 

 the Yoredale series and Millstone-grit ; but, as there are only thin 

 bands of hmestone, with Posidonomya Becheri, to represent the great 

 limestone formation of Bristol and Chepstow, it is evident the " sedi- 

 mentary " elements have predominated in Devonshire to the disad- 

 vantage of the calcareous. These changes I have endeavoured to 

 illustrate by means of the isometric curves. 



The Carboniferous series, therefore, to the north and to the south 

 of the barrier belong to two different systems, not of time, but of 

 circumstances. Their materials have been accumulated in nearly 

 opposite directions. The sources of these materials have been differ- 

 ent, and also the direction of the currents. That the Carboniferous 

 series was connected by sea, round the western extremity of the 

 barrier, is proved by identity of fossils in the limestones and Lower 

 Coal-measures of the North of England, Central Ireland, and South 

 Wales, &c. In each of these districts Pecten jpa-pyraceus and Gonia- 

 tites Listeri occur in the Lower Coal- series. The calcareous member 

 was more fully developed in the east than in the west, and extends 

 from Somersetshire into Erance and Belgium, until, as already stated, 

 it thins away on approaching the Hhine. 



3. NoETH Atlantic Continent. 



Eeaders of the works of Sir C. Lyell will recollect how that author, 

 in treating of the distribution of the Carboniferous rocks of North 

 America, shows that the sedimentary materials increase in thickness 

 and become coarser in texture as they approach the north-eastern 

 seaboard. Thus in Nova Scotia these materials attain, according 

 to Dr. Dawson, a thickness of 14,000 feet J, in which the limestones 

 play a subordinate part, as they do in Scotland. Erom the flanks of 

 the Alleghany range, westward and southward, into Central America, 

 the " sedimentary " strata gradually thin away, while the calcareous 

 as constantly augment in bulk, until, on reaching the Rocky Moun- 

 tains, they attain magnificent proportions §, forming, as shown by 

 Sir J. Bichardson and Dr. Hector, the huge and rugged masses of 

 the central range. The tendency of the calcareous and sedimentary 

 elements of the system to become developed in opposite directions is 

 therefore strongly marked over this Continent. 



^ Memoirs of the Geological Survey, vol. i. t " Siluria," 2nd edit. pp. 293-4. 

 I " Acadian Geology," § Quart. Journ. Geol. Soc. vol. xvii. 



