bearing on theoretical Speculations. 405 



The carboniferous strata are very much and very generally 

 disturbed, but yet considerably less so than the subjacent 

 transition formations. Thus the strata of the Cross-fell chain 

 and the Durham coal-field seldom deviate by more then ten 

 degrees from the horizontal line, although often traversed 

 by very considerable faults, sometimes effecting dislocations 

 of nearly 1000 feet. The same remarks may be applied 

 to the Derbyshire coal-field. The South- Welsh coal-field is 

 very unequally disturbed : nothing can exceed the derange- 

 ments of the Pembrokeshire portion (see the sections in De 

 la Beche's memoir, Geol. Trans, second series, vol. i. In 

 Glamorganshire, the northern portion of the coal tract ge- 

 nerally presents but a low angle of inclination (about 12°): 

 but here occur several considerable faults, in connection with 

 which the strata become vertical and much contorted. In the 

 Southern portion the disturbance is more general, and the 

 angle varies from 45° to 70°. 



In the Somersetshire coal-field the disturbance is very con- 

 siderable, especially towards the Mendip chain, where the 

 limestone is often nearly vertical, and the superincumbent 

 coal beds thrown quite over, and doubled into zigzags. Near 

 Clevedon also a large tract of limestone covered with coal- 

 measures appears to have subsided to such an extent, that 

 near the line of fracture the subsided strata crop out three 

 miles to the west of the main chain with which they must orii 

 ginally have been continuous. 



On the Continent, the coal-measures about Valenciennes 

 and throughout the district of the Meuse exhibit the most re- 

 markable contortions and derangement (see Oeynhausen and 

 Decken's excellent Be7nerJcungen): such also appears to be ge- 

 nerally the case in Germany (see H. de Villefosse, RicJiesse 

 Miner ale de la Westphalie). 



These convulsions of the carboniferous beds are clearly all 

 referable to one single geological period ; — that, namely, of the 

 formation of these deposits ; for they do not extend * to the 

 next superincumbent formations of magnesian limestone and 

 new red sandstone, which, on the contrary, repose on them in 

 beds nearly horizontal ; so that an eminent geologist, Omalius 

 d'Halloy, assumes as the general division of the rocks of 

 which he treats ; 1st, inclined formations; viz. transition and 

 carboniferous : and, 2ndly, horizontal, including all the super- 

 strata. Nor, in fact, can we consider the principal period of 

 convulsion as having been coextensive with the whole period 



* There are indeed some faults which, as we shall presently see, affect 

 the coal rocks and the superstrata in common : but these do not bear to 

 the dislocations peculiar to the former, the proportion of 1 to 1000. 



of 



