360 



THE GEOLOGIST. 



The saddle-beds are recurrent tlirough the whole thickness of the 

 limestone series, and, at least, five sets of these beds are distinguished 

 in the neighbourhood of Alstonfield ; but, no certainty belongs to 

 this enumeration, inasmuch as the same strata are plicated in certain 

 parts and not in others. The saddle-beds are known to crop out at 

 the surface, and a clue is thereby afforded to and embraced by the 

 miner in searching for them below ; but it has been particularly re- 

 marked that the contortions are always more gentle above than in 

 depth, resolving themselves, generally, into a long swell very dif- 

 ferent from the rapid and closely associated folds of the same beds as 

 seen below the surface. In fig. 3 the dotted lines, y, z, represent 

 this gradual dying out of the folds of the beds a a at their crop a' a' ; 

 but I shall have presently occasion to refer again to this curious cir- 



Lign. 2. — Contortod beds of alterna^ting limestone and sliale strata, shovring the formation of 

 " saddles" and " saddle-joints." 



cumstanco. The breadth of the saddles from wing to wing, taken 

 midway above the trough, of course, varies greatly, but there is 

 something like an average, and which may be stated at forty feet. 

 The joints, both huckle and trough, run very regularly ; and it is 

 worthy of remark that they are always continued out of the beds 

 eitlier above or below. Their general du^ection is north-north-west 

 and south-south-east, which is also the direction of the joints, in a 

 large majority of cases, of the Mountain-limestone, in Derbyshire 

 and Staffordshire. The perpendicularity of the saddles themselves 

 on their line of strike (east and west) is a matter of some importance, 

 since by the way in which they are inclined so may the direction of 

 the maximum compressing force be ascertained : thus if the majority 

 of the saddles bear to the right, it is more than probable that the 

 greatest rcsisiancc was to the left, and that the force, whatever it 



