SOUTH-WEST IRELAND. 201 



a horizontal mass of chalk over all the Weald, and 

 that consequently the North and South Downs sank, 

 or the Hastings beds were shoved up. It has already 

 been shown, that when a sheet of rock is bent into 

 anticlinal and synclinal curves, it may form unbroken 

 arches, or the strata may gape in places, and form 

 open fissures along lines of weakness, the gaps being 

 equal to the radii minus the cosines of the angles 

 of the slopes. This, in the case of the Weald, if we 

 ignore the minor flexures, and consider it one anticlinal, 

 would be 18 miles multiplied by 1 minus the cosine of 

 1 + 12 miles multiplied by 1 minus the cosine of 1, 

 which would give a valley only 25 feet wide from 

 escarpment to escarpment, if the beds opened to- 

 gether, which, however, is improbable, the different 

 groups of rocks being made up of such dissimilar 

 materials. In such a case, each bed would have re- 

 tained its relative position to its fellows ; but if the 

 beds were capable of bending without breaking, and 

 would not stretch, the original position of each would 

 have to change, as each bed must move on the one 

 below it up towards the axis of each anticlinal curve. 

 If, however, the upper beds were ruptured, while the 

 lower beds were not, it is not unreasonable to suppose, 

 especially if there was an upward as well as a hori- 

 zontal thrust, that the upper beds might remain 

 fixed at their unbroken ends, while the lower beds 

 would be pushed along below them, and up into the 



