56 CONTORTED STRATA IN THE YOREDALE ROCKS, NEAR ASHOVER. 



have observed the sections, the gritstone has been stripped away 

 from above, and the limestone below covered from sight. But in 

 all these cases, the neighbouring gritstones and limestones where 

 exposed are free from contortion. For instance, along the Amber 

 the gritstone that crests the sides and sweeps around the head 

 of the valley ; the Yoredales, when otherwise placed than in the 

 bottom of the valley ; and the limestone that comes to light 

 half a-mile nearer Ashover, partake only of tlie general curvature 

 of the anticline. I'here can be little doubt, then, that these 

 contortions are peculiar to the Yoredales of these districts. 



A glance at the accompanying diagrammatic section across this 

 part of the Amber valley will enable the reader to better under- 

 stand the conditions of these contortions, and will suggest a clue 

 as to their origin. The Yoredales (c) are there seen lying upon 

 the Mountain limestone (b), and ovedaid by the Millstone grit (d), 

 the contortions being represented at (a). On the S.W. side is the 

 broad elevated tract of Darley Moor, and on the N.E. the high 

 ground above Amber House. 



The Yoredale shales are a friable and yielding rock, and it 

 will be observed that here they are squeezed between two harder 

 and less yielding series of strata. Now we know that a yielding 

 body, such as putty or stiff dough, when placed under a weight 

 will spread out sideways. Movements of a similar nature in the 

 softer rocks, as clays and shales in mines, are well known to 

 miners as " creeps." Upon a similar principle, the heavy masses 

 of gritstone of Darley Moor and Amber House must tend to 

 press out the soft Yoredales below ; and where the latter meet 

 with no lateral resistance, as at the outcrop in the sides of the 

 valley, there must consequently be a " creep," but there is little 

 doubt that its rate is overmatched by that of subserial erosion. 

 Where, however, such shales are continued across a valley-bottom, 

 and whether covered or not along that interval, provided (as, 

 indeed, in the nature of things can only be the case) the superior 

 strata are thicker and therefore heavier beyond the valley sides, 

 the pressing-out force will be unequally exerted, being strongest 

 where the weight above is heaviest. Hence it is plain that these 



