THE EVOLUTION OF DERBYSHIRE SCENERY. 213 



isolated from the parent rock ? The answer which would glibly 

 be vouchsafed by the embryo student of Geology is, that the 

 action of the weather had carved out the spaces between the 

 hillocks, in the manner in which most other hills have been formed. 

 Such an answer would be found to be unsatisfactory, for it is found 

 that the appearances of the hillocks as regards contour and 

 verdure point to the fact that they are of different ages, the 

 grass-clad mounds near the brook being distinctly older than 

 those near the parent rock. An astute geologist would conclude 

 that these hillocks had slipped down from the parent rock over 

 the oleaginous shales which underlie them. Indeed, the ofificers 

 of the Geological Survey offer this explanation in the analogous 

 case of the peaked hillock known as Alport Tower, and the 

 surrounding hummocks. *7rMr. Ward is, however, of the opinion 

 that this explanation does not satisfy the facts of the case either 

 in the Alport instance or the one at Abney, and he suggests a 

 theory which is presented below. He argues that the isolation 

 of the hillocks cannot be due to slipping simply, for the detach- 

 ment of the masses has proceeded with some regularity, and 

 that such slipping could not have proceeded without considerable 

 disturbance of the bedding of the detached masses, which 

 certainly does not appear to has taken place. Further, the dip 

 is very gentle, not exceeding 3° to the north, which, in our 

 opinion, would not be competent to produce such slipping. 

 The explanation is to be found in the physical structure of 

 the underlying shales, which has been previously referred to. 

 Above these shales he a thickness of about 200 feet of shale 

 grit. So long as this superincumbent mass is continuous it 

 will be well supported by the shales below. But suppose, as 

 in the present case, that the cutting tools of nature carve 

 out a strip of this overlying plateau. Were there a con- 

 siderable amount of cohesion between the shales, no marked 

 effect would follow ; but, as has been pointed out before, the 



* Memoir of the Geological Survey : " The Geology of the Carboniferous 

 Limestone, Yoredale Rocks, and Millstone Grit of North Derbyshire," p. 42. 



