OF PHYSICAL GEOGRAPHY. 11 



And different from either are the rounded knolls of the shale 

 which occur in the country of Ribblesdale. 



The combination of these forms into groups occasions quite 

 different pictorial effects. Compare, for example, the scene from 

 the Buttertubs Pass between Muker and Hawes (PL IV.), in 

 which alternating limestones and gritstones give the most pro- 

 minent effects, with contours of the Craven district near Skipton 

 (PI. III. fig. 1), the bold edges being made of thick gritstone 

 (g), and the lower swelling hills of shale (s). 



Or contrast the abrupt outlines, such as those of Oliver's 

 Mount and the Nabs near Scarborough (PI. III. fig. 3, n), with 

 the easy and flowing curves which everywhere mark the edges 

 of the chalk wolds (w). 



In the former case a hard rock, calcareous grit, guards the 

 brow, and the slope below is clay, alternating with easily disin- 

 tegrated sandstone ; in the latter case, the chalk in great thick- 

 ness and full of small fissures, yields rather easily to degradation, 

 and nowhere preserves abruptness of parts, however bold may 

 be the general effect. 



The great inland cliffs, which are among the most striking 

 phenomena of Yorkshire, only differ from sea cliffs, because 

 the water no longer beats against them. The Hambleton hills, 

 the Wolds, no less than Giggleswick Scar, were cliffs against a 

 wide sea. Kilnsey Crag was a promontory overhanging the 

 primaeval loch, which is now the green valley of the Wharfe; 

 and the mural precipices which gird the bases of Whernside, 

 Ingleborough and Penyghent, formed bold margins to similar 

 branches of the sea, which extended up Chapeldale and Rib- 

 blesdale. 



The softer strata are more worn away on the slopes of hills 

 than the harder rocks, and for that reason appear in concave 

 surfaces there; for the same reason valleys are often widened 

 into expanded hollows in these strata, and contracted between 

 cliffs where the sides are formed of firmer materials. For the 

 same reason, on the sea-coast, the far extended promontories 



