OF PHYSICAL GEOGRAPHY. 15 



mites which are accumulated from the drippings of water along 

 fissures of the roof. This interesting cavern will claim more 

 detailed notice in another part of the work. 



From this very brief summary, we perceive that the main ex- 

 ternal features of Yorkshire are strictly explicable on the simplest 

 possible theory : viz. that of the long-continued action of the 

 agitated sea on the strata which composed its bed at the time 

 when this bed was raised to constitute land. These strata, by 

 their various degrees of consolidation and peculiarities of posi- 

 tion, offered unequal resistance to the waves, and have been 

 unequally wasted : the softer strata, which suffered most waste, 

 have left the greatest hollows : the red marls and blue lias 

 having been excavated in the Vale of York, the Kimmeridge 

 clays in the Vale of Pickering, the limestone shales in Craven, 

 and the tertiary sands in Holderness; while harder masses of 

 chalk constitute the Wolds, oolites and sandstones form the 

 moorlands of Whitby, still firmer sandstones and limestones, 

 with some slaty and some basaltic masses, constitute the higher 

 regions of the west. 



To geological differences on a large scale, we thus clearly trace 

 the main distinctive features of the great natural divisions of 

 Yorkshire. The mineral qualities and positions of rocks, with 

 the accidents to which they have been subjected, give us the 

 clue to the forms of mountains and valleys, the aspect of water- 

 falls and rocks, the prevalent herbage, and the agricultural appro- 

 priation. Even surface colour and pictorial effect are not fully 

 understood without geological inquiry. While limestone ' scars ' 

 support a sweet green turf, and slopes of shale give a stunted 

 growth of bluish sedge, gritstone ' edges ' are often deeply cover- 

 ed by brown heath, and abandoned to grouse, the sportsman, or 

 the peat-cutter. In a word, geological distinctions are nowhere 

 more boldly marked than in Yorkshire, or more constantly in 

 harmony with the other leading facts of physical geography. 



