454 Uniform Contours (with variable materials) of Hills. 



Now these pieces of rock remain in the stream, and protect the underlying 

 beds. With torrents flowing, protecting rocks would be carried down, and valleys 

 excavated with the greatest rapidity. Our hills were shaped by the same process. 

 Fig. 2 IE represents a hill of glacial drift drawn by Erdmann. It is evident 

 that the disposition of the internal strata does not materially affect the contour. 

 From page 57 Formations de la Suede. 



24. a . Coarse Gravel, 

 b .Sand. 



c . Fine sand. F!G:2I.E 



d. do „ do„u/iih elaif. 

 I . Glacial clay. 



j 100 feet 



Fig. 2 ID. Sketch of outline of sandhills, near Leighton Buzzard, Beds. 



Crowborough Beacon, in Sussex, only remains as a high hill in consequence 

 of the ironstone in the sands of which the hill is composed, paving the 

 brooks and keeping the water from touching the sand below. Ecclesbourn 

 Glen (Fig. 24) is a good and accessible instance. The pieces of fallen rock 

 pave the channel so as to resist 4 the denuding action of the stream. 



SECTION. 

 through, Jl.D. 



Watershed. 

 A. 



f/g: »s 



fic: 2lfe 

 S ECTION fhvoutjh EE 



4 '.J JZO 210 2S2. 21Q JSO as JO 



FJC2I.D 



Ximmeridge Clay 



* A.7YLOR.DEL. 



Fig. 23, p. 456, is a section through the waterfall Fig. 24 showing the bed of 

 clay underneath the hard rock: water oozing through the joints of the stone passes 

 between the stone A and the clay B. As the edge of clay at C is washed down, 

 the stone at A falls there. This is the same case as Niagara, where a thick 

 rock breaks vertically through the water from the lake above, passing below 

 the Niagara rock and removing the base of shale. 



(25) Fig. 24A gives a view of the Chalk hills near Folkestone, where small 

 lateral valleys have been cut out by rivers flowing out of springs in the pluvial 

 period. They are almost dry now, but were once of immense volume. 



