IL' PRINCIPAL FEATURES 



are composed of more solid rocky masses than the bays on either 

 side. Thus Flamborough Head, a mass of rather firm chalk, 

 projects between the sands, clays and gravels of Holderness, and 

 the clays of Filey Bay ; the calcareous ledges of Filey Brig in 

 like manner stretch out into the sea, between bays of softer 

 matter ; Scarborough Castle Hill is a third example. (See the 

 Geological Map.) 



Looking specially to the action of water now running in the 

 valleys, we observe that the very channel is marked by peculiari- 

 ties of the same kind, and depending on the same conditions. 

 To instance only the most beautiful of the peculiarities of our 

 northern rivers, the * forces ' and rapids, which impart so much 

 interest to the Valley of the Yore. In accompanying many little 

 streams which descend from the moors, several hundred feet 

 before they reach the river, we find at almost every point where 

 limestone beds rest upon shale, and often where sandstone beds 

 take the similar position, a step in the channel, over which the 

 water falls a few inches, a few feet, or many yards, according to 

 circumstances. Each of these little cascades is subject to dis- 

 placement. The limestone beds are slightly worn away and 

 excavated by the sharp sands and pebbles which the stream 

 brings downwards, but this is a feeble element of change. A 

 more powerful effect is occasioned when the rock is undermined 

 by the more rapid waste of the shale, and it consequently breaks 

 off at one of the numerous natural joints, and falls. Thus the 

 operation by which Niagara has been removed, and is under- 

 going removal, which has furnished to Sir C. Lyell most interest- 

 ing reflections, may be witnessed on hundreds of streams in 

 Yorkshire. The scale is microscopic, indeed, but its results 

 are of the same order, fully as instructive and not less impress- 

 ive on the mind. 



The mere action of the humid and variable atmosphere of 

 England, is wasting, every hour, the surfaces of what are vainly 

 thought to be eternal hills. Even the drop of rain cannot be 

 traced from the cloud, over the surface and through the sub- 



