PRINCIPLES OF GEOLOGY. 21 



is certainly true, that the great mountain ranges which seem to compose 

 the skeleton of the earth ; the wide oceans, plains, and level tracts, and 

 even the remarkable lines of secondary hills and most extensive vallies, 

 are placed in accordance to the interior structure of the earth. Hence, it 

 follows that we must limit our inquiry, as to the changes produced on the 

 surface of the earth by the deluge, to the vallies and hills which seem 

 evidently to have derived their peculiar features from currents of water, 

 since the consolidation of the strata. Even thus limited, the subject is 

 ample, fertile, and instructive. Many vallies in a secondary country are 

 excavated through several strata, as limestone, clay, and sandstone, which 

 appear on the opposite sides in most exact agreement as to thickness, 

 composition, and mode of arrangement. That such rocks were originally 

 deposited in continued planes, and, therefore, once connected across the 

 chasm or valley which now divides them, can hardly be doubted. The 

 vallies themselves bear marks of their origin ; their bottom is a continued 

 plane ; their sides correspond with answering sinuosities ; and their every 

 peculiarity suggests the action of decurrent water. From the time of 

 Pythagoras to the present day, every unprejudiced observer of nature has 

 concluded that such vallies were cut out of the planes of the consolidated 

 strata, through one, two, or more rocks, according to the depth of the ex- 

 cavation, and in this or that direction, according to the facility with which 

 the materials were abraded. These are called vallies of denudation, and 

 they are very numerous and extensive. In western Yorkshire, the great 

 mining vallies of Teesdale, Swaledale, Yoredale, and Wharfdale, are mag- 

 nificent examples, and strongly impress the mind with the power of the 

 currents which occasioned them. In the eastern part of the county, 

 the vallies of the Derwent below Malton, Rievaulx and Bilsdale above 

 Helmsley, Newton Dale above Pickering, and Hackness near Scarbo- 

 rough, are remarkable and beautiful instances. 



There is one circumstance of common occurrence, which yields so 

 absolute a proof that vallies were formed at periods subsequent to the 

 deposition of the strata, and is in itself so curious, that though few will 

 seek more satisfactory evidence than in each case each valley furnishes, 

 it deserves to be mentioned. Some vallies cross and cut through vertical 



