66 



VALLEYS. 



action of water or some convulsion, which has torn 

 off and carried away the strata by which they were 

 once covered.* Tliis, therefore, is cailed a denuda- 

 tion ; and such instances are of frequent occur- 

 rence. 



When valleys take the same direction asjhat of 

 a range of mountains, they are called longitudinal 

 valleys; when tljey cut through a range of mount- 

 ains, they are called transversal valleys ; in which 

 case the strata on each side are generally the 

 same. Small valleys, which open into a larger val- 

 ley nearly at right angles to it, are called lateral 

 valleys. Sometimes a valley is formed by the bend- 

 ing of the strata, thus : 



Fig. 22. 



Bakewell remarks, that the beds or strata of very 

 lofty mountains are generally much inclined, and 

 are sometimes nearly vertical. Among these high- 

 ly-inclined beds we not unfrequently find beds of 

 limestone, containing marine shells which must 

 have been originally deposited at the bottom of the 

 ocean. In some instances we meet with vertical 

 strata, containing rounded pebbles and water-worn 

 fragments of other rocks. These must also have 

 been originally deposited on a surface nearly hori- 

 zontal. We are therefore certain that the present 

 vertical position of these strata is not their original 

 one ; and we hence also learn, that all the strata 

 associated with them in the same mountain, and 

 having the same inclination, were raised together. 

 We have farther proof that, before the epoch when 

 this great revolution was effected, all these beds 

 were covered by seas then existing, and that it was 



* Bake well's Geology. 



