66 
VALLEYS. 
action of water or some convulsion, which has torn 
off and carried away the strata by which they were 
once covered.* This, therefore, is called a denuda- 
tion; and such instances are of frequent occur- 
rence. 
When valleys take the same direction as that of 
a range of mountains, they are called longitudinal 
valleys ; when they 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 
* BakewelPs Geology. 
