368 Analyses of Books. [Nov. 



they were removed from those parts at present constituting the 

 valleys. 



Another evidence that this has been the origin of valleys is, 

 that when a vein or a dyke passes through a rock, it is not cut 

 off by a valley, but appears again in the rock on the other side of 

 the valley : indicating that at first it passed without interrup- 

 tion through the strata which formerly filled up the valley before 

 it was excavated. 



We can very frequently observe the same coincidence in the 

 nature of the soil, gravel, and bowlderstones, on the opposite 

 sides of a valley. 



It is true that the coincidences here pointed out are not 

 always to be observed, and Deluc made use of this want of 

 universal coincidence as an objection to the doctrine that valleys 

 owe their existence to excavation. But our author considers 

 Deluc's objection as of no force, because valleys often run along 

 the line of the junction of two different rocks, and in such cases 

 a coincidence cannot be looked for. 



Our author further observes, in corroboration of his opinion, 

 that we often observe a correspondence in the position of strata 

 on the opposite sides of valleys. This correspondence in dip 

 does not indeed prove that strata have been united, provided we 

 find a different dip in the intervening space ; but when two 

 opposite cliffs correspond in every respect, we can entertain no 

 reasonable doubts that they once were united. 



Bowlderstones, so abundant on the north side of the Alps, 

 and on the south side of the Baltic, further evince the excava- 

 tion of valleys. They may be often traced to the place whence 

 they came. Of this, our author gives many examples. Thus 

 the blocks of granite in Cheshire, Staffordshire, Shropshire, &c. 

 may be traced to the Cambrian mountains. I may add another 

 example which I believ r e to be rather uncommon. The merse, 

 or low part, of Berwickshire, contains many bowlders of a 

 greenstone distinguished by large crystals of greenish-white 

 felspar. These bowlders may be traced to the cheviots which 

 lie at a considerable distance to the south-west. 



Another proof that valleys have been excavated, and that they 

 have been excavated by water, is, that very frequently the oppo- 

 site projections and indentations of the bounding mountains 

 correspond. This fact was first noticed by Bourguet in 1729 ; 

 but did not attract much attention till illustrated by the eloquence 

 of Buffon. Humboldt, when he says that this agreement may be 

 observed on the opposite coasts of the Atlantic, in the opposite 

 projections and indentations of the old and new continents, has 

 extended the doctrine too far. We can conceive no flow of 

 water of such magnitude as to be capable of excavating the 

 Atlantic and indenting the sides of the opposite continents. 

 Such generalizations are too vague to be of any utility, and can 

 serve no other purpose but to mislead. 



