2 9^ Hints for the Formation of 



of the valley, which would indicate that the valley has been 

 produced by a finking down of the earth, or perhaps by the 

 oppofite faces being thrown up. 



11. There are two other cafes pofilble when the ftrata 

 have not the fame fltuation on both fides of the valley. 

 J. When the firata rife up on each fide againft the valle\ . 

 2. When on one fide they defcend into the valley, and on 

 the other rife againft it. ■ Thefe two cafes afford room for 

 iuppofitions too various to be here detailed. 



1 2 . To fearch on the vertical fides of the valleys for vef- 

 tiges of the erofion of the water. 



13. To obferve the bottom of the vallcv, its breadth, in- 

 clination and nature. The vegetable earth, its quantity 

 and quality; fragments, cither from neighbouring moun- 

 tains, or brought from a diflance, either angular or rounded; 

 to examine whether they arc more voluminous towards the 

 top of the valley. Nature and depth of the ftrata which are 

 below the vegetable earth ; whether the pebbles are larger 

 in the dcepeft ftrata: nature of the rock which forms the 

 folic! bafis of the valley. 



14. Whether a \ alley contains foreign pebbles, that is to 

 fay, which come from the neighbouring mountains : to exa- 

 mine to what height they are found on the fides of the 

 mountains ; what may be their origin, and what way they 

 mav have been conveyed. 



.15. In the valleys which contain no foreign pebbles, one 

 may follow the traces of thofe which are there difcovered, 

 and thus afcend to the rock from which they were detached : 

 this has often led to curious and ufeful difeoveries. 



CHAP. XIII. 



(jhfcrvat'wns to be made on Tertiary Mountains, or thofe com^ 

 pofed, of the Wreck of other Mountains. 



t. Whether they do n,ot form the external border of other 

 chains of mountains, 

 %, Whether, at the extremity of great valleys which ifiue 



from 



