Secondary Rocks. 43 



tions. It is superfluous, with a view to the preliminary infor- 

 mation necessary for the investigation of a separate part of a 

 mountainous tract, to go into greater detail, and it only re- 

 mains for us to mention shortly some particulars respecting the 

 characters of such pieces of country as form the separating 

 boundaries of different mountain-tracts, at least in their longi- 

 tudinal limits. 



***** 

 Characters of such pieces of country as form the boundaries of 

 different Mountain-tracts.— -It is generally a difficult matter to 

 define with precision where a mountain-group ends and the 

 bounding plains begin. The rocky masses which constitute the 

 one and the others, often seem to be connected in such a man- 

 ner, that even in their phenomena of superposition, no striking 

 or fixed determinable distinction exists ; but on the contrary, 

 the latter follow the former with almost the same features of 

 arrangement, although generally with a smaller inclination ; and 

 the superficial relations are so gradually changed, that, not- 

 withstanding their great difference, they pass as it were imper- 

 ceptibly into each other. Sometimes, however, these relations 

 are quite of another description. There is not only an inter- 

 ruption as it were in the sequence of the rocky masses, inas- 

 much as there are certain masses awanting between those 

 that are present, but there are likewise altered relations of 

 superposition, of such a nature that the mountain-masses of 

 the plains which are uniformly arranged in respect to one 

 another, appear in a certain discordant arrangement as re- 

 gards the equally uniformly arranged masses of the moun- 

 tains, and the superficial relations are suddenly altered in 

 such a manner, that soft low districts, only traversed by flat 

 elevations, are contiguous to tracts which are precipitous and 

 lofty, and not unfrequently include naked recks, just as the sea 

 borders on abruptly rising cliffs. But this determination of 

 boundaries, as well as the more detailed account and explana- 

 tion of the difference of the relations on the our and the other 

 side of the limit, which perhaps is greater than at first sight 

 appears, may reasonably be passed over here, as they only relate 

 to a series of mountain-masses, \i/.. wbal are termed the 



