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GEOLOGICAL MEMOIRS. 



tudinal axis of the Alps from west to east. Under no other circum- 

 stances can we most easily perceive that the Alps are composed of a 

 series of " groups " [Gruppen, massifs], and not of parallel lines. The 

 long valleys enclose these " groups," and hence take very various 

 directions. We find them, therefore, stretching sometimes from north 

 to south, as the two arms of the Etsch Valley, and many others. 



They are for the most part reducible to two divisions. The one set 

 are characterized by a stronger inclination and by the alternation of 

 great flat basins with dells, often very long and narrow, and, as in 

 the cross-valleys, having a greater fall than that of the basins. The 

 upper extremity of the valleys varies considerably. They may, in- 

 deed, as in the transverse valleys, take their rise on high crests ; 

 generally, however, this is not the case. These longitudinal valleys 

 must on the whole be considered as deep depressions around the 

 lofty mountain groups. Their upper extremities, therefore, lie for 

 the most part deeper than those of the transverse valleys. The water- 

 shed between two long valleys is sometimes formed by a broad tract, 

 which is enclosed by high mountains and slopes gently on two oppo- 

 site sides, as is so clearly the case in the Pusterthal or on the Brenner. 

 Sometimes, however, the two sides have very different inclinations ; 

 this happens especially with those branches that pass to the south, 

 since the fall is here always more considerable. A fine example of 

 this occurs in the valley of the Inn, the unusually broad plateau of 

 which, at the Maloja Pass, descends towards the south with steep 

 precipices. 



Longitudinal valleys of the second division commence as soon as 

 they descend to a certain height and pass as broad depressions between 

 parallel mountain-chains, which very often belong to different geo- 

 logical formations. The fall then becomes trifling ; the valley -bottoms 

 are filled with beds of gravel ; they are always broad, and often of 

 great longitudinal extent, and are almost entirely free from any altera- 

 tion of its character, there being a discontinuance of the basins and 

 terrace-like sinkings. The direction of the valley also is less subject 

 to variation. When, however, the direction is changed, ravines, or 

 narrow passes, " Klausen," often occur which are overlooked by an- 

 cient fortifications, and have attained historic celebrity; in these 

 cases the longitudinal valleys form the most important roads through 

 the Alps. Such narrow passes are frequently found when the valleys 

 leave the Alpine districts and descend towards the northern or southern 

 plains, as in the case of the Porta Westphalica. In comparing the 

 longitudinal and the transverse valleys, we find that the mean inclina- 

 tion of the former is less, both on the whole and at particular parts. 

 The basins of the former are larger and more level, their valley- 

 bottoms broader, and their upper ends attain by no means such an 

 absolute altitude as those of the latter. In both, however, the mean 

 inclination increases in the highest portion and is greatest in the 

 ravines (intervening dells). * 



Secondary transverse Valleys. — Besides the long- and the cross- 

 valleys, before-mentioned, there is an extensive series of smaller val- 

 leys. Their proportion to the former appears also to be important, 



