FORMER EXTENSION OF THE ALPINE GLACIERS. 359 



fied, and this material forms as a whole fan-shaped detrital piles at the 

 points where the various streams debouch from the mountain vallevs. 

 The contrast between these deposits and those left along the flanks of a 

 range by undoubted glaciers, as, for instance, at the base of the Sawatch 

 Range, in the Rocky Mountains,* is most striking. In the latter case we 

 have great accumulations of almost exclusively angular debris heaped up in 

 two well-marked parallel lines along the sides of the now much diminished 

 streams, and at right-angles to the trend of the range ; at the base of the 

 Bavarian Alps, on the other hand, we find water-worn detrital materials 

 forming a belt of irregular width along the whole extent of the range, but 

 spreading to considerably farther towards the north and occupying a fan- 

 shaped area in front of the mouths of the gorges from which the principal 

 streams now issue. Moreover, tliese deposits of lounded gravel are generally 

 quite distinctly stratified ; and if they are of morainic origin their whole 

 mass must have been entirely worked over and rearranged by water after 

 having been deposited by the glacier. 



The views of Stark are on the whole adopted and supported by Zittel, 

 who, however, does not hesitate to call to aid a pre-glacial period of floods 

 in order to account for what he calls the " stratified diluvial gravel " [ge- 

 schichtetes Diluvialgerbll]. He says : " I consider it proved that, over the 

 Bavarian high plateau [Hochebene], the Glacial epoch was preceded by a 

 period of violent overflow or deluges [heftige Uberfluthungen], during which 

 enormous masses of detrital material filled up the depressions in the Tertiary 

 land, in which valleys had been previously eroded, so that a level base [Un- 

 tergrund] was prepared on which the glaciers which were to come later 

 might rest"! Thus, as we perceive, Zittel does, in foct, recognize the 

 necessity of admitting that there was a time in geological history when the 

 precipitation was much larger than it now is. This more copious rain-fall 

 he seems, however, to wish to limit to a certain comparatively brief period 

 previous to the Glacial epoch ; while so many other geologists, especially in 

 this country ,$ look upon tliis time when water was a mucli more active geo- 

 logical agent than it now is as a phase following instead of preceding the 

 epoch of the greatest ice extension. The subject of tlie extension of the ice 

 sheet on the north slope of the Bavarian Alps has been insisted on, in the 



* See ante, pp. 64, 65. 



+ See Zittel, in Sitzungsberichte der math. -pli3-s. C'lasse der k. b. .\kademie der Wissenschafteu zu Muucheii, 

 1874, p. 282. 



X See ante, pp. 184-193. 



