Yol. 52.] DEPOSITS, ETC., IN SUBALPINE SWITZERLAND. 585 



was an unbroken period of erosion and denudation on a prodigious 

 scale. The long duration of this post-Miocene and pre-Glacial 

 period appears the more obvious when we reflect that it was 

 contemporaneous with the formation of the extensive marine beds 

 of the Subapennine hills and of Sicily. 



It is a singular fact that the geological epoch which immediately 

 preceded the appearance of man is perhaps the most difficult to 

 unravel. But unless we assume that in this post-Miocene and 

 pre-Glacial period, which Sir Charles Lyell regarded as of incal- 

 culable duration, 1 the work of Nature stood still, we are driven to 

 the conclusion that, at the advent of the first Ice-period in Upper 

 Pliocene times, the principal Subalpine valleys were already ex- 

 cavated approximately to their present depth, aud that ever since 

 then the action of the great Alpine and Subalpine rivers has been, 

 as it still is in our own day, mainly directed to regaining the old 

 valley-floors by removing those enormous accumulations of glacial 

 and glacio-fluviatile material which are respectively the direct and 

 indirect products of three successive and general glaciations. 



Discussion. 



Prof. Bonnet said that he had been shown some of the sections 

 described by Dr. Preller, and could answer for the relations of the 

 various gravels and moraines. He felt some doubts as to the 

 occurrence of ' Deckenschotter ' by the side of the Limmat below 

 Baden. He felt the greatest difficulty of all in understanding how 

 the Deckenschotter was deposited on the Uetliberg and yet could 

 occur by the Lake, for that meant a difference of at least 1200 feet, 

 and he saw no way of explaining this. Was the valley filled up with 

 loose debris, or had it been deepened ? Which hypothesis offered 

 the less difficulty ? 



The Rev. Edwin Hill spoke of the great interest of the subject, 

 especially the singular alterations in the courses of rivers. Like 

 moraine-formed tarns, we had now shown to us moraine-diverted 

 rivers. 



Dr. G-. J. Hisde enquired of the Author if there were any 

 palaeontological grounds for attributing a Pliocene age to the plateau 

 fluvio-glacial gravels or ' Deckenschotter.' The well-known fact of 

 the similarity of the constituents of the gravels and conglomerates, 

 both of those of the plateau and of the high and low terraces, must 

 make discrimination difficult ; and he doubted the value of the 

 evidence relied on by the Author to prove that certain gravels and 

 conglomerates close to Zurich and nearly at the level of the Lake 

 belonged to the same period as the ' Deckenschotter ' at the top of 

 the Uetliberg, nearly 1500 feet higher. 



The Author thanked the various speakers for their remarks. In 



1 'Antiquity of Man,' 1863, p. 316. Sir Charles Lyell speaks of the 

 'countless post-Miocene ages which preceded the Glacial Epoch,' and in which 

 'there was ample time for the slow erosion by water of all the principal 

 hydrographical basins of the Alps.' 



