326 Pi^of. Striide?- on Bowlders. 



the interior of Switzerland, had only a very small depth and al- 

 ternated with dry land such as we now regard as low land, (tief 

 land) ; and, finally, that the elevation of the Alpine chain could 

 scarcely have been an instantaneous thrusting up of the whole 

 mountain mass, in which the sea might have been slung on 

 high with it, but a very complicated process continued through a 

 long space of time.* The great depth of the Swiss lakes has 

 ever been the principal objection with the opponents of that ex- 

 planation, and the ease with which the new ice and glacier theory 

 sets aside this difficulty, accounts of itself for the interest with 

 which it has been received. The difficulty lies not, as I think, 

 in carrying the detritous streams and blocks over the lakes. 

 The water-course could do no more than force a part of the wa- 

 ter of the lake, and, considering the small difference of specific 

 gravity, the height and rapidity of the streams, hardly a very 

 important part, out of its basin and mingle with it ; had the 

 stream at once poured itself out entirely over the whole lake, in 

 that case the back portion of the detritus would flow on over it, 

 as we see the upper water in our lake move over the deep, still 

 water. The separation of the solid materials from the detritous 

 water might to be sure raise the bottom of the lake, yet not 

 more than we see the bottom of the molasse-vallies now elevated 

 in many places by diluvial ruins, that is, at the highest one hun- 

 dred feet. Nor is it difficult of solution why the basins of the 

 lakes have not been entirely filled up by the later transportation 

 of smaller blocks such as have occurred in part within the his- 

 torical period ; for, originally these blocks were not, as is gene- 

 rally supposed, so naked and free, as we now see them, but cov- 

 ered with thick coatings of rubbish. This appears very clearly, 

 among other examples, in the immediate neighborhood of Berne. 

 A row of low hills stretches in an arch convex to the west across 

 the Aar-valley close to the west end of our city, which has used 

 its contiguous eminences for breast-works. In the late demoli- 

 tion of the fortifications, these eminences which were universally 

 supposed to be works of ai't thrown up on the common level of 

 the ground, were penetrated to their center and it was found that 

 they consisted for the most part of enormous heaps of Alpine 



* The imbedding among the diluvial ruins of the blocks at Str^tligen and Utz- 

 nach, of unchanged pines and firs, plants and insects of the present time in brown 

 coal, appears to place the spread of this detritus at a very recent epoch. 



