316 THEORY OF THE ORIGIN OF LAKE-BASINS CHAP. xv. 



embedded trunks of pines of the same species drifted down 

 during freshets. Such deposits would be most frequent at 

 the upper ends of the lakes, but a few would occur on either 

 bank not far from the shore, where torrents once entered, 

 agreeing in geographical position with the lignite formations 

 of Utznach and Diirnten. 



There are other freshwater formations with lignite, besides 

 those on the lake of Zurich, as those of Wetzikon, near the 

 Pfaffikon Lake, of Kaltbrunnen, of Buchberg, and that of 

 Morschweil between St. Grail and Rorschach, but none pro 

 bably older than the Diirnten beds. Like the buried forest 

 of Cromer (p. 214), they are all pre-glacial, yet they by 

 no means represent the older nor even the newer pliocene 

 period, but rather the beginning of the post-pliocene. It is 

 therefore true, as Professor Ramsay remarks, that, as yet, no 

 strata c of the age of the English Crag' have been detected in 

 any Alpine valley. In other words, there are no freshwater 

 formations yet known corresponding in date to the pliocene 

 beds of the upper Val d'Arno, above Florence a fact from 

 which we may infer (though with diffidence, as the inference 

 is based on negative evidence), that, although the great 

 Alpine valleys were eroded in pliocene times, the lake-basins 

 were, nevertheless, of post-pliocene date some of them 

 formed before, others during, the glacial epoch. 



6th] y. In what manner, then, did the great lake basins ori 

 ginate if they were not hollowed out by ice ? My answer is, 

 they are all due to unequal movements of upheaval and sub 

 sidence. We have already seen that the buried forest of 

 Cromer, which, by its organic contents, seems clearly to be 

 of the same age as the lignite of Diirnten, was pre-glacial, 

 and that it has undergone a great oscillation of level (about 

 500 feet in both directions, see p. 227) since its origin, 

 having first sunk to that extent below the sea, and then 

 been raised up again to the sea-level. In the countless post- 



