314 THEORY OF THE ORIGIN OF LAKE-BASINS chap. xv. 



according to the theory under consideration, in the sjiaco 

 now occupied by the moraine of the Dora Eiparia, between 

 Susa and Turin (see map, p. 306). vSignor Gastaldi has 

 shown that all the ponds in that area consist exclusively of 

 what M. de JVIortillet has denominated morainic lakes, 

 i.e. caused by barriers of glacier-mud and stones. 



5thly. In proof of the great lakes having had no existence 

 before the glacial period, Professor Eamsay observes that 

 Ave do not find in the Alps any fresh-water strata of an age 

 intermediate between 'Hhe close of the miocenic and the 

 commencement of the glacial epoch."* But although such 

 formations are scarce, they are by no means wholly wanting ; 

 and if it can be shown that any one of the i^rincipal lakes, 

 that of Zurich, for example, existed prior to the glacial era, it 

 will follow that in the Alps the erosive power of ice was not 

 required to produce lake-basins on a large scale. The depo- 

 sits alluded to on the borders of the Lake of Zurich are those 

 of Utznach and Diirnten, situated each about 350 feet above 

 the present level of the lake, and containing valuable beds 

 of lignite. 



The first of them, that of Utznach, is a delta formed at the 

 head of the ancient and once more extensive lake. The 

 artjillaceous and lio-nite-bearinji; strata, more than 100 feet in 

 thickness, rest unconformably on highly inclined and sometimes 

 vertical miocene molasse. These clays are covered conform- 

 ably by stratified sand and gravel sixty feet thick, partly con- 

 solidated, in which the pebbles are of rocks belonging to the 

 upper valleys of the Limmat and its tributaries, all of them 

 small and not glacially striated, and wholly without admix- 

 ture of large angular stones. On the top of all repose very 

 large erratic blocks, affording clear evidence that the colossal 

 glacier which once filled the valley of the Limmat covered 



■•■■ Geol. Quart. Journ., vol. xviii. 



