TWO GLACIAL EPOCHS. 201 



mcrous alternations of temperature. No "regularly continued 

 transition appears to have occurred ; but a cold period separated 

 the lignite formation from the Miocene. 



Two glacial epochs arc indicated by the mode of dispersion of 

 the boulders in the basin of the Rhone. The second of these 

 epochs corresponds with the later condition of the Ehone glacier, 

 when, it had been melted back as far as the basin of the lake of 

 Geneva. Prof. Morlot * has shown it to be very probable that 

 formerly the Rhone glacier retreated not only into the region of 

 the Lake of Geneva, but also to the main valley of the Canton 

 of the Valais (he supposes, to an elevation of from 30004000 

 feet above the sea), and that again the glacier advanced, but in 

 the second period merely spread itself over the basin of the 

 Lake of Geneva. According to this view there were two glacial 

 epochs, separated by a period during which the glaciers dis- 

 appeared from all the plains of Switzerland. In the second 

 Glacial epoch the streams flowing from the hills near the Lake 

 of Geneva mingled their debris with those of the lateral mo- 

 raines ; and thus the deposits were formed which produce a line 

 of terraces along the lake, and which here and there show strati- 

 fication and contain numerous scratched and angular erratics, 

 thus resembling the deposits sometimes found on the existing 

 glaciers at points where lateral brooks flow towards them and 

 form small lakes and pools, which are gradually filled up by 

 the moraines. 



Prof. Morlot found the principal evidence in favour of these 

 two glacial periods in the ravine of the Dranse, near Thonon. 

 At the bottom of the gorge there is (1) a deposit of debris 

 12 feet thick with striated fragments of Alpine limestone ; and 

 above this is (2) a bed of rolled and stratified pebbles (drift), 

 150 feet thick; and, again, above this bed are (3) striated 

 erratic blocks. Between the formation of the first and third of 

 these deposits, which were produced by a moraine, intervened 



* "Note sur la subdivision du Terrain Quaternaire en Suisse," par A. 

 Morlot (Bibl. Univ. 1855). According to Scipio Gras, two glacial deposits 

 are to be distinguished in the Lower-Rhone basin. See his memoir " Sur la 

 periode Quateriinirc dans la vallee du Rhone, et sa division en cinq epoques 

 distinctes" (Hull. Soc. Geol. France, xix., Nov., Dec.). 



