INTERGLACIAL EPOCHS. 301 



Yet another example to show that there have been more 

 than one great invasion of the low grounds of Switzerland by ice. 

 At the Bois de la Batie above the confluence of the Arve with the 

 Bhone, near Geneva, thick boulder- clay is seen resting upon 

 conglomerate or hardened river-gravel. This latter bed is, 

 unquestionably, the ancient alluvium of the Bhone. Is it, then, 

 preglacial ? Its contents shall answer for us. Here are a 

 number of stones which could only have been derived from the 

 upper valley of the Bhone, such as the euphotide from the 

 valley of Saas, in Valais. It is quite impossible that the Bhone 

 could have carried them into their present position, for the deep 

 cavity of Lake Leman (334 metres) intervenes. We must per- 

 force agree with M. Tardy, who remarks, that " a glacier is in fact 

 the only vehicle which could have transported them across the 

 lake from their parent rocks in Valais." And that this glacier 

 was not the same as that which buried the ancient alluvium 

 underneath its boulder-clay is proved by the fact, mentioned by 

 Brofessor Favre, that the ancient river-gravel, at the time of the 

 last advance of the glaciers, had already been cemented into a 

 hard conglomerate, and was striated and polished just like any 

 other indurated rock-mass. Not only so, but it had been cut 

 down and highly denuded and worn into terraces by running- 

 water long before the last great mer de glace overflowed it. It 

 is further worthy of note that the ancient river-gravel rests upon 

 marly clay with freshwater-shells and traces of plants. These 

 facts show us that before the formation of the ancient gravel and 

 its associated deposits, the Bhone glacier must have filled up the 

 basin of the lake and strewed the ground at its lower end with 

 morainic detritus derived from Valais. Then came a period 

 when the glacier disappeared and its morainic deposits were 

 waterworn and re-arranged, and distributed over a wide area in 

 the neighbourhood of Geneva. In later ages the ancient allu- 

 vium was denuded and trenched by the streams cutting their 



under boulder-deposits in Switzerland, see Zeitschr. dcutsch. geol. Oes., 1880, p. 

 84, where Professor Credner describes and figures certain sections which were 

 observed many years ago by Escher von der Linth and A. Heim. 



