Ancient Extent of the Glaciers of Chamonix . 75 



neighbouring town sent a courier to Turin to announce 

 that a volcano had broken out among the Alps. 



On the left bank of the Arve, the marks of the ancient 

 glacier have not been concealed as on the right bank. If wq 

 follow the road which leads from the village of Chede to the 

 baths of St Gervais, we agam find blocks of protogine on the 

 sides of tlie torrent, at the outlet of the narrow gorge 

 through which it escapes to enter the valley of Sallenches. 

 One of these blocks is surmounted by a pigeon-house, which 

 attracts the attention of travellers from a distance. 



The baths of St Gervaise are situate at the extremity of 

 the valley of Montjoie, which runs along the western side 

 of Mont Blanc, and cuts that of the Arve almost at a right 

 angle. The torrent Bonnaut, which forms behind the baths 

 ft cascade celebrated among tourists, runs in the bottom of 

 the valley. If the theory of the ancient extension of glaciers 

 is not a vain hypothesis, the valley of Montjoie ought, like 

 that of Chamonix, to send forth a glacier, and at its point of 

 meeting with that of the Arve, we ought to recognise traces 

 of the appearances which are observed in existing glaciers 

 at the junction of two affluents. If these affluents are of 

 equal force, they unite and advance in a parallel direction 

 side by side ; but, if they are of unequal size, the smaller is 

 forced aside by the larger, and forms only a kind of wedge 

 which penetrates more or less into the principal glacier. 

 The union of the glaciers of Lauteraar and Finstcraar, is 

 an example of a confluence of the former kind ; the small 

 glaciers of Thierberg, Silberberg, and Griinberg, which throw 

 themselves into that of the Aar, shew us what takes place , 

 in the second instance. Compared with that of the Arve, 

 the glacier of Bonnaut was but a weak tributary ; however 

 it has deposited its blocks at the entry of the valley of Mont- 

 joie, where, over a space of some kilometres, they alone cover 

 the sides of the mountain between St Gervais and Com- 

 bloux ; but at the same time the glacier of Bonnaut, driving 

 back the lateral moraine of the glacier of the Arve to the 

 middle of the valley, has forced the blocks of protogine to 

 recede from its edge. Accordingly, when the glacier of the 

 Arve melted, these blocks, instead of remaining suspended 



