74 M. Oil. Martins on the 



erratic blocks, and furrowed with rectilinear strias, often 

 many metres in length. Without leaving the great road, 

 we may see one of those hills on the left bank of the Arve, 

 after passing the bridge Pelissier ; it is that on which the 

 picturesque ruins of the tower of St Michael stands. Every- 

 where around these hills we find blocks of protogine cover- 

 ing polished and striated rocks. These blocks are often as 

 it were suspended on the sides of the hill, in such positions 

 that we are inevitably led to the conclusion that they have 

 been transported by an agent whicli has deposited them 

 gently and without shock in the place where they have re- 

 mained in equilibrio, whereas an impetuous torrent would 

 have hurried them along and precipitated them into the 

 bottom of the valley. 



What were the dimensions — the puissance — of the glacier 

 when it made its way through the defile of the Montees I 

 In order to answer this interesting question, I ascended the 

 two banks of the Arve ; on the right, above the rocks whoso 

 precipitous walls ran into the torrent, I found polished rocks 

 and erratic blocks, at a height of 758 metres above the bridge 

 Pelissier. On the left, not far from the Col de la Forclaz, 

 the blocks rose to the height of 683 metres. These two 

 points, situate opposite each other, are separated by a hori- 

 zontal distance of at least 4 kilometres. The glacier was 

 therefore a league broad at this point, and its medium di- 

 mensions were 720 metres (2215 French feet) at least ; for, 

 in measurements of this kind, one can never be certain that 

 they have suspended the barometer precisely above the last 

 polished rock, or near the last erratic block.* 



Beyond the village of Servoz, the traces of the glacier of 

 the Arve (it is by this name we shall henceforth distinguish 

 it) disappear for some space. We pass over immense eboule- 

 ments which have buried the moutonned rocks and the blocks 

 of the moraine under a thick bed of debris. One of these 

 eboulements, in 1751, was accompanied with such a terrible 

 noise, and so dark a cloud of dust, that the authorities of the 



* This thickness need not excite surprise, when we consider that that of the 

 present glacier of the Aar near Absehwung is about 400 metres. 



