Observations on Glaciers. 7 



I feel certain, could not take place were the sliding theory 

 true. 



But if possible, still stronger, as well as more multiplied, 

 objections are to be found to the theory of dilatation, and I 

 trust I shall not be accused of levity in thus, as it were, in a 

 few lines, dismissing a theory which has so much jmrnu facie 

 plausibility to recommend it, and which has been maintained 

 with so much ingenuity by men such as Scheuchzer, De Char- 

 pentier, and Agassiz. It is essential to the aim of this letter, 

 that I state briefly the grounds of the conclusions at which I 

 have arrived, whilst it is equally essential that my observa- 

 tions should be confined within small compass. In another 

 place I shall give them all the development that may be re- 

 quisite. 



Summarily, then (l.)The motion of the glacier, in its several 

 parts, does not appear to follow the law which the dilatation 

 theory would require. It has been shewn (Ed. Rev., April 1842, 

 p. 77.) that the motion ought to vanish near the origin of the 

 glacier, and increase continually towards its lower extremity. 

 I have found the motion of the higher part of the Mer de Glace 

 to differ sometimes very little from that several leagues far- 

 ther dowTi ; whilst in the middle, owing to the expansion of 

 the glacier in breadth, its march was slower than in either of 

 the other parts. (2.) Whilst I admit that the glacier is, dur- 

 ing summer, infiltrated Avith water in all or most of its thick- 

 ness (a point on which I had last year great doubts), 1 feel 

 quite confident that, during some months of the year during 

 which the glacier is in most rapid motion, no congelation takes 

 place in the mass of the ice beyond a depth of a very few 

 inches, much less dui'ing the cold of each night, and least of 

 all, at all times, as appears to be now the opinion held upon 

 the subject. Whilst I say that I am confident of this, I will 

 state one proof. Less than ten days since I traversed the Mer 

 de Glace up to the higher part of the Glacier de Lechaud, 

 whilst it was covered with snow to a depth of six inches at 

 Montanvert, and three times as much in the higher part. It 

 was snowing at the time, and for a week the glacier had been 

 in the same state nearly, the thermometer having fallen in the 

 mean while to 20^ Fahr. Yet I had abundant evidence that 



