M. de Beaumont on (he Glacier Theory. 115 



In proposing this theoretical explanation of the formation 

 of ice in the interior of glaciers, and of the effects that result 

 from it, 1 by no means seek to dispute the conclusions in the 

 interesting memoir where Mr Hopkins has lately shewn the 

 feebleness of the theory which maintains that the sole cause 

 of the movement of glaciers is to be found in the effects of di- 

 latation. I may even add, in support of the arguments so well 

 developed by the learned Cambridge author, that if the expla- 

 nation now given be correct, it is only during a short period 

 (a few days or a few weeks) that glaciers augment internally, 

 and QO\\sc(\y\evLi\'^ di'ate each year. I am also convinced, by 

 many reasons which cannot be explained in this notice, that 

 the ithenomena of expansion are not the sole, or even the prin- 

 cipal cause, of the movement of glaciers, which, with tlieir 

 numerous crevasses, appear to me rather to resemble straps 

 QaJiieres) drawn downwards (as if by the action of a weight), 

 than bars which are compressed and pushed by a force pro- 

 ceeding from above (as would be the case on the supposition 

 of a force resulting from expansion). 



On the Slopes of the Upper Limit of the Erratic Zone, and on 

 their Comparison with the Slopes of Glaciers and of Biver- 

 Courses. 13y M. Elie de Beaumont, Member of the Royal 

 Academy of Sciences.* 



The interesting investigations of which the erratic pheno- 

 mena of tlie Alps have been for some years the oliject, have 

 contributed to demonstrate an im])ortant circumstance that 

 pervades the whole of tliis class of facts. The traces left by 

 the erratic phenomenon rarely extend to the summits of moun- 

 tains. They are concentrated in a zone which embraces their 

 base, and which has a well defined upper limit. This upper 

 limit is very frequently marked either by the passage of the 

 rounded rocks {roches moutonnees) into the angular rocks, or 

 by the highest terraces formed of erratic materials. 



In a district of small extent, the upper limit often seems to 

 bo indicated by a horizontal line, but this is an illusion caused 



* Rc.'id to tlic riiiloiniitliic So(icty on llio 13tli August 1842. 



