M. de Beaumont ott the 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, I by no means seek to dispute the conclusions m 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 w^ll 

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

 nation now given be correct, it is only during, a sho^i period 

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

 and consequently di'ate each year. I am also convinced by 

 many reasons which cannot be explained in this notice, that 

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

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

 numerous cremsses, appear to me rather to resemble straps 

 (lanih-es) 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 7vith the Slopes of Glaciers and of Fiver- 

 Courses. By M. Elie de Beaumont, Member of the Royal 

 Academy of Sciences.* 



The interesting investigations of which the erratic pheno- 

 mena of the Alps have been for some years the object, have 

 contributed to demonstrate an important circumstance that 

 pei'vades the whole of this class of facts. The traces left by 

 the erratic plienomenon 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 

 be indicated by a horizontal line, but this is au illusion caused 



* Rc-.d to the r!nIomat!.ic So. icty on the 13th August 1842. 



