84 VISCOUS THEORY OF GLACIER MOTION. [1845. 



as characteristic of lava streams as well as glaciers, in the pre- 

 ceding extract, is perfectly borne out by the view of the lava of 

 1831 given by Mr. Auldjo, and already cited ; the same appear- 

 ance is mentioned by M. Elie de Beaumont in his account of 

 Etna in the following terms : " Une des circonstances que les 

 coulees de lava presentent le plus invariablement .... con- 

 siste en ce que chaque coulee est flanquee de part et d'autre par 

 une digue de scories accumulees qui rapellent par sa forme la 

 moraine d'un glacier, . . . souvent aussi les coulees presentent 

 de pareilles digues vers leur milieu, lorsqu'elles sont partagees 

 en plusieurs courants distincts coulant 1'un a cote de 1'autre."* 



In another place the same author compares the movement 

 of the upper crust of the lava to that of glaciers according to 

 the then prevalent theory : " L'ecorce superieure d'une coulee 

 separee de 1'ecorce inferieure et du sol sousjacent par une cer- 

 taine epaisseur de lave liquide, on du moins visqueuse, se trouve 

 dans un etat comparable a celui d'un glacier, qui, ne pouvant 

 adherer au sol sousjacent a cause de la fusion continuelle de sa 

 couche inferieure, se trouve contraint de glisser."f 



Finally, M. Rendu, Bishop of Annecy, in his excellent 

 Essay on Glaciers, refers in one passage (and I believe in one 

 only) to the possible analogy with a lava stream, " [le glacier] 

 s'affaisse-t-il sur lui-meme pour couler le long des pentes comme 

 le ferait une lave a la fois ductile et liquide ?"J 



The following considerations seem to show more than a 

 general external analogy between lava streams and glaciers. 



Their velocities are sometimes equally slow. Although 

 common lava is nearly as liquid as melted iron, when it issues 



* R'echerches sur le Mont Etna, p. 184. Published in the Memoires pour 

 servir a une Description Geologique de la France, tome iv. 1838. 



f Recherches sur le Mont Etna, p. 177. 



J Theorie des Glaciers, Mem. de 1' Academic de Savoie, tome x. p. 93, published 

 1841. [I may perhaps be allowed to add my own impressions to the same effect in 

 1841, founded, for the most part (at that time), on the same general and external 

 analogies which had guided my predecessors : " None who has ever seen, or even 

 clearly conceived a lava-stream, can fail to find in it the nearest analogue of a 

 glacier. Stiff and rigid as it appears, it either flows or has once flowed." Ed. Rev., 

 April 1842, p. 53.] 



