1844.] LAVA STREAMS HOW THEY TERMINATE. 49 



certaine vitesse, caracteres que j'ai observes sur toutes sortes 

 de pentes depuis 33 jusqu'a 2 et que je n'ai cesse d'observer 

 que la ou les coulees se sont ^arretees faute de pente, consiste en 

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

 digue de scories accumulees qui rappelle par sa forme la moraine 

 d' un glacier ; digue que s' eleve constamment a une hauteur 

 superieure a celle a laquelle la coulee est reduite a la fin du 

 mouvement, et qui marque le maximum de hauteur qu'elle a 

 atteint dans le moment de son plus grand gonflement. Souvent 

 aussi les coulees presentent de pareilles digues vers leur milieu, 

 lorsqu'elles sont partagees en plusieurs en courants distincts 

 coulant Tun a cote de Fautre."* 



VII. The termination of a lava stream on a level or slightly 

 inclined surface due to its increasing viscidity, presents appear- 

 ances almost identical with those of a glacier. The same pro- 

 tuberant convexity of surface, the same steeply-inclined sides 

 and front, and nearly the same ground-plan, all bespeak a simi- 

 larity in the circumstances of motion. I may add, that in some 

 experiments which I made some years ago upon the flowing of 

 melted iron in narrow channels, and upon small slopes, with a 

 view to illustrate some phenomena of lava streams, before I had 

 commenced a particular study of glaciers, I arrived at similar 

 results, and obtained the same convexity of surface which is 

 produced in the plaster models before cited. 



It is very interesting to observe how many intelligent per- 

 sons have been struck with the similarity between glaciers and 

 lava streams, without, however, pushing the parallel beyond a 

 general resemblance. M. Elie de Beaumont, we have seen, 

 speaks of the moraines of volcanoes ; but in various parts of his 

 writings, as well as those of his colleague, M. Dufrenoy, we find 

 the mention of glaciers as continually suggested to his mind 

 when surveying the wastes of Etna and Vesuvius. One of these 

 passages is the following : " L'ecorce superieure d'une coulee 

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



* E. de Beaumont, Recherches sur le Mont Etna, p. 184. 

 E 



