240 Mr J . D. Dana on the Origin of Continents. 



But there are ridges which add five or six thousand feet to 

 the chain : these form a crest to parts of the range, but are 

 not properly the range itself, though often so recognised. 

 The Rocky Mountains appear, then, to he another effect of 

 contraction, viz. a gradual swelling of the surface, accom- 

 panied by fissures and dislocations over its area. These dis- 

 locations are very marked in the sandstone, just east of the 

 summit. Thus each great oceanic depression, the Atlantic 

 and Pacific, has its border range of heights thrown up by the 

 very contraction which occasioned the depression ; and be- 

 tween lies a vast plain, scarcely affected at all by these 

 changes, the great central area of the continent. This view 

 is farther sustained by finding that the efi^ects of fire are 

 most apparent on the ocean side of the mountains, precisely 

 as about the Appalachians, yet to a more remarkable extent.* 

 Indeed, there are no remains of volcanoes, or their ejections, 

 to the east of the summit ; while to the west, the country of 

 Oregon is in many parts buried beneath basaltic or other 

 volcanic rocks, and several existing volcanic cones have been 

 described. Still farther, we observe a second, a third, and 

 even a fourth, parallel range of heights from the summit of 

 the mountains to the coast ; and the third (the Cascade 

 range) rivals the Rocky Mountains in the height of some of 

 its snowy peaks. Vast fissures were opened to the fires be- 

 low, as these ranges indicate, and some of the vents have not 



* The same is the general character of the Andes. In an account of the 

 geology of Chile, M. I. Domeyko says, speaking of the Andes in the latitude of 

 Copiapo, " En regardant du cote de I'Ouest, on voit un bouleversement complet 

 dans le terrain souleve : des failles et dechirements, des escarpments a pic, des 

 stratifications contourne^s et interrompues. En portant onsuite la vue du cote 

 de I'est, on voit des pentes douces, des bancs de rochers presque horizontaux et 

 rarement interrompus. 



" Tout announce que le principal raouvement qui survint a I'epoquc de la 

 formation des Andes arriva du cote de V Quest, c'est-a-dire du cote ou une ligne 

 d'escarpments qui marquent le rivage actuel de I'Ocean depuis le Cap Horn 

 jusqu' aux Montagues Ilocheuses, continue a se soulever d'une maniere lente et 

 a peine perceptible, au mugissement de bruits souterrains et sous I'influence des 

 tremblements de lerre repet^s," — Annates des Mines, iv. ser., ix., 413, 2nd. liv. 

 1846, 



