590 HISTORY OF GEOLOGY. 



physical history of the earth, and therefore to geo- 

 logy, we may notice all the general laws which refer 

 to its temperature; both the laws of climate, as 

 determined by the isothermal lines, which Hum- 

 boldt has drawn, bf the aid of very numerous 

 observations made in all parts of the world; and 

 also those still more curious facts, of the increase of 

 temperature which takes place as we descend in the 

 solid mass. The latter circumstance, after being 

 for a while rejected as a fable, or explained away 

 as an accident, is now generally acknowledged to 

 be the true state of things in many distant parts 

 of the globe, and probably in all. 



Again, to turn to cases of another kind : some 

 writers have endeavoured to state in a general man- 

 ner laws according to which the members of the 

 geological series succeed each other ; and to reduce 

 apparent anomalies to order of a wider kind. Among 

 those who have written with such views, we may 

 notice Alexander von Humboldt, always, and in 

 all sciences, foremost in the race of generalization. 

 In his attempt to extend the doctrine of geological 

 equivalents from the rocks of Europe- to those of 

 the Andes, he has marked by appropriate terms the 

 general modes of geological succession. "I have 

 insisted," he says 3 , "principally upon the phenomena 

 of alternation, oscillation, and local suppression, 

 and on those presented by the passages' of forma- 



a Gissement des Roches dans les deux Hemispheres, 1823. 

 3 Pref. p. vi. 



