AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[THIRD SERIES] 
Art. XL—A Theory of the Formation of the great Features of 
the Karth’s Surface; by JoserpH LEConvs, Prof. Geol. and 
at. Hist, University of California. 
that this paper might, very appropriately, have been entitled 
A general theory of igneous agencies.” The general and 
first effect of igneous agency is, evidently, the formation of 
Continents, sea bottoms and mountain chains. Volcanoes and 
earthquakes are secondary phenomena—they are but occa- 
Stonal accidents attending the slow march of these grander effects. 
ceording to Humboldt, all the effects grouped under the 
Seneral head of igneous agency are the result of “the reaction 
Y the interior on the crust of the earth.” This formula, although 
T too vague and general to deserve the name of a theory, 
Must, we believe, form the point of departure of every true 
theory. But in de arting from this vague formula, only the 
most confused sins contradictory notions seem to prevail 
Amongst geologists. We have therefore thought that, on a sub- 
Ject of such vital importance, lying as it does at the very found- 
ation of theoretic geology, any light, or even m8 more defi- 
hite statement than now exists, might be considered timely. 
I have, for many years, thought much on the subject, and 
_ Stfiven to emerge from the chaos which now exists into some- 
thing like clearness of conception. I here present, with some 
hesitation, the results, hoping that they may serve, at least, as 
ints in the right direction. ‘ 
Aw. Jour, 8c1.—Tarap — Vou. 1V, No, 28.—Nov., 1872. 
