J. LeConte—Structure and Origin of Mountains. 107 
distinguished vulcanologist Scrope, and at least deserves the 
serious attention of geologists. If this be the true origin of 
voleanic water, then in its escape we would have another 
important factor of contraction, although perhaps, by itself, 
also inadequate.+ 
a word, it is probable that in the present condition of 
science we do not know all the causes of contraction. But the 
jact of contraction is one thing and the cause of contraction 
another and quite a different thing. The fact of contraction is 
not conditioned on our knowledge of the causes of contraction 
but rests wholly upon the phenomena of structure. Tf loss of heat 
be inadequate, then we must seek some additional cause. If 
all known causes be inadequate, then we must frankly acknow- 
ledge our ignorance and seek still other causes yet unknown. 
The great importance of separating these two things and 
keeping them distinct in the mind, may be illustrated by ex- 
amples. In nearly all complex subjects there are two stages of 
theorizing and therefore two successive theories. e one dis- 
cusses and determines the laws of phenomena and the condi- 
oneny of the latter, the physical, and in fact forms its basis ; 
ut not vice versa. So again it is certain that glaciers conform 
educes to law, and consistently explains all the phenomena of 
glacial motion. But still the question remains. By virtue of 
* Cambridge Phil. Trans., vol. xii. part II; Feb., 1875. 
+ Even while writing this, I see that Tschermak brings forward a similar theory 
of vuleanism and connects it with many cosmic phenomena, such as r explo 
Sions of gas, new stars, explosion of meteors, &e.—({Geol Mag., vol. iv, 569, 1877. 
