J. LeConte—Structure and Origin of Mountains. 95 
Arr. X.—On the Structure and Origin of Mountains, with special 
reference to recent objections to the “Contractional Theory ;” by 
JOSEPH LECoNTE. 
(Read before the National Academy of Sciences, April 19, 1878.) 
In order to write intelligibly on this subject it is necessary 
first of all to define clearly in what sense we shall use the word 
mountain. In ular and even in scientific language this 
word is used to express every considerable elevation above the 
general level of the earth surface, whatever be its extent or its 
mode of origin. It is applied equally to a complex svstem of 
ranges formed at different times, such as the Andes, the North 
American Cordilleras, or the Appalachian ; or to each one of 
the components of such a system, as for example the Coast 
Range, the Sierra or the Wahsatch ; or to each one of the com- 
ranges formed at different times a mountai 
Each monogenetic* component of such a system, such as the Sierra 
) 
the formation of Ranges. For, on the one hand a mountain- 
proper—in all cases they belong to the category of mountain 
decay, not to that of mountain-origin. It seems to me that 
much of the refined classifications, and of the minute divisions 
and subdivisions of types of mountains, in which some recent 
writers have indulged is the result of an imperfect recognition 
of the distinctions enforced above. Limited, as above, moun- 
tain ranges are, I believe, always formed by horizontal pressure 
* A well chosen word | reatly ct. We are in- 
Jet isha bein oe often 2 pnes Sethe apes Aare = 
te, 
