THE ORIGIN OF MOUNTAINS. 
6l 
Alps at a minimum of 1 20,000 metres* The original 
breadth of the strata forming the Aarmassif was at 
least double the present, and the same may be said 
of the central range. The Appalachians are calcu- 
lated to be compressed from 150 miles to 65. 
It very seldom happens that such a range of 
mountains consists of a single fold. There are 
generally several, one being as a rule formed first, 
and others outwards in succession. In both the 
Alps and the Jura, the southern folds are the oldest. 
In Central America, again, there are several longi- 
tudinal ranges, and the volcanoes are generally 
situated on cross lines of fracture, so that they are 
in rows, at right angles to the general direction of 
the mountains, and in almost every case the outer 
crater, or that towards the Pacific, is the only one 
now active. 
A glance at any good map of the Jura will show 
a succession of ridges running parallel to one another 
in a slightly curved line from south-west to north- 
east. That these ridges are due to folds of the 
Earth’s surface is clear from the following figure 
(Fig. 5) in Jaccard’s work on the Geology of the 
Jura, showing a section from B renets due South to 
Neuchatel by Le Locle. These folds are com- 
* Mcchanismus d. Gebirgsbildung , v. 2. 
