EARTHQUAKES 425 



The peaks have been formed by erosion, and their pecul- 

 iarities are due to the different kinds and positions of the 

 rocks from which they have been carved. 



The younger mountains which have not been subjected 

 to erosion for a long time do not show the peak and ridge 

 structure. Their personal characteristics have not had 

 time enough yet to assert themselves. All these peaks 

 are the result, not only of original uplift, but of subsequent 

 carving. 



THE TETON RANGE. 



201. Mountain Ranges. As a rule mountains are found 

 in ranges. The mountains in the range are by no means 

 all the same elevation, nor is the range necessarily contin- 

 uous, there being often gaps along its course. Neither 

 were all ranges in a mountain region elevated at the same 

 time. Those which make up the mountain region of the 

 western United States differ much in the time of their 

 elevation. 



202. Earthquakes. In mountain regions which are 

 young or still growing, earthquakes are not uncommon. 

 These are due to breaks or slips of a few inches or a few 

 feet in the rock structure. From the place at which the 

 break or slip takes place the motion is transmitted through 



