CLASSIFICATION OF MOUNTAIN RANGES. 675 



ain masses and plateaus, while the crust segments have been only 

 slightly tilted and sometimes lie wholly beneath the sea-level. 

 Such eruptions form the Cascade Range, the mountainous plateaus 

 of Iceland and the much-eroded Faroe Islands, the Deccan plateau 

 in India, the volcanic chains of the Sunda, Kurile, and Aleutian 

 Islands, and the Hawaiian Island belt. 



The Cascade Range is a typical example of this class, having 

 an extent of more than 500 miles from south to north across Ore- 

 gon and Washington, showing a thickness of nearly 4,000 feet of 

 lava where it is cut through by the Columbia, and bearing here 

 and there volcanic peaks which rise to altitudes 10,000 to 14,000 

 feet above the sea. The eruptions producing this range took 

 place during late Tertiary and early Quaternary time, being con- 

 temporaneous with the faulting and tilting of the Basin ranges, 

 the Wahsatch, and the Sierra Nevada, and with the folding and 

 upbuilding of the Coast Range. As Jamieson and Alexander Win- 

 chell have well suggested, the outpouring of the vast lava floods 

 of the Cordilleran belt in the United States, a portion of which 

 forms the Cascade Range, was probably in large part or wholly 

 dependent on movements of elevation and subsidence of the adja- 

 cent glaciated area. Another erupted range, on a smaller scale, 

 but very interesting in its details as described by Russell, belong- 

 ing to the Quaternary era, and partly to the recent epoch, lies 

 close south of Lake Mono, in California. 



6. Eroded Mountain Ranges. The form and contour of 

 nearly all mountains, excepting volcanic cones, have been given 

 to them by the sculpturing agencies of subaerial denudation. 

 This is true of each of the foregoing classes, where mountain- 

 building energy has supplied the mass, but erosion has shaped 

 the slopes, ridges, and peaks, the ravines and valleys. These five 

 classes of mountain ranges have been sculptured by erosion, where 

 previous mountain-building has raised limited areas to an excep- 

 tional altitude. But besides these orogenic upheavals, there have 

 been broader uplifts of the whole or large parts of continents, 

 which Gilbert and White have called epirogenic movements. The 

 sixth class of mountain ranges, here to be noticed, is distinguished 

 from all the preceding by its comprising mountains which owe 

 their origin to no definite mountain-building process, being sim- 

 ply remnants of extensive areas which have been uplifted by 

 epirogenic energy as great plains and since have been deeply 

 eroded. 



The plains which slowly rise from the Mississippi Valley and 

 Manitoba westward to the foot of the Rocky Mountains afford ex- 

 amples of this type of mountain structure. Perhaps the most strik- 

 ing is the range of the Crazy Mountains in Montana, which lies 

 immediately north of the Yellowstone River near Livingston, and 



