FORMATION OF MOUNTAINS. 823 



Massachusetts and Vermont, a western section of the Green Moun- 

 tains. 



3. Consequent Character of Mountain Chains. — (1.) Mountain 

 chains are combinations of mountain ranges of the synclinorial kind, 

 with usually other results as to altitude and fracture from subsequent 

 geanticlinal movements. It has been already explained that the Ap- 

 palachian Chain and the Rocky Mountains are of polygenetic origin 

 (p. 796) ; and these are examples of the general fact. The geanti- 

 clinal movements may have followed soon upon the making of the 

 range, or have accompanied it ; but, in general, they have come long 

 afterward. The Wahsatch Mountains now have a height of 12,000 

 to 14,000 feet above the sea level; but if the mass of the Rocky 

 Mountains had not been raised during the Tertiary, after they were 

 made, 10,000 feet, their altitude would have little exceeded that of the 

 Appalachians. And while a geanticlinal movement of 10,000 feet in 

 elevation has taken place on the western portion of the continent 

 since the Cretaceous period, one of 500 feet, to, perhaps, 1,000 feet, 

 has occurred on the Atlantic border, adding this much to the elevations 

 of the Appalachians and other mountain areas. 



(2.) Successive synclinoria have rarely been made with a common 

 axis. The region of a synclinorium ends in becoming a part of the 

 stiff, unyielding and stable crust, apparently because of the solidifi- 

 cation, and often, in parts, the complete crystallization, undergone dur- 

 ing its formation. The locus of the next progressing geosynclinal 

 is hence likely to be on one side or the other of the axis of the pre- 

 ceding finished synclinoria. The range of the Adirondacks lies to 

 the west of the Green Mountain range, and that of the Blue Ridge of 

 Virginia and North Carolina, also Archaean, to the east of the Appa- 

 lachian range ; and after the last mentioned synclinorial range was 

 completed, another was in progress to the eastward of the former syn- 

 clinoria, both in New England and to the southwest — that of the 

 Triassico- Jurassic beds. This shifting of the region to one side and 

 the other has tended to give the great width to the mountain chains. 



(3.) Further, the thickening of the earth's crust with the progress 

 of time has caused a gradual change in the character of mountain- 

 making. 



After the crust had become thickened by the earth's internal cool- 

 ing through the ages, and had been stiffened also by the plication and 

 solidification, and partly the crystallization, of the strata of the super- 

 crust, geosynclinals became less a possibility ; and, consequently, the 

 chief movement in mountain regions, caused by the ever-continuing 

 lateral pressure, was an upward one, and mountain chains thereby re- 

 ceived their great heights largely in the Tertiary. For the same 



