MOUNTAINS THAT NO LONGER EXIST 



423 



and folded, and all the characteristics of mountain form 

 will be present except the elevation. 



The slant of the rock layers may be such as to indicate 

 a great elevation in former times, but now only the roots 

 of the mountains are left and the region is of very moder- 

 ate elevation. Regions of this kind are found in many 

 parts of the earth. 



In the Appalachian highlands of Pennsylvania the 

 rocks show that they were once folded into ridges and 

 troughs something like those of the Jura. But now the 

 arches have been worn 

 away, and the existing 

 ridges are due to the 

 resistance which the 

 harder layers offer to 

 erosion. These ridges 

 are as likely to occur 

 where formerly the 

 troughs of the folds 

 were as in what were 

 the crests. 



The configuration of the country is not at all as it was 

 when the rocks were folded. The elevation then was 

 much greater than the highest ridges at present. If the 

 beds should be reconstructed as they now lie, they would 

 indicate a height much greater than the mountains ever 

 had at any time. Research shows that these mountains 

 have been lifted up and worn down more than once. 



Another region in which the mountains have been re- 

 duced to inconspicuous heights is the Laurentian Plateau, 

 the area around Hudson Bay. These mountains were 

 very ancient and were worn down long, long ago. In 

 some regions like southern New England, as the mountain 

 structure has been worn down, it has left here and there 



BEN NEVIS. 

 A mountain much worn down but still high. 



