THE MOUNTAIN FKAMEWORK. 113 



bottom, and the walls of the gap were left to rise precipitously 

 on each side. Other mountains have been rent by fissures. 

 These generally run lengthwise of the range most frequently 

 along the center. When they exist, the strata on one side are 

 generally found depressed below the level of the corresponding 

 strata on the other side. Such a case is a fault. In the Appa- 

 lachians are faults of five thousand to twenty thousand feet. 

 A greater one cuts through the Uintas. The Sierra Nevada, 

 for three hundred miles, has been split lengthwise along the 

 middle, and the eastern half, for a large part of the distance, 

 has gone down three thousand to ten thousand feet. So the 

 west half the Wahsatch went down forty thousand feet for a 

 length of at least one hundred miles. 



Of mountains of relief, like the Catskills and the Cumber- 

 land Table Land, something has already been said in Talk IX, 

 and nothing more is necessary here. Mountains composed of 

 volcanic accumulations are mentioned in Talks XV and XVI. 



. How THE MOUNTAIN KRAMEWORK is 



MOUNTAIN FORMATION. 



BY what machinery were these mountain masses upraised? 

 By what motive force was it actuated? When we look up 

 toward the sky and see the form of Mont Blanc profiled 

 against the clear blue far away far up where the white 

 clouds cap the mountain's hoary head, we realize partially 

 that an enormous power has been exerted ; we reflect that the 

 upraising of a mountain was as truly a mechanical work as 

 the erection of the obelisk in Central Park. Let us try to 

 reproduce to imagination the process by which Nature builds 

 the great mountains the great mountains of upheaval. 



Generations past, which had witnessed the tremendous 

 power of Vesuvius and ^Etna, thought the volcano adequate 

 for the production both of earthquakes and mountains. It 

 was steam and gases trying to find vent, they said, which 



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