204 FIRST YEAR COURSE IN GENERAL SCIENCE 



quartz or limestone. After a great thickness of sediment 

 had been deposited, its weight weakened the rock beneath. 

 Then contraction and the pressure of the ocean block against 

 the continental block wrinkled the crust and thus a fold was 

 made along the weakened rock. The result was a slowly 



FIG. 105. FOLDED ROCK EXPOSED IN A RAILROAD CUT, 

 BERTON, VIRGINIA 



This is not a part of a mountain now, but it illustrates the first form 

 of some mountains. 1. Is this igneous or sedimentary rock? How 

 do you judge? 2. The camera case upon the rock is about 10 in. long. 

 Estimate the height of the fold. 



uprising fold, or sometimes two or even many parallel folds, 

 as in the 'Appalachian Mountain system. In this way most 

 of the great mountain systems of the world were formed. 

 When they were uplifted, they were near the borders of ah 

 ocean or a great interior sea! They have since been worn 

 down so much that all appearance of folding is gone. 



