368 PHYSICAL GEOLOGY 



antedating the last elevation. The Sierra Nevadas, after folding, 

 were peneplained and were later elevated along a great fault on the 

 east, and their height is being increased at the present time. It is 

 thus seen that the elevation of high mountains may be due to verti- 

 cal movements, without the aid of folding. 



The Distribution of Mountains. — Attention has long been called 

 to the fact that the mountain ranges of the Pacific — the Andes, 

 western ranges of North America, etc. — are situated near the edges 

 of the continents, and the generalization has been made that moun- 

 tains are usually located near the oceans, the higher mountains 

 bordering the deepest basins. It is also to be noted that many 

 exceptions exist : the Alps, Caucasus, Urals, and Himalayas are 

 situated at considerable distances inland. The distribution of moun- 

 tains has led to two theories as to the position of the geosynclines 

 in which the sediments forming them were accumulated ; one hold- 

 ing that the geosynclines existed at the edges of the continents, the 

 other that they were between land masses. The apparent exceptions 

 to the latter theory are attributed to the subsequent sinking of lands 

 which formerly existed near the present shores of the oceans bordered 

 by mountains. According to this theory, for example, the Alpine 

 geosyncline existed between the African continent and the ancient 

 land masses on rhe north; the Appalachian geosyncline, between 

 the Piedmont land on the east and other ancient lands on the north 

 and west (p. 477) ; the Himalayas, between the Indian peninsula 

 and land to the north. 



Permanence of Continents and Ocean Basins. — It is quite 

 generally agreed by geologists that the ocean basins and the con- 

 tinental platforms have been very much as now for many millions 

 of years. By this is meant that the present continents have not been 

 covered by oceans thousands of feet deep, nor have the ocean depths 

 been dry land over wide areas. The proof of the former lies in the 

 fact that no deep-sea sediments have ever been found in the sedi- 

 mentary rocks of the continents, the continents having been covered 

 repeatedly by shallow seas (called epicontinental, p. 405), but never 

 by any of great depth. Of the latter no positive proof has been 

 advanced, but on the contrary the distribution of animals and plants 

 in the past gives reason for believing that land connections once 

 existed between South America and Africa, North America and Eu- 

 rope, and Australia and Africa. 



Age of Mountains. — This subject will be more fully discussed 



