ORIGIISr OF FOLDED MOUNTAINS PROUTY 301 



crystalline rock are either melted or turned to glassy material. Be- 

 cause of the advance of the continental border over the area of 

 foundered rock, the increase in volume of the foundered rock through 

 melting or vitrification would cause a gradual elevation of both the 

 geosynclinal and the adjacent continental areas. 



This theory, then, accounts for the formation of the arcuate moun- 

 tain pattern, the folding, the tensional faulting farther inland, and 

 the later uplift of the folded mountains and the bordering conti- 

 nental areas such, for instance, as the Colorado Plateau. This 

 theory, along with that of Joly's, favors the possibility of a certain 

 amount of continental drift. 



The weakness of the theory lies in its assuming such great mobility 

 for the glassy basalt and in the nonconformity of the theory with 

 the structure of the tensional basins. 



JOLY'S RADIOACTIVE THEORY 



According to the Joly radioactive theory all known rocks have 

 radioactive substances chiefly in the form of uranium or thorium. 

 These two heavy atomic weight elements are slowly changing to sub- 

 stances of less atomic weight and finally to lead. In the change heat 

 is given off. Man has been unable in any way to change the rate 

 of decomposition by extreme temperature and pressure changes. At 

 the known rate of decomposition one-half of the uranium will have 

 disappeared in 5,000 million years and one-half the thorium in 

 18,000 million years. Granites and acid igneous rocks contain about 

 twice as much radium as the basic igneous rocks and the sedimentary 

 rocks. The loss of heat at the earth's surface is known to be about 

 the same as the computed amount generated by radioactive substances 

 in the 35-mile crust. In the thicker continental crusts more heat is 

 generated than is lost, and everywhere in the earth beneath the 

 crust, radioactive heat is constantly accumulating. The latent heat 

 of fusion of basalt is 100 calories per gram. It w^ould, therefore, 

 take about 30,000,000 years for sufficient heat to accumulate to 

 bring the subcrustal basalt to the melting point. 



Radioactive substances have been undergoing decomposition and 

 causing rise in temperature since the earliest geologic times as shown 

 by radioactive haloes in Archean rocks, nearly two billion years old. 



When fusion of the basaltic crust takes place, convection currents 

 concentrate the heat on the crystalline rocks of the overlying crust. 

 This crust is gradually thinned by melting from below, until the more 

 rapid loss of heat, through the thinned shell, checks the process. If 

 we assume with Professor Joly a 70-mile thickness of melting, the 

 general 10 percent volume increase will lengthen the earth's radius 

 by 6.5 miles. This elevation would cause general tension and crack- 



