REVIEWS 511 



Although traces of heHum occur in most natural gas, noteworthy 

 proportions have been found only in gas rich in nitrogen. The per- 

 centage in helium, moreover, seems to depend, in a measure, on the 

 percentage of nitrogen, though there is not direct proportionality 

 between the two. Some of the Kansas gases contain about 85 per cent 

 of nitrogen and 2 per cent of helium. 



After a discussion of the occurrence of helium in minerals and rocks, 

 in mine gases and in the gases of mineral springs, volcanoes and fumeroles, 

 the theories that have been advanced in explanation of the origin of the 

 helium in natural gases are discussed. While recognizing that the origin 

 of the hehum is still a matter of great uncertainty, the writer is inclined 

 to favor the view that the helium is derived from deposits of uraniiun 

 and thorium, probably disseminated through the strata not far beneath 

 the horizons at which the helium gas occurs. 



E. S. Basiin 



The Economic Aspects of Geology. By C. K. Leith. New York: 

 Henry Holt and Company, 192 1. 



Because each year modern industry is becoming more technical, 

 industrial progress has come to stride pace after pace with the develop- 

 ment of science. Geology has shared with other sciences in the tighten- 

 ing of the bonds between science and industry. It is no longer necessary, 

 as it was a generation ago, for the geologist to be continually bringing 

 before the public the practical potentialities of his science; certain 

 industries are now even snatching the half-fledged geologists from their 

 academic nests. The increasing industrial importance of geology lays a 

 new responsibility upon those engaged in the training of economic 

 geologists, and Professor Leith's book, an embodiment of lectures given 

 at the University of Wisconsin, drives home to the geology student in 

 vigorous fashion not only the fundamental facts of useful mineral 

 occurrence but also the role which each of these minerals plays in the 

 economic Hfe of the nation and of the world. The book is, in fact, an 

 outgrowth of its author's war-time experiences during which he dis- 

 tinguished himself as a leader in the first real inventory of her mineral 

 resources that the United States had ever taken. 



The work is adapted to the use of students having an elementary 

 knowledge of geology, such, for example, as is commonly acquired in the 

 first year's work in college geology. While adapted for the use of 



