Ch. 7] REFERENCES 145 



is essential if construction in the arctic and northern latitudes is to 

 succeed. A beginning has been made, but "permafrost" studies in 

 relationship to construction have in a sense only begun. 



Additional studies of precompressed soils, such as those unloaded 

 by erosion, exposed at the base of deep cuts, found in the beds of 

 drained lakes and swamps, and under long-departed ice loadings, 

 would be helpful. 



Investigations of the subgrade beneath existing major highway 

 and airstrip pavements in relationship to similar natural soils adja- 

 cent to these features might be worth while. 



Refinements of geophysical exploration of soils and closer correla- 

 tion between geophysical and soil mechanics investigations is neces- 

 sary. Already seismic and electrical resistivity studies have proved 

 themselves in highway construction and foundation work. In some 

 quarters caution is indicated, because at present overly enthusiastic 

 acceptance of electrical resistivity methods may obscure the fact that 

 check borings are essential and it is not a single "tool" but must be 

 used in conjunction with others. 



Because of the varied topographic and climatic environments as 

 well as the countless variations in consolidated and unconsolidated 

 sediments of diverse origins and histories, the research possibilities 

 are infinite. So long as men travel on or take off and land aircraft 

 on the surface of the earth, new and continuing research will be re- 

 quired. 



REFERENCES 



Cady, G. H. (1921). Coal resources of District 11: Illinois Mining Investigations, 



III. Geol. Survey, Coop. Mining Ser., Bull. 26. 

 Campen, W. H., and Smith, J. R. (1942). Discussion on soil test for the design 



of runway pavements: Proc. Highway Research Board, p. 174. 

 E. I. du Pont de Nemours & Co., Inc. (1939). Blaster's Handbook: pp. 132-137. 

 * Federal Works Agency, Public Roads Administration (1943). Principles of 



highway construction as applied to airports, flight strips, and other landing 



areas for aircraft. 

 Grim, R. E. (1942). Modern concepts of the clay minerals: Jour. Geol., vol. 50, 



pp. 225-275. 

 Hardy, R. M. (1946). Permanently frozen ground and foundation design: Eng. 



Inst, of Canada, vol. 29, pp. 4-10. 

 Herbert, C. A., and Rutledge, J. J. (1927). Subsidence due to coal mining in 



Illinois: U. S. Dept. of Commerce, Bur. Mines, Bull. 238. 

 Hewes, Laurence I. (1942). American Highway Practice: John Wiley & Sons, 



New York, vol. I. 

 Hittle, J. E., and Goetz, W. H. (1946). Factors influencing the load-carrying 



* Articles of comprehensive scope or containing extensive bibliographies. 



