PHYSICAL CHANGES OF THE OUTER SHELL 



85 



FIG. 72. 



FIG. 73. 



6. Why are reversed faults usually associated with folds ? Why 

 are the strikes of the two features usually 



parallel ? 



7. Why should normal faults be expected 

 to disappear downward ? 



8. Why should earthquakes be more de- 

 structive to buildings situated on unconsoli- 

 dated clay than to those on solid rock ? 



9. If of two springs in the same region, 

 one is hot and the other cold, which may be 

 supposed to have the deeper source? 



10. What phase of metamorphism is il- 

 lustrated by the change of (1) gravel to conglomerate, (2) chalk to 

 limestone, (3) peat to hard coal, (4) basalt to clay, (5) mud to slate? 



FIG. 74. 



FIG. 75. 



REFERENCES 



CHAMBERLIN and SALISBURY : Geology, Vol. I. (New York, 1904.) 

 OEIKIE, A. : Text-book of Geology, Vol. I. (London, 1903.) 

 GEIKIE, J. : Structural and Field Geology. (New York, 1905.) 

 JUKES-BROWNE : Handbook of Physical Geology. (London, 1892.) 

 VAN HISE : Principles of North American Pre-Cambrian Geology, in 



16th Ann. Kept., U.S. Geol. Surv., Pt. I, pp. 571-843. 

 A Treatise on Metamorphism; Mono. XLVII, U.S. Geol. Surv. 

 WILLIS : Mechanics of Appalachian Structure, in 13th Ann. Kept., 



U.S. Geol. Surv., Pt. II, pp. 211-282. 



