366 GEOLOGY 



a small fraction of the earth's radius. Roughly speaking, each mile 

 of thickness may be conceived to support a layer of about 10 feet 

 of its own material. It is clear therefore, that a dome of shallow 

 depth could not accumulate the stresses involved in the folding 

 of great mountain systems, and that something more than a mere 

 crust of the earth has been involved in the great deformations. But 

 if the great dynamic forces which have deformed the body of the 

 earth have acted through some large part of its depth, and if the 

 rigidity of the interior is as high as the astronomical behavior of 

 the earth implies, its resistance to deformation would be adequate 

 to accumulate such stresses as are required. 



The weakness of the crust alone is such that the conclusion 

 seems imperative that, while the pliant subject of minor and 

 frequent warpings, it is wholly incompetent to be the medium of 

 the great deformations. Such deformations apparently involve 

 a large part of the body of the earth, and imply a high state of 

 effective rigidity. 



A few references on crustal movements. Lyell, Principles of Geology, 

 Vol. II, p. 235; Reade, Origin of Mountain Ranges, and Evolution of Earth 

 Structure; Fisher, Physics of the Earth's Crust; Button, Greater Problems 

 of Physical Geology, Bull. Phil. Soc. of Washington, Vol. XI, p. 52; also Am. 

 Jour, of ScL, Vol. VIII (1874), p. 121, and Geology of the High Plateaus of 

 Utah (1880); Dana, Manual of Geol., 4th ed., p. 345 et seq.; Woodward, 

 Mathematical Theories of the Earth, Smithsonian Rept. for 1890, p. 196; 

 Willis, The Mechanics of the Appalachian Structures, 13th Ann. Report, 

 U. S. Geol. Surv., Pt. II (1893), pp. 211-282; LeConte, Theories of Mountain 

 Origin, Jour. Geol., Vol. I (1893), p. 542; Gilbert, Jour. Geol., Vol. Ill (1895), 

 p. 333, and Bull. Phil. Soc. of Washington, Vol. XIII (1895), p. 31; Van 

 Hise, Earth Movements, Trans. Wis. Acad. Sci., Arts and Let., Vol. II (1898), 

 pp. 512-514; Estimates and Causes of Crustal Shortening, Jour. Geol., Vol. 

 VI (1898), U. S. Geol. Surv. (1904), pp. 924-931; A. Geikie, Text-book of 

 Geology, 4th ed., pp. 672-702; Chamberlin and Salisbury, Geology, Vol. I, 

 Chapter IX. 



Map work. Various phases of diastrophism are shown on the maps of the 

 U. S. Geological Survey listed on pages 432-433 of Salisbury's Physiography, 

 Advanced Course. Plates CLXV to CLXVII of Professional Paper 60 show 

 certain topographic features due to faults. The folios, especially of mountain 

 regions, afford other illustrations, best seen in the Structure Section Sheets. 



