MOVEMENTS AND DEFORMATIONS OF THE EARTH'S BODY. 543 



remarkable, that the upward movement was overshadowed. It is well 

 to note, however, that these mountain ranges are crumpled outward and 

 not inward, as might be expected if they resulted simply from the shrink- 

 age of the under side of a thin shell. The folds are sometimes nearly 

 upright and symmetrical, and sometimes inclined and asymmetrical, as 

 illustrated in the chapter referred to. Where the folds lean, the infer- 

 ence has been drawn that the active thrust came from the side of the 

 gentler slope, the folds being pushed over toward the resisting side, 

 and this seems to be commonly true. The original attitude of the 

 beds, however, has much to do with the character of the folds. ^ By a 

 slight change in the mode of thrust, sheets of paper may be so pushed 

 as to lean forward or backward at pleasure. The leaning of the folds 

 seems, therefore, a doubtful criterion for determining the direction of 

 the active movement. Mountains of the thrust type usually consist 

 of a series of folds nearly parallel to each other, the whole forming an 

 anticlinorium. 



Distribution of folded ranges. — The prevailing location of this class 

 of mountains is so generally near the borders of the continents that the 

 relation is probably significant. Dana^ long ago called attention to the 

 fact that the greatest mountain ranges stand opposite the greatest 

 ocean-basins, and he connected the elevation of the one with the depres- 

 sion of the other. One of the most notable exceptions to this relation 

 is the complex system of southern Europe, from the Pyrenees to the 

 Caucasus, and another is the Altai and connected ranges (Fig. 449). 

 The Urals and not a few minor ranges are also exceptions. It is prob- 

 ably better to regard the crumpled tracts as lying on the borders of 

 great segments of the earth that acted essentially as units, and to regard 

 the relationship to the sea as a coincidence that is only in part causal.^ 



Plateau-forming movements. — Another leading phase of crust al move- 

 ment is the settling or rising of great blocks of the crust, as though by 

 vertical rather than horizontal force. The western plateau of North 

 America and the great plateau of Thibet are gigantic examples. The 

 American plateau embraces numerous blocks which, while they have 

 been elevated together, are individually tilted in their own fashion. At 



^ Eugene A. Smith. Underthrust Folds and Faults, Am. Jour. Sci., Vol. XLV, 1893, 

 pp. 305-6. 



2 Manual of Geology, 3d ed., p. 23. 



3 For discussions of folds, see Van Hise, Sixteenth Ann. Rept. U. S. Geol. Surv., 

 Pt. I, pp. 603-632; and Willis, Thirteenth Ann. Rept., Pt. II, pp. 217-296. 



