BO'S W. T. LEE BUILDIXG OF SOUTHERX ROCKY MOUXTAIXS 



l3e cut off' from its siirroiinclings, deriving no support from them. Uni- 

 form pressure over the surface then gives the same yielding at all points 

 of the section and for sections of all sizes. For any small section con- 

 Jiected with the surrounding crusty the yielding computed by formulas 

 (1), (2) J or (3) is much too great. 



If, however, we consider a section havino- a verv lar^'e area and con- 

 nected, as in nature, with its surroundings, these formulas, particularly 

 -case (2) formula (2), give an indication of the approximate yielding to 

 be expected in the center of the area; for the outer portions of the area 

 .are so pressed down by the load on them that they afford little supjDort 

 to the central portion, and the latter yields almost as much as if it were 

 severed from its surroundings. The extent of the area that may be con- 

 sidered '^•'large'' must evidently increase with the rigidity of the crust. 

 For extremelv laro-e areas, the curvature of the earth's surface must also 

 he considered, and its effect is to diminish the vieldino- somewhat. 



