18 THREE GEOLOGICAL PROVINCES. 



diagram illustrating the general types of displacement heretofore discussed. 

 A represents a Simple Anticlinal displacement ; 13 a Uinta displacement ; 

 C a Kaibab displacement ; D a Basin Range displacement ; and E a Zone 

 of Diverse displacement, 



MOUNTAINS COMPOSED IN WHOLE OR IN PART OF EXTRA- 



VASATED MATERIAL. 



We are not able in the present state of our knowledge to draw legiti- 

 mate conclusions concerning the relation of the eruptive rocks so widely 

 distributed through all three of these geological provinces, but the following 

 types of structure have been observed. 



VII. TABLE MOUNTAIN STRUCTURE. 



We often find beds of sedimentary strata preserved from erosion by a 

 capping of lava. Such are usually called table mountains; the underlying 

 strata may be horizontal or inclined. Earlier stages of this structure are 

 seen in mesas or low tables, and sometimes in valleys or gulches which 

 have been filled with extravasated material, and erosion has proceeded to a 

 limited extent on either side of these harder masses carrying away the 

 softer sedimentary material and leaving the harder volcanic rocks in the 

 midst of the valley, and this may have an elevation lesser or greater than 

 that of the adjacent country beyond the rim of the valley. 



A fine example of a table mountain is found in Pilot Butte, in Wyo- 

 ming Territory. 



VIII. UINKARET STRUCTURE. 



Simple sheets of lava may be poured into a valley or on a plain, and 

 serve as a protection to the sedimentary beds which are immediately under- 

 lying them and, as the erosion of the adjacent country not thus protected 

 progresses, new vents may be formed along the edges of such sheets and 

 at a lower level. Still erosion progresses, and still new floods of lava are 

 poured out, and still at lower levels, until a mountain is left behind with its 

 central mass composed of sedimentary material, but covered on the summit 



