DESCRIPTION OF ILLUSTRATIONS. 175 



The surface lines, the outcrop of the beds along these lines, and the thick- 

 ness of the beds are factors sufficient for the construction of the sections and 

 diagrams, but the observed dips and strikes afford many valuable checks in 

 their construction. 



A single diagram represents displacement and degradation in two dimen- 

 sions; that is, in a vertical plane from south to north across the axis of up- 

 heaval. A group of these diagrams constructed on parallel planes, separated 

 by equal intervals, and having the scale of these intervals in the group the 

 same as the vertical and horizontal scale of each diagram, serves to repre- 

 sent displacement and degradation in three dimensions. 



Stereogram. To more fully bring the displacement into visual compre- 

 hension, the stereogram, Plate III, has been constructed. Here the lines 

 representing the level of the sea, and those representing the present surface 

 are omitted, leaving only the displacement lines; and between these others 

 have been interpolated, so that the intervals are but 3, 500 feet; and this has 

 the effect of projecting the region in relief, as it would appear in a bird's-eye 

 view had there been displacement but no degradation. To fully compre- 

 hend the meaning of this stereogram, it is necessary to remember that every 

 deviation of a line from horizontality represents a corresponding inclination 

 of the beds, and careful inspection will show that absolute horizontality very 

 rarely occurs. The stereogram fails to represent the abruptness of flexure 

 in some places, as the lines of displacement show the intersection of vertical 

 parallel planes with the summit of the reproduced bed, and these planes have 

 a north and south direction. Wherever they do not cross a flexure in the 

 direction of the dip, but to a greater or less extent oblique to it, to such 

 extent do the displacement lines fail to represent the abruptness of the flexure 

 or angle of dip ; in other words, the stereogram does not fully represent dis- 

 placement in an east and west direction. But the axis of flexure in the Uinta 

 Mountains has an easterly and westerly direction, and all other displace- 

 ments are subsidiary to this; and as the displacement lines are drawn trans- 

 verse to this axis, the general characteristics are well represented. It fails 

 also to give the relation of the displacement to the level of the sea except in 

 the case of the first line in the foreground. 



I am indebted to Mr. Gilbert for this method of illustration. 



