THE CEEEKS CATACLINAL. 215 



inception of the uplift must therefore have been early in Tertiary time, and 

 the same evidence shows that by the middle of the Tertiary it was in great 

 part, if not entirely, completed. For unless the uplift had approached some- 

 where near its present dimensions the granite would not have stood suffi- 

 ciently high above the level of the Tertiary conglomerate to render the 

 transportation of its pebbles practicable. 



The evidence derived from the stratigraphy shows, then, that the upris- 

 ing of the Hills took place either wholly or in chief part during the interval 

 of time between the completion of the Cretaceous formation and the begin- 

 ning of the Miocene Tertiary. 



Further light upon the history of the displacement is thrown by the 

 drainage system. An attentive study of the arrangement of the streams shows 

 that in their relations to the rock structure they fall into two classes. The 

 first class includes all the creeks which drain the central area of the Hills. 

 The second includes the two rivers, branches of the Cheyenne, which flow 

 past the Hills and receive the waters of the creeks. With slight exception 

 the creeks flow in the direction of the dip of the strata, or, if we use the classi- 

 fication of Powell, are " cataclinal." Rising for the most part near the center 

 of the uplift, they run outward in all directions, just as the rocks dip out- 

 ward in all directions. If the dome of strata were formed under a lake or 

 sea and then laid bare by the recession of the water, it would be natural 

 that the drainage system created by the rain upon the rounded surface 

 should show a descent everywhere in the direction of the dip. If the top 

 of the uplift appeared above the water before the uprising was completed, 

 the result would be the same, and it would not be far different if the scene 

 of the uplift was a plain instead of a sea bed, provided the uprising was 

 not of exceeding slowness. In either case the arrangement of the drain- 

 age is a distinct consequence of the uprising and would be classed as "con- 

 sequent." It is difficult to conceive of any system of drainage except a 

 consequent system, in which all the streams are cataclinal, and it is there- 

 fore extremely probable that the creeks of the Hills acquired their positions 

 and directions either during the formation of the uplift or else when it was 

 laid bare by a retiring lake. In either case the drainage system is conse- 

 quent upon the uplift. 



