WHITE.! SURFACE GEOLOGY DRIFT. 55 



White River. — In no part of that portion of its course which lies ad- 

 jacent to this district, does White Eiver Valley afford so striking an 

 example of antecedent drainage as the valley of the Yampa does. 

 Nevertheless, the course of White Eiver is sufficiently independent of 

 the displacements of the strata over which it flows to show that it should 

 be properly placed in the same category in this respect, with the Yampa 

 and Green Kivers. 



Upon leaving Agency Park, White Eiver cuts through Grand Hog- 

 back, which crosses the valley at right angles; and from there west- 

 ward to the southern end of Piiion Eidge, a distance of between 25 and 

 30 miles, it runs in large part upon the yielding strata of the Wasatch 

 Group, and in part upon the lower strata of the Green Eiver Group. It 

 then runs for a few miles among the strata of the Fox Hills and Lara- 

 mie groups, where they are upturned by the Midland Flexure. It then 

 returns to the Wasatch Group again, upon which it runs nearly to Eaven 

 Park, where it crosses in both the descending and ascending order, the 

 Laramie, Fox Hills, and Colorado groups. After passing the Eaven 

 Eidge Flexure at the western side of Eaven Park, the river again flows 

 five or six miles upon the strata of the Wasatch Group, and then enters 

 a caiion which it has carved out of the strata of the Green Eiver Group, 

 nearly all the way to its confluence with Green Eiver. This caiion 

 is from COO to 1,000 feet deep, from the adjacent upland surface; and 

 although it is narrow, its sides are not usually so precipitous as those 

 of Yampa Caiion are. 



Throughout a large part of the course of White Eiver, there is appar- 

 ently no special condition of the underlying strata that might be sui)- 

 posed to have governed its direction so far as lateral deflection is con- 

 cerned ; but its direction seems to have been just as little influenced 

 by the abrupt flexures the strata have suffered over which it flows near 

 Pinon Eidge and at Eaven Park. 



Milli Creek. — The upper branches of Milk Creek flow in such a man- 

 ner and have such relations to the underlying strata as any kind of 

 drainage, either antecedent or consequent, might have. But from the 

 point at the north side of Axial Basin, where these branches coalesce, 

 the creek, instead of continuing down the low land of the open basin, 

 as one might expect it to have done, turns abruptly northward through 

 a caiion, or very narrow valley, three miles long and 800 feet maximum 

 depth, which it has carved out of the strata of the Fox Hills Group, and 

 joins the Yampa which there runs in a similar canon. 



No other theory than that of antecedent drainage, seems at all ade- 

 quate to explain the extraordinary course of such a creek. It is, how- 

 ever, most remarkable that a creek so small as this could have such a 

 history — a history that dates back to a time before the great mountains 

 near by were made, and before the grand lineaments which the conti- 

 nent now bears were carved. 



SCATTERED DRIFT. 



No considerable portion of the surface of the region adjoining the 

 Eocky and Uinta Mountains is free from well-worn scattered drift- 

 pebbles. These pebbles are composed of various kinds of rock, but 

 they are largely quartzites of various colors, and are usually as smoothly 

 rounded as any that are now washed upon a storm-beaten sea-shore. 



To one who is familiar with the great northern glacial drift, these 

 pebbles suggest the same or a similar history ; and when we attempt to 

 trace their origin by comparing their lithological compositipu with that 



