Davis and Wood.] 
410 
[Nov. 20, 
remnant of the former river could have cut so deep a gap in the 
front ridge. It is possible, however, that the inequality of depth is 
only apparent, and is really due to a heavy drift filling in the wind 
gap of the second ridge, where the moraine crosses it. This seems 
very likely. 
Inequality of thickness in the lava sheets does not appear clearly 
in First and Second mountains, but it is probably characteris- 
tic of the third sheet, which is thinner than the others, and is worn 
down low in part of its length, so low as to suggest structural weak- 
ness rather than concentration of destructive processes. Its sev- 
eral parts have different local names ; Long hill, Kilters’ hill and 
Hook mountain. 
The conception of the Highland plateau, as an old baselevel 
plain, elevated and partly cut away again, may now be recalled once 
more. Returning to one of the high points of view on the front of 
the Highlands, and in imagination filling up again the Highland 
valleys and the Triassic lowlands to the general level of the crys- 
talline plateaus and trap ridges as described in paragraph 15, we 
must now stretch the Cretaceous cover over the Triassic area to 
the margin of the crystalline Highland plain, a cover formed of ma- 
terials washed from the inner non-submerged portion of the High- 
lands. From this as the initial condition of the Somerville cycle, 
the greater part of our existing geography appears to be developed. 
30. Drainage of the Uinta Mountains of Utah. It thus appears 
that while the present Watchung drainage is in greatest part ac- 
cordant with the structure of the district, it is also in a small way 
characterized by such significant discordances that its origin is best 
referred to superimposition. As a corollary of this, it follows that 
superimposed drainage is to be recognized by its full discordance with 
structure only during its youth, and that in its more mature age it 
may come to be almost or fully accordant, thus simulating conse- 
quent drainage. Antecedent drainage may in the same way lose its 
initial discordances. With this in mind, we have looked over Powell’s 
account of the drainage of the Uinta mountains, where he first pro- 
posed the terms antecedent, consequent and superimposed, 1 the idea 
embraced in the latter term having been previously stated by Mar- 
vine. 2 The drainage of the Uinta mountains is concluded to be 
chiefly antecedent ; not only the Green river being thus regarded, 
1 Expl . Colorado River of the West, 1875, 163, 166. Geology of the Uinta mountains, 
1876. 12. 
2 Hayden’s Surveys, Report for 1873 [1874), 144. 
