376 
successive capture of parts of it by different branches of the invading 
Muddy Fork. Fairly distinct sags in the ridges between the small sepa- 
‘ate systems strengthen this suggestion. If such a drainage adjustment 
ever took place, it has been so long ago that only these slight evidences of 
it remain. Such an adjustment would be possible, and if it did actually 
take place, it is probable the only case of its kind described. 
The first stream which still retains direct evidence of having once 
drained into the Blue River system is Dry Fork Branch. This stream now 
empties into Muddy Fork of Silver Creek, about a mile below Borden. It is 
the first of the series of barbed tributaries. In succession the tributaries 
of the old northwest drainage line were annexed to the Silver Creek sys- 
tem. A number of these, especially those coming in from the north, are 
decidedly barbed. The latest ones to be taken in were those in sections 
29 and 32, between Pekin and Borden. Evidence of this successive capture 
of the tributaries of the northwest extending stream is not found alone 
in the barbed drainage pattern. The gradation plain formed by the north- 
westerly flowing stream has not been entirely destroyed. To the northwest 
of Borden, just above the town, is preserved the oldest recognized portion 
of the old gradation plain. Quite a large remnant is preserved here, and it 
still retains the silts and gravels of the old stream bed. This remnant is 
shown beautifully on the topographic map. Fig. 1 shows its even line as 
quite a distinct feature where it has been cut into by the reversed drainage. 
The elevation of this ancient valley remnant is about 755 feet, whereas the 
present reversed valley floor is 575 feet in elevation. This means that the 
drainage change permitted the old gradation plain to be trenched at this 
place something like 180 feet. At the mouth of Dry Fork Branch the en- 
Fig. 1. 
plain of the former northwestwardly flowing stream just west of Borden. View taken 
from the south side of the present reversed valley. The present reversed stream is 
entrenched at this place 180 feet below the old gradation plain. The gradation 
ages renunene here has preserved upon it old gravels and silts similar to those shown 
in Fig. 5. 
View of the even surface (sky line) of a remnant of the old gradation 
