380 
Silver Creek system. The small wash from the north now sends its water 
into both systems. The rapid headward erosion of the new system will 
soon cause all of it to be deflected to the southeast. Likewise, the remain- 
ing tributaries of the old system must be taken over into the new system. 
Muddy Fork of Blue River would normally remain at its present elevation 
for a long period. In the meantime, the new system will invade farther and 
farther to the northwest, and in a short time, geologically speaking, Muddy 
Fork of Blue River itself will be taken over into the Silver Creek system. 
The headward erosion of the invading system will be relatively rapid, since 
it has mainly alluvium to work upon in order to capture Blue River. One 
might go still further in anticipation of this successive piracy. The invad- 
ing system will extend itself in the direction of the present flow of Muddy 
Fork of Blue River and capture tributary after tributary of the present 
stream, just as it has done in the past after capturing Dry Fork Branch of 
the old system. By following the line of a graded stream in this manner, 
the successive stream piracy must be relatively rapid. Such successive 
stream piracy will continue as long as the stream gradient in the reversed 
direction is more favorable for headward erosion than the normal present 
direction. Whenever these stream gradients reach a balanced condition 
the adjustment is complete and the drainage systems have arrived at the 
beginning of the old age condition. 
Development of Special Bed-Rock Terraces. 
Another result of the above described stream adjustments must be men- 
tioned in this paper. The barbed tributaries of Muddy Fork of Silver 
Creek have been adjusting themselves to a direction of flow in accord with 
that of the main stream where they enter it. They have a tendency to 
adjust themselves in such a manner that the junction of the main stream 
and the tributary form an acute angle pointing in the down stream direc- 
tion. Practically all of the barbed tributaries have been and are making 
this adjustment. Those on the north of the main stream have much more 
perceptibly oriented themselves in the down stream direction than those on 
the south. This is because the dip of the reck favors a migration of the 
main stream against the south bluff, especially in the non-graded portion of 
the valley. “This has resulted in a shortening of the tributaries from the 
mouth and the consequent nullification of their orientation in the down- 
stream direction of the mainstream. While this direction adjustment of the 
barbed tributaries has been taking place, the valleys have also been deep- 
ened by down cutting. The combination of this direction adjustment at the 
mouth of the tributaries and the down cutting has permitted bed-rock 
benches or terraces to come into existence on the upstream side near the 
mouths of the tributaries. (See Fig. 6.) Some of the tributaries have 
more than the one set of terraces. They range in height from 10 to 25 feet 
above the present valley flat or above one another. It is probable that new 
accession of drainage due to capture above has had something to do with 
the development of these bed-rock terraces, since the resulting more vigor- 
