TWENTY-NINTH ANNUAL MEETING. 115 
four regions, and has been subjected to the most active erosive agencies, yet its 
systems of chert-bearing limestone have withstood the degrading influences to a 
wonderful extent. The Permian shales are practically homogeneous, so far as 
our purposes here are concerned. In this locality erosion has nearly completed 
its more active work. 
THe Rep BeEps. 
A section extending from Medicine Lodge in a southwesterly direction 
across the Salt Fork, Barber county, passes through a highly developed portion 
of the Red Beds. The elevated summits represent approximately the primal 
plain. 
The climate here is quite arid, and the streams are dry during the greater part 
of the year. Vegetation is sparse, especially at the heads of the arroyos. Far- 
ther down the streams vegetation becomes more abundant, and trees are quite 
common. On the hillsides the grass is so thin that the red earth may be seen for 
miles, even in the summer months. The lack of vegetation at the very heads of 
the streams, where it would retard degradation the most, makes the conditions 
most favorable for rapid erosion, and has probably played no unimportant part 
in determining the present topography of the region. Plate IV in the foreground 
shows the grass only in little bunches far apart, as is the general rule. In the 
upper part of this formation is a stratum of gypsum 25 feet in thickness. Under 
this are several hundred feet of soft arenaceous and argillaceous shales and sand- 
stones which seem to be much more easy to erode than the gypsum. The gyp- 
sum tends to preserve the original plain, while the rapidly-eroding shales form 
large, steep escarpments and the ‘‘ Mansard Buttes’’ of Professor Hay.* These 
are illustrated in plate V. The minor streams have not yet reached their base 
levels and are dry most of the year, corrading their beds only in times of flood, 
and producing the canon-like topography peculiar to these conditions. The 
greater streams have about reached their base levels and are beginning to widen 
their valleys. As a consequence, there is very little bottom land or high prairie, 
the country being simply a system of hills and sharp valleys. 
Notwithstanding the fact that there are many conditions favorable to erosion,. 
yet through the lack of perennial streams and springs and the uneven distribution 
of the rainfall in this locality, which comes within a short time in the spring, deg- 
radation seems to progress less rapidly than in some other parts of the state. The: 
Medicine Lodge river has cut a fairly wide valley through this formation, and is: 
not corrading its channel to a very great extent at present, but is wearing away 
its bluffs. Its bed is covered with ‘‘ quicksand,’’ over which flows a small stream 
of water. 
The Salt Fork flows, largely, in a small cafion in its course through Comanche 
and Barber counties. Its bed is covered with sand from the Tertiary formation 
at its head. The smaller streams flow in V-shaped valleys which are often quite 
deep, and at the heads of which are occasionally semicircular excavations with ver- 
tical walls sometimes 40 feet high. These places are sometimes several rods in 
diameter. On the ridges the ground is nearly level, and these depressions can- 
not be seen until approached within a few rods. Good examples of this form of 
an arroyo head may be seen a few miles southwest of Medicine Lodge and on the 
small tributaries to the north of the Salt Fork, in Comanche county. At the 
place where the Medicine Lodge river passes through the eastern limit of the 
gypsum, the gypsum weathers in little outliers between the main bluff and the 
river, forming round hills capped with gypsum. The side next the river is some- 
* Bull. No. 57, U. S. Geol. Surv. 
