ProsseR.| Cretaceous. —Comanche Series of Kansas. 157 
No. 
J. Top of sandstone which is thought to represent the 
Big basin sandstone of Cragin. Thickness of sec- 
tion below this point not measured. 
A comparison of the three sections in the cafion region of Bluff 
creek indicates some variation in the thickness of the Kiowa shales. 
In the Amphitheatre section they have a thickness of fully 140 
feet. In the cne south of Hackberry creek, about five miles south of 
the Amphitheatre, the thickness of the same formation is approxi- 
mately the same or 135 feet; while in the section of Messing’s Bluff, 
about three miles east of the Hackberry section its thickness is only 
106 feet. In the latter section the top of the Red-Beds was clearly 
shown as also the base of the Tertiary, consequently there cannot 
be any considerable error in measurement. At the head of one of 
the southern branches of Hackberry creek toward its upper end is 
an interesting exposure of iron brown coarse sandstone similar to 
that which has generally been referred to the Dakota. This is one 
of the three prominent exposures of this sandstone seen in the 
rugged region of the northwestern central part of Clark county. 
In this vicinity decided breaks have been formed by the erosion 
from the general level of the high divide to the north, which sepa- 
rates the Arkansas river valley on the north from the tributaries 
of the Cimarron on the south. The bluffs thus formed are con- 
spicuously shown near the headwaters of Hackberry, East and 
West Bear and Little Sandy creeks. Near the top of these bluffs at 
the heads of Hackberry, West Branch Bear creek, and Little Sandy, 
are the three outcrops of the so-called Dakota sandstone. The one 
on Hackberry creek is about three miles southeast of the hamlet 
of Letitia on Section 21, Township 31 8., Range 28 W. At the head 
of the creek, from 20 to 25 feet of the brownish to iron colored 
sandstone is shown resting on the Kiowa shales. These shales in the 
upper part are very arenaceous and iron stained; but they contain 
Gryphacas and other fossils of the upper Kiowa. The top of the 
IKiowa shale is about 60 feet below the general level of the 
prairie in this vicinity. The prairie near the head of this 
creek is somewhat lower than the prairie near Letitia, the 
latter being 2540 feet above sea level. The hugh divide capped 
