Chap. IY. GEOLOGICAL REMARKS. 247 
west extends along the Arkansas river as the northern 
boundary of its valley, and the road runs along at the foot 
of this plateau until it crosses the river above Fort Atkin- 
son. The characteristic features of this plateau are the 
small rocks on Walnut Creek, at Pawnee Rock and 
Pawnee Fork, and on the so-called Caches ; and the 
geological phenomena of these are repeated on the north 
side of the Cimarron, on the so-called Lower and Middle 
Springs. The conglomerate which appears here (clearly 
a higher stratum of the new red sandstone than that which 
furnishes the masses of quicksand on the Arkansas and 
Cimarron) is loosely held together by a white, powdery, or 
rather flour-like cement, and contains boulders of quartz, 
jasper, cornelian, flint, granite, syenite, trap, red, brown, 
black and green lava, scoriae, and brown pitchstone. 
Wherever the cement occurs in layers without boulders, 
a number of indistinct formations of organic origin are 
visible in the wbite mealy mass, which deserve to be 
examined under the microscope. The more distinct forms 
have the appearance of delicate roots and twigs, and in the 
fractures numerous small holes, like little tubes, are seen in 
many places. Here and there this net-work of organic 
remains is very hard, being penetrated by hydrated oxide 
of iron. A harder stratum forms the surface of these rocks, 
protects them against decomposition, and is the cause of the 
formation of this plateau. At Walnut Creek, Pawnee 
Rock and Pawnee Fork, this roof presents peculiar dark- 
brown masses, looking like half-fused sandstone, and as if 
they had formerly composed the surface of contact between 
the sandstone and a layer of lava which had flowed over it. 
Wislicenus asserts that these formations are of volcanic 
origin ; and on the Rabbit's Ears and the Round Mound, 
volcanic mountains on the sources of the Nutria or 
