ARKANSAS TERTIARY BASIN. 109 
were constantly passing over rocks which are nearly as soft and homogeneous as the variegated 
marls of the Painted Desert, but they have been affected by the erosive action they have suf- 
fered in a strikingly different manner. Instead of vertical sections of many hundred feet in 
height never absent from our sight, here were rounded hills and broad valleys, of which the 
smooth and grassy slopes revealed nothing of their rocky frame-work. Occasionally along the 
Cimarron the harder Cretaceous rocks break through the monotonous surface; but, aside 
from that, the views we had of the geological formation are comparatively few and superficial. 
Wherever seen, however, with the exceptions already made, we found the substrata to have a 
common character; and our observations would indicate the prevalence of rocks of one geological 
age over all this interval. 
These are soft, white limestones, either tufaceous and concretionary, or fine and chalky. 
They are generally in their beds, but in some instances are massive and somewhat sandy. So 
far as observed, these contained no fossils in the localities where we examined them. 
Till these strata can be more carefully studied, and fossils found in them, any conclusion in 
reference to their age must be liable to error. There is, however, little doubt in my own mind 
that they are Tertiary, and continuous with, or equivalent to, Tertiary strata which have been 
identified as such at various points north and west of this crossing of the Arkansas, They 
rest upon the Cretaceous rocks, generally on the Lower Cretaceous sandstones, and may be por- 
tions of the same formation; but their aspect is rather that of fresh-water deposits, and unlike 
any Cretaceous strata which have come under my observation in any country. Their lithological 
characters are precisely those of the Tertiary rocks of Nebraska, so fully explored by Dr. 
Hayden, as well as of the strata noticed in the descriptions of the geology of the Moqui 
country. I am also inclined to class with them the white tufaceous limestones of the Rio 
Grande valley. The conjecture that they are Tertiary is strengthened by the fact that Tertiary 
fossils were found by Colonel Emory (op. cit., p. 12) a little higher up the Arkansas than 
where we crossed it, in strata of somewhat similar character. I think it highly probable that 
future explorations will not only prove the area between the crossing of the Cimarron and 
Pawnee Fork to be part of a great Tertiary basin, but show that it stretches far away to the 
north, approaching, if not joining, the basin of White river. The high table-lands which sep- 
arate the valleys of the tributaries of the Arkansas are portions of a once continuous plateau 
which occupied all this region. The soil is good, and they are covered by a thick mat of most 
nutritious grass, (Buffalo grass, Sesleria dactyloides;) but the amount of rain which falls here is 
too small to admit of cropping the ground. The bottom lands of the Arkansas may, however, 
be successfully cultivated. Containing these different surfaces, this region is peculiarly 
adapted to grazing, and will doubtless soon be covered with domesticated flocks and herds in 
place of the bands of buffalo which now roam over it. 
PAWNEE FORK TO COUNCIL GROVE. 
Cretaceous formation.—As we descended from the high divide crossed by the ‘‘dry road’’ 
we left the Tertiary limestones behind us, and on the banks of Pawnee Fork came again into 
the reddish-yellow Cretaceous sandstones which we had last seen on the Upper Cimarron. 
They are best exposed on the banks of Pawnee Fork, a few miles further east. We could 
not determine with accuracy the easterm limits of this formation, as after passing Pawnee rock 
the underlying strata are entirely concealed for many miles. It is probable, however, that it 
does not reach beyond Walnut creek, for the consistence of the rock which represents it is 
such that it would be likely to make its appearance above the surface did it exist there. 
The sandstone composing Pawnee rock is reddish-brown in color, soft and coarse, much like 
that forming the base of the Cretaceous system at Smoky Hill, (sixty miles northeast, ) from 
which Messrs. Meek and Hayden have obtained a very interesting suite of Angiosperm-dicoty- 
