OF THE UPPER MISSOURI. 53 
number of thin layers and beds; and secondly, the frequent repetition of similar beds at 
various horizons. Again, the almost entire absence of heavy massive strata of limestone, 
or other hard material possessing sufficient durability to form perpendicular escarpments 
of much extent, is worthy of note. As a general thing, the limestones vary from only a 
few inches in thickness, to from one to three or four feet, and rarely, as in Nos. 14 and 18, 
attain a thickness of from thirty-eight to forty feet. Although various light-colored lami- 
nated clays and soft argillaceous shaly beds predominate, and arenaceous material is not 
unfrequently present, it is somewhat remarkable that dark bituminous shales and beds of 
coal are rarely met with, even among the outcrops seen along the Kansas, below the mouth 
of Blue river, belonging to the upper Coal measures, and holding a position below the base 
of the foregoing general section ; while through a considerable thickness of beds belonging 
to higher portions of the Coal measures included in the lower part of this section, as well 
as through the strata containing Permian fossils above, beds of coal and dark carbonaceous 
shales appear to be almost, if not entirely wanting. 
It will be observed we have in this general section, without attempting to draw lines 
between the systems or great primary divisions, presented in regular succession the various 
beds with the fossils found in each, from the Cretaceous sandstone on the summits of the 
Smoky hills, down through several hundred feet of intermediate doubtful strata, so as to 
include the beds containing Permian types of fossils, and a considerable thickness of rocks 
in which we find great numbers of upper Coal measure forms. We have preferred to give 
the section in this form because, in the first place, the upper Coal measures of this region 
pass by such imperceptible gradations into the Permian above, that it is very difficult to 
determine, with our present information, at what particular horizon we should draw the 
line between them, while, on the other hand, it is equally difficult to define the limits 
between the Permian and beds above, in which we found no fossils. 
Beginning near the base of this section, we find we have in great numbers the following 
well-known and widely distributed Coal measure fossils, viz.: Fusulina cylindrica,* Cho- 
netes Verneuiliana, Productus splendens (or a closely allied species), Retzia Mormonit, Rhyn- 
chonella Uta, Spirigera subtilitau, Spirifer cameratus, S. planoconrexa, and a EHuomphalus 
similar to #. rugosus of the Coal measures, while the few new and undetermined species 
associated with these are, for the most part, also decidedly more nearly allied to Carboni- 
ferous than Permian forms. We should here remark, however, that we occasionally met 
with a species of Monotis, allied to the Permian species IZ Speluncaria and Synocladia 
biserialis, also regarded in the Old World as a Permian genus, at horizons far beneath the 
* Tn Russia, Fusulina cylindrica is said to occur only in the upper part of the lower Carboniferous series; but 
the fossil generally referred to that species in this country appears to be confined to the Coal measures. We have 
some doubts in regard to its identity with the Russian species. 
