144 KANSAS ACADEMY OF SCIENCE. 
covered grassy slope is ordinarily indicative of a shale bed; and it is but neces- 
sary to notice how large a per cent. of the Dakota area is occupied by these 
covered slopes, in order to get a tolerably correct idea of the amount of shaly 
material contained in the group. It is because of the fact that the shale is 
covered that it has so persistently escaped notice. It should, perhaps, also be 
noticed in this connection that in many, perhaps most, cases these covered 
slopes are strewn with boulders and fragments of rock from the ledges above. 
These often give the slope the appearance of arocky ledge, when the underlying 
strata consist of shale and clay. 
Mr. Logan distinguishes two general groups in the Dakota: a lower or ferru- 
ginous group, and an upper or saliferous group. The upper group is divided 
into a lignite horizon, a salt-marsh horizon, and a gypsiferous horizon.*® It is 
not the understanding of the writer that Mr. Logan intended these as general 
divisions of the entire group, but rather for that part which he studied, viz., the 
area between the Smoky Hill and the Republican rivers. The conditions noted 
by Mr. Logan obtain for the region described by him, but are not characteristic 
of the entire group. Saliferous shales and lignites seem to be found rather more 
abundantly in the upper than in the lower beds; but even this statement must 
be considered general rather than specific. After four years spent in studying 
the various horizons, from Oklahoma to Minnesota, the writer is reluctantly 
forced to the conclusion that any persistent or general division of the Dakota 
group is not only impracticable, but, in the light of our present knowledge, im- 
possible. That he would prefer it otherwise will be apparent from the discussion 
of the flora of the group. In this connection a quotation from Doctor Lesque- 
reux seems pertinent: 
Le . The whole group bears, with scarcely any change in the nature and 
compound of its strata, the same essential character, from the lowest strata to the 
line of conjunction with the Fort Benton above it. . . . The compound is 
essentially the same in the whole thickness and in the whole extent, varying only 
in the degree of hardness, compactness, and red coloring resulting from the dif- 
ferent proportions of oxide of iron with which it is impregnated.’’” 
ORIGIN OF DEPOSITS. 
There has been no little diversity of opinion regarding the origin of the ma- 
terial, and especially the conditions incident to the deposition of the Dakota 
group. Professors Capellini and Marcou considered the formation a fresh-water 
deposit. This was due to the small proportion of calcium contained in the rock, 
as well as the general paucity of marine fossils. Meek and Hayden, who had 
better opportunities for observation, considered the beds marine; and in proof of 
their position cited the presence of a few marine invertebrates in the upper beds 
at Sioux City. 
The fossils found in Kansas in what are now known to be Lower Cretaceous 
horizons were also taken as evidence that the beds were of marine origin. Doctor 
White, on the contrary, was disposed to consider the group in general as non- 
marine. There are grave difficulties in either position. The extent of the group 
and the homogeneity of its constituent parts would seem to vitiate the theory of 
fresh-water origin. It is very unlikely that a fresh-water deposit would cover an 
area the size of the Dakota. On the other hand, the dicotyledonous flora, the 
absence of limestone and the extreme scarcity of marine shells throughout the 
greater part of the group preclude the idea of deep-sea deposits. Both of these 
views being untenable, another must be sought. 
48. Univ. Geol. Surv. of Kansas, 2: 297-209. 
49. Cretaceous Flora, p. 23. 
