72 ON THE GEOLOGY AND NATURAL HISTORY 
Although the group of beds observed along the Missouri river, near and below the 
mouth of the Judith, which we have referred provisionally to No. 1, has revealed many 
important facts to the geologist and paleontologist, yet the organic remains differ specifi- 
cally from those of any other formation with which we are acquainted in the Northwest, 
so that we are unable to fix with certainty its exact position in the geological scale. We 
are confident, however, that the fossils for the most part belong to Cretaceous types, 
although some of the remains seem to point to the Jurassic. We have, therefore, regarded 
these beds as Lower Cretaceous, though we have no evidence as yet that they are on a 
parallel with No. 1 as revealed along the Missouri below the Big Sioux. 
Having given the details of the geology of this group of beds in a memoir already pub- 
lished in the Transactions of this Society, I will not repeat them here in full, but in a sub- 
sequent chapter will present such additional information as I have been able to obtain. 
The following section will show approximately the lithological characters and order of 
succession of these deposits. The great disadvantage under which I labored and the hos- 
tile attitude of the Indians rendered it, much to my regret, impossible for me to examine 
this region over a large area to form a connected section of all the beds in detail. To 
attain so desirable a result will be the object of my exploration the coming season. 
SECTION OF THE OLDER Deposits AT THE MoutTH or JUDITH RIVER, IN DESCENDING ORDER. 
Feet. 
1. Yellowish and reddish rather coarse-grained sandstone, becoming deep red on exposure, containing Inoce- 
ramus ventricosus, Muctra alta, Cardium speciosum, &c. &e., . 9 . : . 0 - 20 to 25 
2. Mixed pure and impure lignite, whole bed containing many crystals of selenite and a yellowish substance 
like sulphur. The masses of lignite when broken reveal in considerable quantities small reddish erystal- 
line fragments of a substance having the taste and appearance of rosin, c c . : : 6 to 8 
8. Variable strata of drab clay and gray sand and sandstone. Upper part containing large numbers of Ostrea 
glabra. Near the middle there are gray or ash-colored clays with very hard bluish gray, granular, silici- 
ous concretions containing Hettangia Americana, Panopea occidentalis, Mactra formosa, &e. &e., 80 to 100 
A fine collection of fossils were obtained from these marine deposits, which will appear 
with the catalogue of Cretaceous species. Underlying these beds, where upheaved, were 
seen a series of variegated strata, clay, sands, &c., which undoubtedly are of Jurassic age. 
ForMATIOoN No. 2 of GENERAL SECTION. 
This formation is first revealed in thin outliers below the mouth of Big Sioux river, and 
on the Big Sioux six miles above its mouth, it caps the bluffs, apparently mingling to some 
extent with the succeeding bed, and containing at this locality large numbers of Jnoceramus 
problematicus and fragments of fishes. Near the mouth of Iowa creek and above, 1t shows 
