114 



[June, 



forms ; while the sea was gradually becoming more shallow, as is shown by the 

 increase of gasteropoda. We even know from the presence of a few remains of 

 lycopodiaceous plants, and an occasional unbroken leaf of some exogenous tree, 

 that there was dry land at this time somewhere not very far away. Gradually, 

 as we ascend in the series, the strictly marine animals disappear, and we meet 

 with Ostrea, Corbula, and Ceriihium, mingled in the same bed with Mclania, Palu- 

 dina, Physa, Cyrena^ &c., all of Tertiary types; while a little higher in the 

 series, we find at some places only the remains of land and fresh water mollusca. 

 From the above facts, especially the presence of Pleurotoma, Fasciolaria, and 

 Belemnitclla, in this upper member of the Cretaceous system of this country, 

 we cannot think it represents any part of the Green Sand of English geologists. 

 Numerous well marked Cretaceous forms show it cannot be Tertiary, conse- 

 quently we think it must represent some portion of the true Chalk. We are by 

 no means inclined, however, to adopt the views of M. Alcide D'Orbiguy, 

 who regards all the Cretaceous formations of the United States and Western 

 Territories as referable to a later epoch than the Green Sand, as the next suc- 

 ceeding formation below that of which we have just been speaking, (No. 4 of 

 the series), is characterized by numerous fossils of unquestionable Green Sand 

 type. We think confusion has been created in tracing out the parallelism be- 

 tween American and European Cretaceous formations, by fossils from different 

 positions in this country having been mingled together and described as if they 

 occurred in the same bed. 



Formations at the base of the Cretaceous Scries of this district. 



As previously stated, near the mouth of Milk river, Cretaceous strata which 

 are not seen for a long distance below this on the Missouri, again rise to vievi'. 

 They consist of the upper two members of the series (No. 5 and No. 4) which, 

 in consequence of their inclination to the east, are found to rise higher and 

 higher as we ascend the river, so that nearly all the hills close to the Missouri, 

 between Milk and Muscleshell rivers, consist of these formations. Some four or 

 five miles below the mouth of Muscleshell river, a lower rock, a sandstone, 

 rises above the water level. This is probably No. 1 of the series. No. 2 and No. 

 3 not being represented here. It is worthy of note that out of two species of 

 Mactra^ two of Tellina, two of Inoceramus, one of Pholodomya, two of Nat/ca, and 

 one Bacuiite, found in this rock, not one is known to occur in any of the higher 

 formations, and some of these species are not unlike Neocomicn forms. 



In consequence of the increasing inclination of the strata, this last mentioned 

 sandstone rises in the vicinity of North Mountain river as much as 250 feet above 

 the Missouri. Here, or near this, begins a wild and desolate region, known as 

 the Mauvaises Torres or Bad Lands of the Judith. At various places in these Bad 

 Lands a sandstone similar to No. 1 was seen alternating with beds of clay and 

 lignite, all of which are upheaved and much distorted. It was found impossible 

 to devote to the examination of these formations time enough to determinetheir 

 relations to the Cretaceous and Tertiary strata of this region, without running 

 the risk of being cut off from the party and murdered by the Indians. Amongst 

 a few fossils that were collected here, however, Prof. Leidy finds teeth which 

 he refers to two or three genera of large Saurians allied to the Iguanodon, 

 Megalosaurus, &c. There arc also in the collection from some of these beds, one 

 or two species of Unio, one or more of Cyclas or Cyrcna, and a few crushed 

 specimens of Gasteropoda like Paludina and Mclania. From these facts, we are 

 strongly inclined to think with Prof. Leidy, there may be here, at the ba.' e of the 

 Cretaceous System, a fresh water formation like the Wealden. In as much, how- 

 ever, as there certainly are some outliers of fresh water Tertiary in these Bad 

 Lands, we would suggest that it is barely possible these remains may belong to 

 that ei)och, though the shells appear to be all distinct species from those found 

 in the Tertiary at all the other localities in this region. 



We remember seeing in 1853, between the mouth of Big Sioux and Piatt 

 rivers on the Missouri, some exposures very similar to those of the Bad Lands 

 of the Judith, excepting that there appeared to be no beds of Lignite. We saw 



