1856.] > 267 



perhaps identical with our F. bticcinoides, both of which were at first only met 

 with in the bed of No. 5, likewise occur in No. 4. From these facts, we are in- 

 clined to regard these two rocks as only well marked subordinate members of 

 the same natural group, which is of the age of the true chalk. 



Too few fossils have yet been found in No. 2 and No. 3 to settle very definite- 

 ly their position in the Cretaceous system, though the late discovery by one of 

 us* of Inoceramiis problematicus, near the base of the first, appears to show that 

 this bed is not, at any rate, older than the upper Green Sand, and that it may 

 also belong to the chalk. 



In our section of the Nebraska formations, given in a paper published in the 

 8th vol. of the Proceedings of the Academy, page 63, it will be remembered we 

 placed provisionally the beds of sandstone and clay composing formation No. 1, 

 seen at the mouth of Big Sioux river and below there, along with the Cretace- 

 ous strata, stating at the same time that they were not positively known to 

 belong to that system. We still think it barely possible these beds may be 

 older than Cretaceous, though if represented, as we think they are, by similar 

 beds seen holding about the same position near the mouth of Judith river, far up 

 towards the sources of the Missouri, we must either refer them to the Cretaceous 

 system, or admit the introduction of the genus Baculiies before that epoch, as we 

 have fragments of a small species of that genus from the Judith river beds. 

 At the same time it should be borne in mind that these strata at the last named 

 locality are characterized by a group of fossils remarkably distinct from those in 

 the rocks above, and that one species belongs to the genus Hettangia, a type of 

 bivalves, not known to occur, in the old world, in more modern formations than 

 those of the age of the Lias. If not older than Cretaceous, we think, from these 

 facts, as well as from the stratigraphical position of these beds, they probably 

 represent some of the older members of that system. What relation they bear 

 to the formations near the same locality, in which the saurian remains were 

 found, supposed by Prof. Leidy to be allied to the genera Iguanodon and Mega- 

 losaurus, is still an unsettled question. 



Should these Big Sioux and Judith river formations prove to be Jurassic, or 

 even to represent both the Jurassic and Triassic systems, it would not conflict 

 with the statement made by us in our last paper, that Mr. Marcou was mistaken 

 in coloring as Triassic and Jurassic the immense extent of country referred to 

 by us between these two localities, as we know this great area to be wholly 

 occupied by well marked Cretaceous and Tertiary strata, while the above 

 named doubtful beds, no whei;e come to the surface near the Missouri, between 

 these two widely separated localities, excepting for a short distance below the 

 mouth of Judith river. 



It would, perhaps, be premature to attempt, at the present time, the task of 

 tracing out in much detail the parallelism of the various members of the Cre- 

 taceous system in Nebraska, with those of New Jersey and other well known 

 districts in the States, or with those of the south western Territories ; yet the 

 occurrence of several of the more common and characteristic fossils of the upper 

 two Nebraska formations, such as Ammonites placenta, Scaphites Conradi, Bacu- 

 lites ovatus, Nautilus Dekayi, ^c, in the first and second Green Sand beds and 

 intervening ferruginous stratum of New Jersey,f as well as in the "Kotten Lime- 

 stone" of Alabama, clearly indicates the synchronism of these deposits, notwith- 

 standing their widely separated geographical positions. 



At the same time the total absence of the above named fossils, and indeed so 

 far as we yet know, of all the other species of the lowest and upper two Nebraska 

 Cretaceous formations, in the rocks from which Roemer and others collected so 

 many species in Texas, and other south western localities, renders it highly pro- 

 bable that if the latter occur at all in Nebraska they must be represented by 



* Dr. Hayden. 



f For our knowledge of the geological positions of these fossils in New 

 Jersey, we are indebted to Prof. Geo. H. Cook, of the geological survey of that 

 State. 



