462 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



the fact that we already know that there is in ISTebraska in clearly Cre- 

 taceous rocks, a flora that was referred by the highest European author- 

 ity to the Miocene. I do not know, however, how far Professor Les- 

 quereux's opinion that the Bitter Creek plants are Tertiary may rest 

 upon specific identifications among them of forms known to occur in 

 well determined Tertiary rocks elsewhere. 



TERTIAEY AGE. 



Bracliish- water beds of Bear Blver.* — In redemption of the promise 

 made, I now return to the consideration of the age of the brackish- water 

 beds 0f Bear Eiver, (division 28 of sec. — , on p. — .) These have al- 

 ways been regarded by me provisionally as Lower Eocene, not only 

 because their included fossil remains were closely related to forms^ 

 occurring in the Eocene lignite beds and deposits of the Paris Basin 

 and the mouth of the Ehone, but also because none of them belonged 

 to characteristic Cretaceous types. If, however, the beds of Bitter 

 Creek and the Judith Eiver should finally prove to be Cretaceous,, 

 the brackish-water beds in question must probably be relegated to the 

 same epoch, though they are not known to hold any species in common 

 with the Bitter Creek beds, and but one with those of Judith Eiver.. 

 Their approximate conformability with Cretaceous beds, indicating dis- 

 turbance and upheaval at the same time, favors this conclusion. I may 

 add that I have not been wholly without the suspicion that they might 

 prove to be Cretaceous, and in a report to Mr. Clarence King, published 

 in his report on the geological survey of the fortieth parallel, (vol. 3, p. 

 466,) I summed up my conclusions in the following terms : 



While I am therefore willing to admit that facts may yet be discovered that will warrant 

 the conclusion that some of these estuary beds, so widely distributed here, should be in- 

 cluded ratiier in the Cretaceous than in the Tertiary, it seems to me that such evidence 

 musfc either come from included vertebrate remains, or from further discoveries respect- 

 ing the stratigraphical position of these beds with relation to other established laori- 

 zons, since all the molluscan remains yet known frdm them (my own opinions are en- 

 tirely based on the latter) seem to point to a later origin. 



This paragraph has been misunderstood by Professor Cope,f who has 

 brought it into context with the statement respecting the age of the Bitter 

 Creek coal strata, and asserted that the nearest approximation to the 

 point of identification of the Bitter Creek strata with the Cretaceous 

 were thus made by myself, and conveyed the impression that no positive 

 reference had been made of any of the Bear Eiver beds to this period. 

 This, however, as has been shown elsewhere, had been done in the most 

 unequivocal manner with regard to the deposits of marine coal at Bear 

 Elver City, Wyoming, as well as at Coalville, Utah. 



I had intended to make more extended remarks on the several Ter- 

 tiary deposits referred to, and to have given lists of fossils from them, 

 but sudden illness, and the necessity for sending copy without further 

 delay to the Public Printes, have compelled the relinquishment for 

 the present of such design. 



* Until some decidedly Cretaceous fossils have been somewhere found in or above 

 these beds, they may be left in the lower Eocene. Our discovery of a group of fresh- 

 water shells as modern in appearance as these (though all different species) at Coal- 

 ville, far down in the Cretaceous, shows bow cautious we should be in deciding such, 

 questions. 



t Proceedings American Philosophical Society. Extras dated in MSS. February 7, 1873.. 



