tionable Cretaceous strata, in a district where the undisturbed 
condition of all the rocks precluded the supposition that there 
might have been an overthrow, settled the question that itcould — 
not be newer. i 
Soon after Dr. Newberry’s return, a letter was received from 
Professor Heer, who was evidently deceived by the unusually 
modern affinities of the leaves (and doubtless, though ur 
consciously to himself, in some degree by the theoretical views 
of Mr. Marcou, who was then in Zurich), stating that he could 
not regard these leaves of Cretaceous age, but that they appeared 
against them as weighty an authority as Prof. Heer, they 
tinued to maintain that the rock is, nevertheless, Cretaceous. — 
After having expressed so many and such widely different 
opinions in regard to the age of this formation, we may readily) 
understand that it must have been with no ordinary degree 
5 
_ There are a few points, however, in regard to this oro 
upon which the writer cannot agree with Mr. Marcou. 1). 
first place, he (Mr. Marcou) considers it a fresh-water forma 
because he found in it shells of a Cyrena; (for which he P 
poses the name C! Nova-Mezicana, from the supposition 4° 
AMentical with a species found by him in New Mexico). | h 
- undoubtedly the Cyrena arenaria of Meek & Hayden,’ ¥ 
Was long since described from the same locality and positio® 
nee there, however, by no means proves this to be ‘irecllf 
Aeposit, since the writer and Dr. Hayden found - | 
it as a Cyprina, from imperfect specimens, but 
geuus Cyrene yprina, pe pe 
= 
