EPOCHS SEPARATING THE GROUPS. 67 



everywhere seen to rest upon a somewhat massive sandstone which is under- 

 laid by bad-land sandstones, shales, conglomerates, &c., with a somewhat 

 massive indurated sandstone at the bottom. There seems to be a very 

 decided change in the paleontology of these groups from base to summit, 

 but the fossils, so far as now known, do not afford definite lines of demar- 

 kation. 



The relation of these groups to those established by Professors Meek 

 and Hayden on the Upper Missouri is not well determined. I have care- 

 fully tried to use their system of grouping and have failed. A very 

 different lithologic series is observed, as must be apparent from a comparison 

 of the two sections. Most of the fossils are of different species, and the 

 few that can be referred to the species of Professors Meek and Hayden in 

 that region present contradictory evidence. Those fossils that may be 

 referred to "No. 2" are found above fossils which may be referred to " Nos. 

 3 and 4," and as we are tracing these bejds over broad areas, and from time 

 to time collecting new fossils, the stratigraphic relations of which should be 

 given with their description, it seemed necessary that some grouping 

 should be adopted, and I have given the best I could under the circum- 

 stances. Perhaps after -the paleontology is more thoroughly studied the 

 Upper Missouri groupings can be adopted here, but my present opinion is 

 that all such attempts will prove futile. These opinions are based chiefly 

 upon geological reasons, viz : All the evidence that has been published by 

 Dr. Hayden and members of his corps concerning the Park Province, and 

 all my own observations in that region, lead me to the conclusion that a long 

 chain of islands stretched in a northerly and southerly direction through 

 that region of country, separating the Cretaceous sea of the Plateau Prov- 

 ince from the Cretaceous sea of the Upper Missouri ; probably not forming 

 a continuous wall between fhe waters of the two, but separating them in 

 such a manner that very different physical conditions prevailed. It is mani- 

 fest that the Cretaceous sea of the Plateau Province was fed chiefly with 

 the sediments of the Basin Province, for all the- Cretaceous sediments rap- 

 idly attenuate from that old shore line eastward, and many conglomerates 

 and coarse sandstones of Cretaceous Age found there, are steadily replaced 

 by finer materials in an easterly direction. It is much more probable that 



