GEOLOGICAL SUEVEY OF THE TEERITORIES. 291 



however, nor any strictly marine forms above them, it is possible that 

 they may belong to the lower tertiary. 



From the affinities of some of these fossils to forms found in the latest 

 of the beds referred in California to the cretaceous, and the intimate 

 relations of these marine coal-bearing strata of Utah to the oldest ter- 

 tiary of the same region, and the apparent occurrence of equivalent 

 beds bearing the same relations to the oldest brackish- water tertiary 

 beds at the mouth of Judith Eiver on the Upper Missouri,* I am in- 

 clined to believe that these Coalville beds occupy a higher horizon in 

 the cretaceous than even the Fox Hills beds of the Upper Missouri cre- 

 taceous series; or, in other words, that they belong^) the closing or 

 latest member of the cretaceous. 



All of the explorers of this region concur in the statement that the 

 above-mentioned cretaceous beds are intimately related to the succeed- 

 ing brackish-water deposits that appear to belong to the oldest tertia&y ; 

 the two formations, wherever they occur together, being conformable 

 and without any intermediate beds, so that the one seems to shade into 

 the other, without any abrupt or sharply-defined line of separation ; the 

 change being mainly indicated by a gradual transition from beds con- 

 taining cretaceous types of only marine origin, to those with brackish 

 and fresh water types, apparently most nearly allied to early eocene spe- 

 cies of the Old World. 



So far as yet known, there would appear to be no strictly marine ter- 

 tiary deposits in all this interior region of the continent ; even the lower 

 parts of the surface here having been apparently gradually elevated 

 above the sea level at, or very near, the close of the cretaceous period. 

 For the same reason all of the beds hitherto referred with confidence to 

 the cretaceous are of undoubted marine origin, as they contain only 

 marine types. 



These cretaceous gulfs or seas, however, evidently did not occupy the 

 whole country here, as we know from the absence of cretaceous deposits 

 throughout what were doubtless wide areas, or possibly, in some cases, 

 smaller islands of dry land at that time. As the whole surface was 

 gradually elevated, however, even the lowest portions rose finally to 

 near the tide level, thus, probably, leaving large inlets and estuaries of 

 brackish waters that subsequently became so far isolated by the contin- 

 ued elevation, and from sedimentary deposits, as to prevent the influx 

 of the tides and form fresh-water lakes, in which the later fresh-water 

 and terrestrial types of fossils only were deposited. 



That this change from marine to brackish-water conditions was exactly 

 contemporaneous with the close of the cretaceous epoch, and the intro- 

 duction of the tertiary in Europe, is not certain ; nor is it necessary that 

 this should have been the case to constitute the older rock cretaceous and 

 the later tertiary, because in the use of these terms we have reference 

 rather to the order of succession of certain great physical changes, affect- 

 ing life in distantly-separated parts of the earth, than to the exact time 

 of the occurrence of these changes. 



* Associated with the estuary beds at the mouth of Judith Eiver, on the Upper Mis- 

 souri, there is a yellowish arenaceous rock, agreeing exactly in its lithological charac- 

 ters with the coal-bearing strata on Bear Eiver, in Utah, and containing an oyster ap- 

 parently belonging to the same species as one found in the rock mentioned at the lat- 

 ter locality. All of the strata at this Judith Eiver locality are upheaved, and more or 

 less mingled together, and I have long suspected that some vertebrate remains found 

 there by Dr. Hayden, and supposed by Dr. Leidy to be cretaceous types, belong rather 

 to the sandstone, that appears to be an equivalent of the Bear Eiver coal strata of 

 Utah, than to the estuary beds. It is even possible that equivalent beds at other 

 localities in the Upper Missouri country may have been, from the absence of charac- 

 teristic fossils, included along with the tertiary. 



