94 Cretaceous. 



These Cretaceous gulfs or seas, however, evidently did notoccup}^ the 

 whole couutry here, as we know from the absence of Cretaceous de- 

 posits 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 eytuaries 

 of brackisli waters, that subsequently became so far isolated, by the 

 continued 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 tj^pes of fossils only were deposited. 



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

 actly contemporaneous with the close of the Cretaceous epoch, and the 

 introduction of the Tertiary in Europe, is not certain ; nor is it neces- 

 sary 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, affecting life in distantl}^ separated parts of the 

 earth, than to the exact time of the occurrence of these changes. 



He described from Bear river, near Sulphur creek (now Laramie 

 Group), Goniohasis chrysalis. 



From the Dakota Group, tiyelve miles southwest of Salina, Kansas, 

 (Jrassatellina oblonga, Area parallela, Yoldia microdonta, Corhicula 

 nucalis, C. siibtrigonalis, Cardium salinaense, C. kansasense, Arco- 

 jjagella mactroides, Tellina suhscitula, Leptosolen conradi, Turritella 

 kansasensis, and Turbo miidgeanus. From opposite Sioux Cit}^, in 

 Dakota county, Nebraska, JJnio nehrascensis. 



From the Fort Pierre Group, near Medicine Bow Station, Union 

 Pacific Railroad, Inoceramus altus. From the Fox Hills Group, at 

 the mouth of Deer creek, on North Platte, in Wyoming, To^jes tvyoraing- 

 ensis. From Box Elder and Colorado City, Colorado, Anisomyon 

 centrale. 



From the Fort Benton Group, at Oil Springs, twenty miles west of 

 Fort Bridger, Wyoming, Cardium pauper culum; from Point of Rocks,* 

 Wyoming, Anomia gryphhorhynchus. 



From Salt Lake, Utah, Pachymya truncata; and from Canon City, 

 Mactra canonensis. 



Wm. M. Gabbf described, from Chihuahua, Mexico, Lima kimballi. 



Alfred R. C. Selwyn]; described the Jackass mountain Conglomerate 



* Hayden's 5th Rep. U. S. Geo. Sur. Terr, 

 t Proc. Acad. Nat. Sci. 

 Geo Sur. Canada. 



