This study was begun in 1925 with the help of loaned collections from various Jurassic localities in the Rocky Mountains and the Great Plains. At that time, it was the current notion that the Jurassic formation of that region was a deposit of one brief age, and containing only one fauna. From the study of the loaned collections it became evident to the author that neither of these suppositions was tenable. The evidence invited field work, which was begun in 1930, and more field work was done in the two years following. The results of most immediate interest are those connected with the Wyoming Jurassic, and they are, therefore, made the subject of this report. Under the heading, eastern Wyoming, is included a section in Fall River County, South Dakota, and the western Wyoming (Yellowstone) material includes sections from adjacent areas in Montana.


The Jurassic . . .

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