The Cretaceous of the Rocky Mountains was clearly developed by F. V. Hayden in 1855–1888 and by F. B. Meek (1857–1876). Other workers in this field were Charles A. White (1869–1891), and R. P. Whitfield (1877–1889). Since 1891 T. W. Stanton has been actively interpreting its stratigraphy and faunas. _Cretaceous and Comanche of Texas._—The broader outlines of the Cretaceous of Texas had been described by Ferdinand Roemer in 1852 in his good work, Kreidebildungen von Texas, but it was not until 1887 that Robert T. Hill showed in the Journal (=33=, 291) that it included two great series, the Gulf series, or what we now call Upper Cretaceous, and a new one, the Comanche series. This was a very important step in the right direction. Since then the Comanche series has been regarded by some stratigraphers as of period value, while others call it Lower Cretaceous; the rest of the Texas Cretaceous is divided by Hill into Middle and Upper Cretaceous. On the other hand, Lower Cretaceous strata had been proved even earlier in the state of California, for here in 1869 W. M. Gabb (1839–1878) and J. D. Whitney (1819–1896) had defined their Shasta group, which was wholly distinct faunally from the Comanche of Texas and the southern part of the Great Plains country. _Jurassic and Triassic of the West._—In 1864, the Geological Survey of California proved the presence of marine Upper Triassic in that State, and since then it has been shown that not only is all of the Triassic present in Idaho (where it has been known since 1877), Oregon, Nevada, and California, but that the Upper Triassic is of very wide distribution throughout western North America. Jurassic strata, on the other hand, were not shown to be present in California until 1885, while in the Rocky Mountain area of the United States there was long known an unresolved series of “Red Beds” situated between the Carboniferous and Cretaceous. This gave rise to the “Red Bed problem,” the history of which is given by C. A. White in the Journal (=17=, 214, 1879). In 1869, F. V. Hayden announced the discovery of marine Jurassic fossils in this series, and since then they have come to be known as the Sundance fauna, extending from southern Utah and Colorado into Alaska. Above lie the dinosaur-bearing fresh-water deposits, since 1894 known as the Morrison beds. In 1896, O. C. Marsh (1831–1899) announced the presence of Jurassic fresh-water strata along the Atlantic coast (=2=, 433), but to-day only a small part of them are regarded as of the age of the Morrison, while the far greater part are referred to the Comanche or Lower Cretaceous. The red beds below the Jurassic of the Rocky Mountain area have during the past twenty years been shown to be in part of Upper Triassic age and of fresh-water origin, while the greater lower part is connected with the Carboniferous series and is made up of brackish— and fresh-water deposits of probable Permian time.