thin-bedded; Range and Gros marine. Ventre Mountains. Gros Ventre 600-800 Shale, green, North and west Formation flaky, with Death flanks of Teton Canyon Limestone Range and Gros Member composed of Ventre Mountains. about 300 feet of hard cliff-forming limestone in middle; marine. Flathead 175-200 Sandstone, North and west Sandstone reddish-brown, flanks of Teton very hard, Range and Gros brittle; partly Ventre Mountains. marine. The regularity and parallel relations of the layers in well-exposed sections such as the one in Alaska Basin suggest that all these rocks were deposited in a single uninterrupted sequence. However, the fossils and regional distribution of the rock units show that this is not really the case. The incomplete nature of this record becomes apparent if we plot the ages of the various formations on the absolute geologic time scale (fig. 34). The length of time from the beginning of the Cambrian Period to the end of the Mississippian Period is about 285 million years. The strata in Alaska Basin are a record of approximately 120 million years. More than half of the pages in the geologic story are missing even though, compared with most other areas, the book as a whole is remarkably complete! During these unrecorded intervals of time either no sediments were deposited in the area of the Teton Range or, if deposited, they were removed by erosion. [Illustration: Figure 32. _Paleozoic marine sedimentary rocks near south boundary of Grand Teton National Park. View is south from top of Teton Village tram. National Park Service photo by W. E. Dilley and R. A. Mebane._] Madison Limestone Darby Formation Bighorn Dolomite Gallatin Limestone Advance and retreat of Cambrian seas: an example