Abstract

The Paleozoic sequence of strata is well exposed in the northeast end of Glenwood canyon and near the junction of the Eagle and Colorado rivers. Although the formations are folded and faulted they have not been affected by mineralization here as in many other places where they have been studied. The Cambrian starts with a locally developed conglomerate of quartz pebbles resting on the weathered and eroded surface of the pre-Cambrian schist. This is succeeded by the Sawatch quartzite which contains one fossiliferous shale bed. The dolomites between the Sawatch quartzite and the Devonian Parting quartzite member are usually assigned to the Ordovician on account of their stratigraphic position. The dolomites occupying this position in the vicinity of Dotsero have yielded a fauna of upper Cambrian dendroid graptolites and are here named the Dotsero dolomite: These are overlain disconformably by the Devonian Chaffee formation which is subdivided into the Parting quartzite member and the Dyer dolomite member, separated by a weathered zone at the top of the Parting quartzite member. The Mississippian Leadville limestone rests disconformably on the Devonian. The thick upper bed is an oolite which is not characteristic elsewhere. The surface became pitted with sink holes before the deposition of the Pennsylvania strata. The latter are called the McCoy formation and exhibit abrupt lateral changes throughout their thickness. They pass upward without apparent break into gypsum and red beds which are tentatively assigned to the Maroon formation of the Permian. A comparison is made with the Pennsylvanian-Permian section at McCoy.

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