Abstract

The section of the Morrison formation recommended as the “type” has been selected because the entire Morrison is exposed along the West Alameda Parkway road cut, 2 miles north from Morrison, Colorado, and because the locality is readily accessible.

The Morrison formation at the recommended type section is a distinct cartographic unit which can be subdivided into six parts primarily on the basis of lithologic characteristics of the sedimentary rocks.

Fossils in this section of the Morrison formation are confined to three horizons. Dinosaur remains occur in limited number in basal sandstones of the gray shale and sandstone unit. Probable fresh-water sponge spicules are plentiful throughout an interval of 25 feet in the central part of the gray clay and limestone unit. A few spicules, however, are also present from 2 to 6 feet above the dinosaur-bearing sandstone. Aclistochara, the occurrence of which has not been mentioned previously in literature on the Morrison formation in Colorado, is relatively abundant in the upper 30 feet of the gray and red shale unit. This would place the highest occurrence of Aclistochara 63 feet above the base of the Morrison formation.

The results of copper nitrate staining of samples from the calcareous rocks of the Morrison formation indicate that the greatest amount of calcite is present in the gray clay and limestone unit. In all probability the distribution and intensity of copper nitrate stains could be used effectively in connection with petrographic studies to identify several strata within the formation.

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