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'' ' shales. Numerous thin but laterally continuous bentonite layers are found throughout the formation. The lower, middle and upper ' parts are often referred to as the Graneros Shale, the Greenhorn Limestone, and the Carlile Shale, respectively. The Codell Sandstone is the uppermost unit in the Ft. Benton Formation. In the Dowe Flats area, it has a 15-foot total 1 thickness and can be divided into a 7-foot gray siltstone beneath an 8-foot thick silty sandstone. This silty sandstone directly underlies the Niobrara Formation. ' The Niobrara Formation is traditionally separated into two units, the Fort Hays and Smoky Hill members. The Fort Hays Member ' is an extremely fine-grained, light gray limestone with thin interbedded shales. A section of Fort Hays Member at the south end ' of Dowe Flats measured 16.5 feet thick (Lowman 1977). Limestone accounted for 13.6 feet or 82~ of the outcrop thickness. The ' limestone is distributed as block ranging in thickness from 0.5 to 3.1 feet and vertical joints spaced on 1 to 3 foot centers. The ' remaining 2.9 feet of material is distributed as 11 thin bentonite layers having an average thickness of 6 inches. Drilling on other areas within the Dowe Flats valley has indicated an average limestone thickness of 20 feet (Masters 1957). The overlaying Smokey Hill Member of the Niobrara Formation is generally described as a dark gray, cancerous, fossiliferous marine ' shale. However, characterization of the Smoky Hill Member as shale on a regional scale does not account for several separate limestone beds present in the Dowe Flats vicinity. At Dowe Flats, limestones ' within the Smoky Hill Member have been described as an outcrop along the Little Thompson River and mapped in the Dowe Flats area (Masters 1957). An 11-foot thick limestone unit 100 feet above the base of the Smoky Hill Member was mapped by Mailed in Dowe Flats, but was not described by Quam in the Little Thompson River outcrop. ' 97 i