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26 <br />The Ft. Benton Formation is a 500 foot thick layer of fine <br />grained marine deposits. The lowest part is composed of dark <br />gray to black fossiliferous sandy shales. The middle portion is <br />a zone of light to dark gray argillaceous limestone and dark gray <br />it to black calcareous shales. The u er <br />pp part is calcerous dark <br />gray sandy shales. Numerous thin but laterally continuous <br />bentonite layers are found throughout the formation. The lower, <br />middle and upper parts are often referred to as the Graneros <br />Shale, the Greenhorn Limestone, and the Carlile Shale, <br />respectively. <br />The Codell Sandstone is the uppermost unit in the Ft. Benton <br />' Formation. In the Dowe Flats area, it has a 15-foot total <br />thickness and can be divided into a 7-foot gray siltstone beneath <br />an 8-foot thick silty sandstone. This silty sandstone directly <br />underlies the Niobrara Formation. <br />The Niobrara Formation is traditionally separated into two units, <br />'i the Fort Hays and Smoky Hill members. The Fort Hays Member is an <br />extremely fine-grained, light gray limestone with thin <br />interbedded shales. A section of Fort Hays Member at the south <br />end of Dowe Flats measured 16.5 feet thick (Lowman 1977). <br />Limestone accounted for 13.6 feet or 82~ of the outcrop <br />thickness. The limestone is distributed as block ranging in <br />thickness from 0.5 to 3.1 feet and vertical joints spaced on 1 to <br />3 foot centers. The remaining 2.9 feet of material is <br />distributed as 11 thin bentonite layers having an average <br />thickness of 6 inches. Drilling on other areas within the Dowe <br />Flats valley has indicated an average limestone thickness of 20 <br />feet (Masters 1957). <br />The overlaying Smokey Hill Member of the Niobrara Formation is <br />generally described as a dark gray, cancerous, fossiliferous <br />marine shale. However, characterization of the Smoky Hill Member <br />as shale on a regional scale does not account for several <br />separate limestone beds present in the Dowe Flats vicinity. At <br />Dowe Flats, limestones within the Smoky Hill Member have been <br />described as an outcrop along the Little Thompson River and <br />