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<br />with it, and the Trout Creek Sandstone at the top of the formation. The shale <br />between these sandstones is of marine origin, is light to medium grey in color and <br />tends to include progressively greater amounts of silt and fine sand in an upward <br />direction. Sandstones within the Iles are thought to represent beach, delta front and <br />shallow marine environments. The coarsening upward shale is thought to indicate a <br />trend toward transgression of the sea across the land. <br />Williams Fork Formation <br />The Williams Fork Formation (K,,,, on Exhibits 2.1-I and 2.1-2) is of greatest <br />interest for it contains the coals that are being recovered by the Edna Mine. It rests <br />conform ably on the Trout Creek Sandstone and consists of from 1,300 to more than <br />1,500 feet of marine sandstone, shale and coal. Previously proposed stratigraphic <br />terminology has been adopted and modified to maximize its usefulness for the study <br />area. The Williams Fork is thus divided into Three members: a lower coal-bearing <br />unit, a marine shale member, and a sequence of sandstones and shales at the top. <br />The lower coal-bearing member is composed chiefly of siltstone and shale with <br />Thinly bedded sandstones and coal. These bituminous coals include, in ascending <br />i order, the Wolfcreek, Wadge, and Lennox coals. This sequence is interpreted os <br />deltaic sediments. Sandstones are thought to represent channel and/or tidal flat <br />deposits; shales correspond to interlobate areas and coals represent marsh and swamp <br />environments. <br />The marine shale member consists of 550 to 600 feet of medium to dark grey <br />shale and siltstone containing a few thin beds of fine grain sandstone. Because these <br />fine grain sediments indicate a lower energy environment, and hence deeper water, <br />this member is thought to represent marine transgression. <br />The upper member consists of a sequence of interbedded sandstones and shales <br />that can be interpreted as cyclical sedimentation. Each cycle begins with a <br />transgression of the sea and the deposition of shale in o relatively low energy <br />environment. Each cycle is concluded by the deposition of sand, often displaying <br />bioturbation and burrows such as Ophiomorpha, as well as root casts typical of the <br />shallow, high energy environments located close To sea level. The culmination of <br />each major depositional cycle is marked by regression of the sea and is designated <br />by a "K" which stands for "key." Based on surface and subsurface information, six <br />(KI through K6) Key horizons were defined. KI and KZ occur below The Twentymile <br />2.1-2 <br />