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<br />Section 719.14(a) Continued. Rule 2.04.6 <br />conglomerates, at the base of which is a massive 50 foot thick sandstone. <br />The lower 3,500 feet of the Coalmont Formation is the coal-bearing portion <br />of the formation, most of which is characterized by dark gray shale with <br />occasional thin banks of sandstone. <br />The main coal seam of the Coalmont Formation, the Sudduth Seam, lies 50 <br />feet above the Pierre Shale contact and is separated from this contact by <br />fine-to-medium-grained sandstone. The Sudduth coal seam, which is the <br />objective of the proposed mining operations within the mine plan area, has <br />a stratigraphic thickness which varies between 36 and 75 feet and which <br />averages approximately 50 feet. The Sudduth Seam is the only aquifer to <br />be disturbed by the proposed mining activities. A detailed discussion on <br />the hydrologic characteristics of this aquifer is presented in Section <br />779.15. Directly above the coal seam is a zone of shale with occasional <br />lenticular sandy zones ranging in thickness from 90 to 139 feet and <br />averaging 121 feet. Above this shale zone is a zone of shale interbedded <br />with numerous small, lenticular beds of sandstone. This zone averages <br />more than 300 feet in thickness. Near the top of this zone and about 400 <br />feet above the Sudduth Seam are occasional very thin (less than 6 inches), <br />discontinuous beds of coal. About 1,500 feet above the Sudduth Seam is <br />a 500-foot thick layer of very dark brown to black carbonaceous shale. <br />Lying unconformably above the Coalmont Formation and still within the mine <br />plan area is the North Park Group, most commonly known by its three (3) <br />individual formations; The White River (oldest), the Brown's Park, and <br />the North Park (youngest). These format tons total about 600 feet in <br />thickness and are composed of shales, volcanic ash, tuff, and <br />conglomerates. A massive sandstone forms the base of the North Park <br />Group. <br />The youngest strata exposed near the mine plan area are deposits of sand, <br />• gravel, clay, dune sand, and glacial till of Quaternary age. All of the <br />Quaternary deposits lie unconformably on the older rocks of the North Park <br />Formation. <br />779-12 b Revised-Apri1.1990 <br />