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Northern Coal Company 5. Information should be provided thaC discusses the geology of the area as it pertains to subsidence. For example, since rapidly down-cutting streams, characterized by narrow V-shaped valleys, produce unloading fractures beneath and parallel to the stream valley, there may be an increased potential for subsidence. As a result of subsidence, in addition to the fractures, there may be groundwater communication between strata. Lithologies of the lower third of the Williams Fork Formation are exposed along the sides of the Curtis Creek, an incised drainage. Rocks in the formation consist of interstratified beds of moderately thick massive sandstones, shales, mudstones, laminated sandstones and silts tones, carbonaceous shales and numerous coal beds, 1 to 35 feet thick. Dip of the strata is northerly at about 180 'with a general strike of North 830 East. The extent of surface weathering and its depth of 15 to 27 feet Rave been obtained from shallow drilling along Curtis Creek to the power substation located in Sec. 20, T2N, R93W. This distance includes the area where mining is planned to pass under Curtis Creek. 'Crossing under @urti~s Creek+ nv_i 11 tabe place 'apt •d'epth's of -134 to 1400 feet. These dri 11 i ng resul is show that surface weathering and its effects do not extend to depth or are of sufficient areal extent to encounter the "G" seam or its encompassing strata at the point of crossing. The massive sand sequences consist of predominantly medium grain, well sorted, rounded quartz sand grains, matrix commonly consists of clay particles. Calcic cement is uncommon, often this sand will occur in cuttings as individual sand grains. When encountered in the drill holes, this material occurred at least, 60 ft. above the coal seam. The more competent units consist of the 'silty sandstone facies. These sand units are typically very fine grained to medium grained, poorly sorted, sub- rounded sand with silty matrix material. Minor amounts of calcic cement occur sporatically in this material. Interbedded with these sands are shaly mudstone beds, often silty and rarely fissle. All of the sediments are contential deposits related to a fluvial depositional environment. _. The relatively young age of tha sediments coupled. with the modera~te~degree ~ROf diagenesis allow the rocks to behave in a plastic manner, oweG~ ti-mer,.. rather than as brittle unit"s. This would tend to l.i.,tiit the lateral and depth extension of any fractures which inay be caused by the unloading related to the down cutting of Curtis Creek. r.• A joint and fracture system is observed in the surface and subsurface. This system is regional in extent. It is related to the deformation re- sulting in the sulfur creek syncline. While the fracture system is present, the individual fractures are discontinuous with depth and exhibit no evidence of serving as water channels nor is communication between beds containing ground water evident. In both the Rienau No. 2 Mine and the Northern No. 1 Mine, these fractures account for only minor moisture weeps.