Laserfiche WebLink
generally fine-grained, of lov porosity and are well-cemented. Some <br />shalea, moat claystones and all coal seams were formed in back- <br />barrier and near marine enviro~ents. The very thick shale <br />formations, such as the 700-foot shale member below the Tventymile <br />Sandstone, are offshore marine formations and are characterized by <br />their lateral continuity, eatremely fine-grained nature and <br />eatremely low horizontal and vertical permeability. <br />The youngest rocks exposed in the proposed permit and adjacent <br />areas belong to the massive, marine-deposited Lewis Shale. Near the <br />base of the Levis Shale is the Fish Creek Seam, approximately two <br />feet thick. Approximately 60 feet of shale and siltstone separate <br />the Fiah Creek Seam from the massive Twentymile Sandstone below. <br />• The Twentymile Sandstone is a key mapping unit and can be identified <br />and traced throughout most of the Yampa Coal Field. Its properties <br />as as aquifer are fair and it will yield sufficient water only for <br />limited stock or household use where saturated. The rock below the <br />Twentymile Sandstone is another massive marine shale member and <br />averages about 700 feet in thickness. <br />The Fish Creek Seam, the Twentymile Sandstone, and the thick <br />marine shale make up the majority of the Williams Fork Formation. <br />The lower portion of the Williams Fork consists of coal-bearing <br />shalea, claystones, ailtatones, and some thin sandstone layers. The <br />top of this coal-bearing member is characterized in places by a <br />• discontinuous fine-grained sandstone bed which ranges in thickness <br /> from 0 to 10 feet. Just below this sandstone bed is the equally <br /> 2.04-26 <br />