Laserfiche WebLink
Strata of [he Williams Fork Formation are comprised of interbedded <br />shale, sandy shale, coal beds and ledge forming sandstones and are <br />approximately 1,800 f[ in thickness. These were lain dawn in alter- <br />. nating marine, brackish, and fresh water environments. The Lewis Shale <br />conformably overlies [he Williams Fork Formation and consists of <br />approximately 1500 to 1900 fee[ of dark gray marine shales. From west <br />to east [he lower boundary of the Lewis Shale deepens eventually to <br />include the upper beds of [he Williams Fork Formation. This is because <br />[he Williams Fork Formation loses some of its sandstone members to [he <br />east. A simplified cross section through the Williams Fork Mountains is <br />shown in Figure 4-1. <br />On the northern portions of [he mine [he Lewis Shale is the surface geo- <br />logic formation. Strata exposed on the higher portions of the Williams <br />•, Fork mountains are those of the Williams Fork Formation. <br />This formation has been divided into 3 units-an upper and lower unit <br />separated by the Twenty Mile Sandstone. On the northern portions of <br />the mine the Lewis Shale is the surface geologic formation. Figure 4-2 <br />~ shows a simplified geologic map of [he mine plan and surrounding area. <br />!t';.:, <br />- The Twenty Mile Sandstone unit is comprised of a [hick main sandstone <br />bed, interbedded sandy shale, shale, coal, another massive sandstone <br />bed, a series of gray and sandy shales and an oyster coquing bed. <br /> <br />•1 <br />-19- <br />