Quarry Layers

Quarry Layers. . , This former quarry reveals the area's basic geologic layers. Beneath a cover of soil, the thick, pink-tinted layer of Sioux quartzite covers the tin, red-colored lower layer of pipestone - the prized stone of many tribal groups. As the slant of the quarry floor indicates, the rock layers angle deep into the earth. , Geologic pressures created the pipestone and quartzite layers over the past one billion years. Formed at the bottom of an ancient ocean, these layers of sediment were gradually compressed into stone and uplifted over the ages. The thick layers above and below the pipestone contained mostly silt and became quartzite. But the thin layer between was composed of fine clay - the reason the pipestone can be so easily worked. , The quartzite and pipestone layers visible here - and another thick layer of quartzite below them - dip toward the east at a 5-10 degree angle. As pipestone quarrying continues, an ever increasing quantity of the upper quartzite must be removed.