Rocks and minerals of the Glaciated Region

Loess. A widespread, fine-grained blanket deposit, loess consists predominantly of silt. Silt, as geologists define it, is a rock fragment or mineral particle smaller than a very fine sand grain and larger than clay: its diameter is between 1/16 mm and 1/256 mm. Windblown silt deposited during the Pleistocene is known as loess.

As glaciers advanced, they pulverized rocks and sediments in their path. As they melted, this pulverized rock, or silt, was deposited on the floodplains by streams coming from the melting ice sheet. Temperature differences between the snow-covered regions to the north and the bare ground to the south may have created large differences in atmospheric pressure, resulting in strong winds capable of moving large amounts of silt.

Thick deposits of loess, more than a hundred feet thick in places, occur along the bluffs of the Missouri River. The loess in this region is typically a yellowish-buff, porous silt that crops out with steep faces along hillsides and valley walls. Small, white shells of snails also may be found in the loess. In northeastern Kansas a very rich soil has developed on the loess, especially in Brown and Doniphan counties and along the bluffs of the Missouri River as far south as Kansas City. Loess hills in Doniphan County are some of the highest in the state. One of these, Lookout Mountain north of Sparks, is more than 350 feet above the floodplain of the Missouri River.

Glacial erratics. The boulders and pebbles from local and distant rocks that were carried by glaciers are of many different types, including limestone, sandstone, quartzite, granite, and basalt. Rocks that have been transported into an area from far away are called erratics. Among the glacial erratics in northeastern Kansas, quartzite is one of the most common. Quartzite, a metamorphic rock, is quartz sandstone that is so thoroughly cemented with silica (SiO₂) that the rock breaks through the grains as easily as around them. It is harder than sandstone and cannot be scratched by a knife. The quartzite boulders in the Glaciated Region are known as Sioux quartzite because they come from the area where Sioux quartzite crops out in the area around Sioux Falls, South Dakota.