Looking at the Badlands in South Dakota it is hard to imagine that it, like much of the middle of the United States, was once covered in a shallow ocean. As plants and creatures died they sank to the sea floor. Over time these layers were compressed and formed Strata, which is layers of sedimentary rocks. One of these layers of sedimentary rocks found in the Badlands is Pierre Shale. This layer is distinctly darker than much of the other layers found here.

As time passed and the ocean gave way to land, trees and other forms of vegetation grew and died. As they died they decomposed forming areas of peat. After time the peat was covered by sediments and eventually through pressure was transformed into Lignite Coal. Lignite Coal is referred to as the brown coal and is considered the lowest rank of coal. This is largely because of its high moisture content and low energy density. It is mined and used for energy in the United States but more prevalently in European countries.

There isn't a lot of volcanic activity or evidence in the Badlands area. But there are layers of Bentonite, which is largely made up of compressed volcanic ash. The majority of this volcanic ash likely came from the Yellowstone area and was carried east into South Dakota. Over time rain washed the ash into lakes and rivers where it was concentrated and eventually covered with sediment and compressed over time.

Although there is not a lot of volcanic activity in the Badlands there are similar formations to those of volcanic landforms. One example of this is the clastic dike in the Tertiary strata of the Badlands. A dike formed from by volcanic activity is lava flowing vertically in fractures. A clastic dike is formed similarly but instead of lava sediment fills the vertical fractures.

Sources: http://maps.unomaha.edu/Maher/PRF09site/clasticdikes/clasticdikeintro.html http://www.nps.gov/badl/naturescience/Geologic-Formations.htm# http://en.wikipedia.org/wiki/Lignite http://en.wikipedia.org/wiki/Bentonite