Lost River - Karst Information Portal

2007 NSS Convention Guidebook
Along U.S. 150 there are numerous
exposures of the Borden, the Ramp Creek
Formation, the Harrodsburg Limestone, the
Salem Limestone, the St. Louis Limestone
grading into the Ste. Genevieve from east to
west. The massive and lighter colored Salem
Limestone has distinctive and easily recognized
cross-bedding, while the darker colored and
fossiliferous Ramp Creek and Harrodsburg
limestones contain the vast majority of the
famous southern Indiana quartz geodes and
many large crinoid stems. The argillaceous
140
Figure 37. Location of Geology trip stops 6 through 10 on the regional geologic base map
(modified from Camp and Richardson, 1999).
and thinner bedded nature of the St. Louis is
distinct from the Salem and the overlying Ste.
Genevieve.
The Mitchell Plain and associated
physiographic units are generally thought to
have been largely developed in the Miocene
Epoch of the Tertiary Period, or about the
last 25 million years. During the Quaternary
Epoch (the last two million years) the features
have continued to evolve, with the numerous
glacial periods adding new influences such as
periglacial conditions (ice margin freezing)