1. Angel JC, Nelson DP, Panno SV (2004) A comparison of manual and a GIS-based method for determining sinkhole density: An example from Illinois’ sinkhole plain. J Cave Karst Stud 66(1):9–17
2. Becker HK (1929) Hohle und Erdbeben. Mitteilungen Uber Hohlen Und Karstforschung 14:130–133
3. Becker A, Davenport CA, Eichenberger U, Gilli E, Jeannin PY, Lacave C (2006) Speleoseismology: a critical perspective. J Seismol 10:371–388
4. Berkson A (2009) Discover Illinois archaeology, 3rd printing. Illinois Association for Advancement of Archaeology and the Illinois Archaeological Survey, Springfield, 27p
5. Brannon JC, Podosek FA, McLimans RK (1992) Alleghenian age of the Upper Mississippi Valley zinc-lead deposits determined by Rb-Sr dating of sphalerite. Nature 356:509–511