Paleontology and geology
There are no Precambrian rocks exposed at the surface in Arkansas. What we know about Arkansas’ Precambrian comes from drill cores and from the interpretation of geophysical evidence, such as deep seismic profiles. The presence of both extrusive igneous rocks (rhyolite) and intrusive igneous rocks (granite) tells us that there were active volcanoes in what is now northern Arkansas during the Precambrian, and that some of the magma that fueled these volcanoes never reached Earth’s surface. The magma that erupted formed the rhyolite, and the magma that cooled below the surface formed the granite.