Some information on Ohio geology and Botany from “Linking Geology and Botany… a new approach” by Jane L. Forsyth
1. The western part of Ohio is underlain by limestone, a relatively non-resistant rock that does not last long in our humid climate. This stone has been worn down leaving a rather flat landscape throughout western Ohio. Eastern Ohio, is underlain by sandstone, a more resistant stone, interlaced with shale. As the shale eroded away except for where it was capped by sandstone, steep sided hills and valleys were carved out.
2. The original sequence of sedimentary rocks is limestone, overlain by shales, overlain by sandstones, which was then tilted into a low arch as a product of pressure, before erosion began. The limestone throughout western Ohio was eroded away, leaving this part of the state a flat plain. Further east, the sandstone was not removed resulting in the sandstone hills. Most of the erosion of the limestone was done by the Teays River, which was present in Ohio for about 200 million years.
3. The steep-sided sandstone hills in Eastern Ohio greatly slowed the glaciers and led to a glacial boundary.
4. Glacial till is the deposition left behind by the melting of glacial ice, composed of sand, silt, clay and boulders. In western Ohio the glacial till is rich in lime and clay while in eastern Ohio most of the till contains very little lime and clay.
5. In western Ohio, most of the substrate is relatively impermeable, high in lime, poorly drained and inadequately aerated, but with relatively high nutrients. In eastern Ohio, the substrate is very acidic, low nutrient, and permeable.
6. Some plants that have a distribution generally limited to limestone or limey substrates are Cercis canadensis (redbud), Juniperus virginiana (red-cedar), Rhus aromatica (fragrant sumac), Celtis occidentalis (hackberry), and Fraxinus quadrangulata (blue ash).
7. Some species of trees/shrubs that have a distribution generally limited to high-lime, clay-rich substrates developed in the thick glacial till of western Ohio are Acer saccharum (sugar maple), Fagus grandifolia (beech), Quercus borealis (red oak), Fraxinus americana (white ash) and Quercus bicolor (swamp white oak).
8. Some species that have a distribution generally limited to sandstone hills of eastern Ohio are Quercus montana (chestnut oak), Oxydendrum arboreum (sourwood), Pinus virginiana (scrub pine), Pinus rigida (pitch pine) and Tsuga canadensis (hemlock).
9. Sweet buckeye does not occur inside the glacial boundary whereas hemlock is also present in unglaciated eastern Ohio but has a distribution that extends far to the north. Rhododendrons are present south of the glacial boundary although they do not occur everywhere throughout the unglaciated area.