Ohio is actually divided into to geographically and geologically different parts. The west is the central lowland with its till plains and the great lakes plains. The eastern part is formed by the Appalachian Plateaus or Allegheny Plateaus. While in general the lowland are less likely karstified than the highlands, in Ohio the show caves are distributed actually in opposition to this rule of thumbs. One is located right in the middle of the plains, and two are actually on an island in Lake Erie. The rugged hills and forests of the unglaciated Allegheny Plateau in the southeast of the state are composed of sandstone, and there is a number of rather small erosional sandstone caves and natural bridges.