GEOLOGY. The principal feature in the geology of Ohio is the broad fold or anticlinal whose axis: extends from central Kentucky and crosses southwestern Ohio near Cincinnati, thence run ning, northwest into Indiana, while a branch axis runs northeast toward the western end of Lake Erie. From this axis the strata dip gently in either direction, so that a broad area of Silurian rocks is exposed. covering, southwestern Ohio, southeastern Indiana, and north central Ken tucky, with a narrower band along the branch axis toward Lake Erie. A small portion of this area near Cincinnati is composed of Lower Silurian rocks known as the Cincinnati group. On either side of the Silurian are narrower outcrops of Devonian strata running on the one hand through central Indiana, and 00 the other through the whole length of Ohio a little West of the central line. he lateral outcrops of these strata along the branch axis occupy the north western corner of the State and a narrow belt along the entire southern shore of Lake Erie.
The remainder of Ohio, including nearly the whole eastern half, consists of Carboniferous strata. The entire State scents to have been above sea level throughout the Mesozoic and Cenozoic eras, there being no formations later than the Carboniferous until we come to the glacial drift. This covers about two-thirds of the State, leaving the southeastern portion un touched by the ice invasion. The drift deposit is in some places several hundred feet thick, and consists of alternating layers of boulder clay, stratified sand, finely laminated clay, sandy clay, and gravel. Raised beaches showing the former extent of the Great Lakes have been traced through the State, and another interest ing feature of the surface are the deeply carved river-valleys which are completely filled with Janis, so that the rivers sometimes flow far above their former beds.