40 GEOLOGY OF OHIO. 



The annals of the geological structure of Ohio are comparatively 

 short and simple. All the movements that have affected its strata have 

 been of the continental type, i. e., slow and gentle and unaccompanied by 

 fractures, displacements, or the formation of well-marked arches and 

 troughs. The dominant forces in all movements which we can trace 

 have been two-fold ; first, that growth of the continental nucleus to the 

 southward which began in the earliest era and which was maintained 

 throughout paleozoic time, and, secondly, the system of northeast and 

 southwest foldings of the eastern border of the continent, which culmin- 

 ated in the formation of the great Appalachian mountain system. The 

 latter division of these forces is the more conspicuous. It was displayed 

 in the first emergence of the rocks of the state above the surface of the 

 sea. The approximate date of this emergence is the close of Lower 

 Silurian time. 



The Cincinnati Axis. 



Under the above designation, the most important fact in the early 

 history of the geological structure of the state is known. The best ac- 

 count that has been given of it is that of Newberry which is found in 

 Geology of Ohio, Volume I, page 90. This account needs to be sup- 

 plemented by the facts given in Volume II, page 411, and in Volume 

 VI, page 46. 



About the close of Lower Silurian time a broad and very flat arch 

 made its appearance in Ohio at its southwestern corner. This arch had 

 already traversed Tennessee and Kentucky in a northeasterly direction, 

 and upon the geology of these states it exerted a profound influence. 

 Newberry counts this elevation due to the same cause by which the great 

 mountain arches of the Atlantic border were long afterwards formed, 

 namely, the crumpling of the crust, due to its contraction by cooling, the 

 force acting at right angles to the Atlantic coast line. The direction of the 

 Cincinnati axis is approximately the same as that of the later axes of 

 elevation, namely, north of east and south of west. In Ohio and Indiana, 

 this important feature proves to be much less simple than was formerly 

 supposed. This has been shown in Geology of Ohio, Volume VI, page 

 41. The main axis is there proved to have, in western Ohio and in 

 Indiana, a northwesterly instead of a northeasterlj' trend; but a subor- 

 dinate elevation branches from it on the western border of Ohio in Mer- 

 cer county and traverses northern Ohio to the shore of Lake Erie. 

 Possibly it crosses the lake basin into Canada. 



There are probably other lines of slight elevation in southern Ohio 

 that go back for their origin to an earh* date. The few facts that we have, 

 bearing on the structure of the Lancaster gas field, for instance, seem to 

 point to such a date of the uplift upon which its gas production depends. 

 But such conclusions can be derived only from the results of the drilling 



