338 Foerste — Ordovician- Silurian Contact in the 



Quaquaversal dips may have existed even before the deposi- 

 tion of the Niagaran.. The variations in thickness of the 

 Clinton in some parts of Kentucky and Tennessee are of an 

 irregular character and can not be correlated in such a manner 

 as to demonstrate the presence of the Cincinnati geanticline in 

 pre-Niagaran times. The presence of wave-marks and pebbles 

 in the Clinton of Ohio, Indiana, and northern Kentucky may 

 have been connected with the existence in early Silurian times 

 of very low irregular elevations of land of comparatively small 

 extent in a very shallow expanse of sea covering wider areas. 

 Similar wave-marks and pebbles are found at various elevations 

 in the Richmond group in southwestern Ohio,* northern Ken- 

 tucky, and southeastern Indiana. 



The formation of the Cincinnati geanticline probably began 

 with a general elevation of the sea bottom over wide areas, 

 producing shallow waters. The irregular distribution at dif- 

 ferent levels of wave-marks and pebbles in rocks of Richmond 

 age show that during late Ordovician times the waters were 

 locally sufficiently shallow to bring the sea bottom within the 

 range of action of waves, some parts being probably exposed 

 to the air, at least at low tide. Along the western ranges of 

 the Alleghanies there may have been a wide expanse of dry 

 land, since the Richmond is absent eastward. Later there was 

 a depression of the area eastward permitting the deposition 

 there of the neo-Niagaran, but no deposits of this kind are 

 known in the region of the Cincinnati geanticline, although 

 their existence has been inferred in eastern and northern Ohio, 

 below the cover of later rocks, from the records of drillers. 



During early Niagaran times the depression appears to have 

 progressed sufficiently to permit of the deposit over wide areas 

 of the Clinton. There is no evidence, however, that the 

 Clinton ever reached the western half of Indiana and the 

 adjacent part of Kentucky. During the Clinton irregular 

 shallow water conditions prevailed in certain areas. The 

 Osgood clays may formerly have extended across the region of 

 the present Cincinnati geanticline. The moderate quaqua- 

 versal dips of the earlier part of the Niagaran were followed 

 in some areas by the stronger quaquaversal dips of the later 

 Silurian. Just when the changes in level involved resulted in 

 the production of the initial stages of the axis of the present 

 Cincinnati geanticline is unknown, but it probably preceded 

 Devonian times since in the Meso-Devonian the Cincinnati 

 geanticline had attained considerable development. 



While the origin of the Cincinnati geanticline in pre-Meso- 

 Devonic times can be demonstrated, it owes its present propor- 

 tions chiefly to later orogenic processes. In Ohio, the labors 

 of Professor Orton have demonstrated to what a remarkable 

 extent the present development of the geanticline was depend- 



* Journ. Geol., 1895, pp. 6, 7, 9-11. 



