324 Foerste — Or dovician- Silurian Contact in the 



This argument also lias lost force since it has been discovered 

 that along the western flank of the geanticline the conspicuous 

 thinning of Niagaran formations toward the east is confined to 

 the edges* of the Niagaran formations, where in succession 

 they project from beneath the immediately overlying Niagaran 

 beds on approaching the crest of the geanticline ; and where 

 the thinning of the strata might have been caused by erosion 

 subsequent to their deposition. The same strata fail to show 

 any conspicuous thinning eastward where the immediately 

 following subdivision of the Niagaran is present. Under these 

 conditions it is not possible, without further evidence, to exclude 

 the alternative proposition, that the Niagaran, at least the 

 Clinton and the equivalents of the Osgood clay, originally may 

 have extended across the region of the present Cincinnati gean- 

 ticline, gradually thinning out westward; that during late Silu- 

 rian or early Devonian times a geanticlinal uplift occurred, accom- 

 panied by removal of Silurian strata along the crest of this uplift 

 and resulting in a conspicuous thinning of the edges of the vari- 

 ous Niagaran strata toward the crest of the geanticline where- 

 ever exposed by the removal of overlying Niagaran formations. 

 This alternative proposition would demand the operation of 

 geological processes resulting in baselevelling, the Devonian for- 

 mations being deposited upon the baselevelled edges of the 

 Niagaran. It should be remembered however that, at present, 

 evidence favoring baselevelling of Niagaran strata is confined 

 to the conspicuous thinning of the edges of Niagaran formations 

 toward the crest of the geanticline where not protected by the 

 next overlying Niagaran formations, and the absence of a 

 similar conspicuous thinning in the same direction where the 

 next overlying Niagaran formation is present. It seems 

 scarcely possible that baselevelling could have taken place over 

 areas as large as those exposed along the crest of the Cincinnati 

 geanticline without leaving other evidence than that offered 

 by the thinning of strata as just described. 



During the earlier operations of the Geological Survey of 

 Ohio under Professor Or ton, thin layers of conglomerate were 

 discovered in the Clinton at Belfastf in Highland county, 57 

 miles east of Cincinnati, Ohio. The fossils in the pebbles of 

 this conglomerate were believed to have been of Ordovician 

 age, but subsequent investigations proved their Clinton origin, 

 and that older strata of Clinton age had been broken up during 

 the formation of this conglomerate. The presence of conglom- 

 erate was believed to be conclusive evidence of the pre-Niag- 

 aran origin of the Cincinnati geanticline. It is scarcely neces- 



* Silurian and Devonian limestones of Tennessee and Kentucky, Bull. Geol. 

 Soc. Am., 1901, pp. 408-414, fig. 5. 



fOhio Geol. Kept., Surv. for 1870, p. 270. On Clinton conglomerates and 

 wave marks in Ohio and Kentucky, Journ. Geology, iii, 1895, pp. 1-4, 22-26. 



