Art III.] Carney, Geology of Perry Township. 1 29 



versal ; and an equally obvious cause for the reversal is sug- 

 gested in the glacial dam.^ Although the drift deposits com- 

 pletely fill the valley at the point of its debouchure into the 

 broader east-west valley, thus affording the requisite conditions 

 for a ponded water body that would rise to a spill-way some- 

 where about its rim, yet a field study of the basin that must 

 have been involved in such a static body suggests the advisa- 

 bility of considering other causes that might produce the same 

 reversed drainage. 



The tributary valleys of this hypothecated lake-basin were 

 favorable to the formation of deltas ; but no deltas exist any- 

 where about the basin. The irregularly dissected shores fur- 

 nish numerous profiles to register wave work in the formation 

 of cliffs and bars ; but we find neither. The absence of clays 

 suggests that a lake could have existed here but a short time, 

 if at all. Furthermore the valley-train frontal appearance of 

 the drift area, which constitutes the glacial dam, is evidence 

 pointing to the same conclusion as does this absence of shore 

 phenomena. 



Whatever cause has effected the reversal, the stratigraphy 

 of the area has been an important control in the working out of 

 that cause. The original horizontal beds in this part of the 

 State are undisturbed save for broad low folds decreasingly 

 characteristic as we come westward from the axis of the Appal- 

 achian movement. In vertical section, however, (Plate 2,) the 

 formations in eastern Licking county at least are sharply differ- 

 ent in texture, hence in capacity to resist denudation. 



The Sharon conglomerate apparently marks the limit of 

 down-cutting reached in the Cretaceous base-level cycle. This 

 formation is underlain by the thin bedded sands and sandy 

 shales of the Logan. Stream erosion was held up by the coarse 

 silica-cemented Sharon, but after this conglomerate horizon had 

 been incised, erosion proceeded more easily in the Logan ; and 

 through planation the Sharon cliffs were undercut thus widen- 



'Clark, W. B. Bull. Sci. Lab. Denison Univ. vol. xii, p. 8. 



