The classic arcuate end moraines of north-central Ohio are veneered with from one to three Woodfordian (Late Wisconsinan) tills and probably predate the last glacial episode. These overridden moraines do not record the history of the latest ice sheet to invade the region.
Overriding and subsequent deglaciation may result in modification of pre-existing moraines in several ways, such as (1) partial removal by scouring, (2) covering the moraine with a layer of drift, (3) filling in intermorainal tracts with drift, (4) deposition of new moraines beside or on top of older moraines, and (5) derangement of drainage with resulting dissection of moraines by meltwater streams.
The total effect is to produce a composite landscape consisting of elements of two or more separate glaciations. The elements of different ages may be distinguished by stratigraphic relations, trend directions, and sharpness of topography, because newer features have changed least. Overridden moraines have a subdued or drowned appearance; at many places only a chain of knolls remains to indicate their presence.
The end moraines in north-central Ohio are multiple, and several additional end morainic elements are present in areas formerly mapped as ground moraine. In the Scioto basin 27 morainic elements can be distinguished and these can be traced northeastward around the Mansfield Highland into the Killbuck basin.
The similarity of form, pattern, and topographic expression of these moraines suggests they are recessional moraines of a single deglaciation. The presence of Millbrook Till, or its lateral equivalent, at the base of many exposures located on the moraines from north central Ohio eastward into Pennsylvania, suggests the moraines are pre-Woodfordian, probably Altonian, and therefore they do not mark Woodfordian till boundaries.