Page:The Journal of geology (IA journalofgeology11893univ).pdf/149

upon comparing the amount of leaching in the two districts. In the earlier drift sheet it is rare to get a response with acid within six to eight feet of the surface, whereas in the newer drift the leaching has seldom been carried to so great a depth as six feet. It seems clear from the position and relations of this old surface that the leaching took place before its burial.

Concerning the amount of valley erosion accomplished in south-western Ohio during this interval no conclusion was reached. Sufficient time was not given to the study of the region to successfully eliminate the effects of post-glacial erosion and of erosion accomplished between the deposition of the silt and the invasion which produced the older moraine of the later drift. In eastern Indiana, however, there are exceptionally favorable conditions for determining the amount of erosion accomplished between the deposition of the earlier and later drift sheets, and it is believed that data of some importance can be furnished. Near the head waters of the Whitewater river there is a district covered by a thick deposit of drift. We may judge from wells made on interfluvial tracts that the level of the rock surface in that region is no higher than the valley bottoms of the several headwater tributaries of West Whitewater, and these valleys are, therefore, simply channels cut in the drift. The evidence all opposes the view that the ridges and valleys are in any way dependent upon preglacial erosion. The valleys along these headwater tributaries of the West Whitewater (Noland's fork, Green's fork, and West fork) are conspicuous for their size, their width being one-fourth to one-half mile or more and their depth sixty to one hundred feet. A similar broad valley is occupied by the headwaters of East Whitewater, though this stream has, since the later ice-invasion, cut a narrow gorge down into the rock strata.

The district of eroded drift was overridden by the western edge of the Miami and the eastern edge of the East White River lobe of the later incursion, but it so happens that the amount of drift deposited does not greatly conceal the outlines of these old valleys, the general thickness of the later drift sheet in this region