GLACIAL SUCCESSION IN OHIO. I 37 



some length, in a recent paper.' It need, therefore, be but briefly 

 touched upon here. It is there shown that it forms a practically- 

 continuous sheet over the southern portion of the glaciated dis- 

 trict in Ohio and Indiana, and extends to an undetermined dis- 

 tance over the unglaciated districts of Ohio. It also appears on the 

 uplands in Kentucky, south-west of Cincinnati, and may appear 

 further east in that state. It has been found along the margin 

 of the glaciated district in Ohio as far north-east as the vicinity 

 of Newark, but has not been observed farther north and east. 



The thickness of this silt decreases in passing southward, espe- 

 cially on the interfluvial tracts of south-western Ohio and south- 

 eastern Indiana, a fact which seems to indicate that its source 

 was from the north rather than from flooded conditions of the 

 Ohio river. From evidence gathered in the upper Mississippi 

 region, it is thought to be the correlative of a sheet of glacial drift 

 not exposed to view in these states, or at least not yet discovered. 

 Its thickness in the northern part of the district, next to the 

 outer moraine of the newer drift, is four to six feet or more while 

 on the borders of the Ohio river it scarcely exceeds three feet, 

 and in places is two feet or less. Wherever examined it is found 

 to be thoroughly leached. This fact is thought to be of impor- 

 tance in showing great age, especially on the theory of the 

 glacial origin of the silt, since glacial silts, as well as till, in 

 regions underlain as this region is by limestone, contain a large 

 amount of calcareous material. 



The amount of depression involved in this subsidence is 

 difficult to determine. As yet such data as have been dis- 

 covered bearing upon the altitude of the land, either previous 

 to or during the depression, are not precise, though it seems 

 probable that the altitude was several hundred feet lower at the 

 maximum of depression than at the present time, while before 

 the depression the drainage appears to have been good, and we 

 may suppose that the altitude was not much lower than at the 

 present time. 



'"On the Significance of the White Clays of the Ohio Region." American 

 Geologist, July, 1892. 



