PREGLACTAL GRAVELS NEAK BARABOO, WIS. 661 
derived from the pre-Pleistocene chert gravel were thought to 
enter as constituents into the drift, are 100 to 125 miles north of 
the northernmost point in Adams county, where the formation is 
known to occur zm setu. At many intermediate points, similar 
materials were found in the glacial drift. Quantitatively they 
are unimportant, and their absence is more common than their 
presence. Their occurrence and distribution in the drift are such 
as would have resulted had erosion remnants of the high-level 
gravel existed when the ice invaded western Illinois. 
In the paper referred to it was stated that certain limited 
beds and scattered remnants of hitherto unexplained quartzose 
gravel were known to exist within the driftless area of Wiscon- 
sin, and the suggestion was hazarded that these gravel remnants 
were very likely to be correlated with the gravels further south. 
The remnants of gravel in Wisconsin occur at various points 
from Crawford county on the south, to Dunn county on the 
north. Wherever known, these remnants occur on the crests of 
ridges and the summits of isolated hills. Not only this, but 
they are found on the summits of the highest elevations of the 
‘region within which they occur. They often consist of nothing 
more than scattering pebbles, though beds a few feet in thickness 
are known, the most considerable being near the village of Seneca 
in Crawford county. The gravel is here composed almost wholly 
of quartz.* As at various points further south, the gravel is 
here cemented by iron oxide into a firm conglomerate. The 
average depth does not appear to be more than five or six feet, 
but it has been penetrated to very much greater depths at one or 
two points. The exceptional depths are thought to represent 
the fillings of fissures, which affect the underlying rock. 
Had gravel remnants similar to those of the driftless area 
existed in western Illinois at the time this region was glaciated, 
they would have contributed to the drift of their respective 
localities, just such material as it has been observed to contain. 
They would have made considerable contributions where they 
were considerable, and meager contributions where they were 
*STRONG, Geology of Wisconsin, Vol. IV., p. 88. 
