PREGLACIAL GRAVELS NEAR BARABOO, WITS. 659 
much of the gravel which occupies the lower lands and the val- 
leys of the same general area, represents a younger formation 
derived from the older. It is also believed that the valleys and 
lowlands in which the latter class of gravels are found, were 
developed by subaérial erosion from the plains on which the 
high-level gravels occur, after the latter were laid down. 
The northward extension of these high-level gravels of the 
south has never been determined. It has long been known that 
they reached as far north as Pike and MHancock counties, 
Illinois.” 
In August, 1891, a paper was read before the Geological 
Society of America,” in which attention was called to the exis- 
tence of certain isolated and hitherto unknown beds of high-level 
gravel, lying farther north than most of those previously known, 
and believed to be their equivalent At that time the gravel 
had been found at various points as far north as Adams county, 
Illinois, where it was found to underlie the glacial drift. Where 
the new finds of gravel were made, in Calhoun, Pike and Adams 
counties, the beds occur, as in the earlier known localities, on the 
crests of high hills or ridges, or on high plateaus, positions which 
clearly indicate that the formation was deposited long before the 
surface had assumed its present topography. Since the gravel 
underlies the glacial drift of this region at but a few points, and 
thesé the most elevated, and since its materials do not enter into 
the constitution of the glacial drift in any large quantity, there 
is no room to doubt the conclusion that the high-level gravel of 
western and southwestern Illinois had been largely removed by 
erosion before the glacial drift was deposited. Since the amount 
of erosion involved is large, affecting not only the gravel but 
also the underlying indurated strata, and since the overlying 
drift belongs to the earlier part of the glacial period, there is 
little room to doubt that the gravel is preglacial, and, therefore, 
according to the commonly accepted standard of classification, 
pre-Pleistocene. 
™Geol. Surv. of Ill., Vol. I., p. 331, 1866; Vol. IV., p. 37, 1870. 
2SALISBURY; Bulletin of the Geol. Soc. of Am., Vol. III., p. 183, 1892. 
