PREGLACIAL GRAVELS NEAR BARABOO, WIS. 665 
looked upon as impossible, therefore, that both Cretaceous and 
Tertiary gravels may have extended as far north as Wisconsin. 
If so, it is possible that remnants of both still exist, though 
until we have positive evidence of two formations, the presump- 
tion is in favor of but one. 
Whatever the age of the Devil’s Lake gravel, its topographic 
position is full of significance. It occurs on one of the highest 
points of the state. Within the driftless area, where such gravel 
as this might have escaped destruction if it ever existed, there is, 
we believe, but one other point so high as that on which the 
gravel occurs. This is the Blue Mounds. Onthe crests of these 
mounds, corresponding gravel is not known to occur, though 
they have never been examined, so far as known, with this point 
in view. 
It is clear that the gravel could not have been deposited in 
its present position, since the existing topography was developed. 
The ridge on which it occurs is about 700 feet higher than the 
Barbaoo River to the north, and about 800 feet higher than the 
Wisconsin River to the south, and, what is still more significant, 
it is 500 or 600 feet above the general level of the extensive 
drift-covered sandstone plain which surrounded it. Since the 
gravel is not glacial, there is but one interpretation possible con- 
cerning the topographic conditions and relations at the time it 
was deposited. At that time the surface on which it occurs was 
not higher than its surroundings. This fixes the age of the 
gravel in terms of erosion. It was deposited before the quartzite 
ridge was isolated, that is while the Potsdam and later forma- 
tions still reached the top of the harder quartzite. 
The amount of erosion which has been accomplished since 
the gravel was deposited is, therefore, very great. It should be 
noted that this erosion is not measured simply by the excavation 
of valleys on either hand to the depth of 700 and 800 feet 
respectively. Since the gravel was deposited, the general surface 
of the surrounding country has been cut down to the extent of 
500 to 700 feet, disregarding the heavy drift deposits which have 
helped to build it up again. This building up process was con- 
