666 THE JOURNAL OF GEOLOGY. 
siderable, for there can be no question but that in this region 
glacial deposition greatly exceeded glacial erosion. The quartzite 
range is not simply an inter-stream ridge; it is an elongate 
monadnock standing up out of a very extensive peneplain. The 
amount of erosion necessary to isolate it was much greater, and 
demanded a very much longer period of time than would have 
been necessary simply to cut valleys 700 or 800 feet deep. 
Looked at from this standpoint, one is inclined to think that the 
age of the gravel may be as great as Cretaceous. On the other 
hand the total amount of erosion which has taken place in the 
upper Mississippi basin since the deposition of the gravel is but 
a fraction of that which is believed to have taken place in some 
parts of the west in late Tertiary and post-Tertiary time. 
Although the topographic relations ot the gravel do not enable 
us to fix its age in the accepted terms of geological chronology, 
they seem to bring out the general fact that the present physical 
features of the upper Mississippi basin are of later origin than 
has been generally supposed. This is especially true if the 
gravel shall prove to be Tertiary, and the balance of evidence 
seems at present to favor this interpretation. 
There is still another direction in which the gravel bed at 
Devil’s Lake is of interest. The fossil content of the gravel, as 
well as the greater quantity of chert, indicates that it was derived 
in considerable part from the Niagara limestone. It has long 
been believed that the Niagara limestone of Wisconsin, now 
confined principally to the eastern margin of the state, once 
extended much farther west, over regions whence it has been 
removed. The constitution of the gravel affords an interesting 
confirmation of this belief, and seems to indicate that the Niagara 
may have had even a greater extent than has been supposed, for 
it can hardly be doubted that, when the gravel was formed, the 
limestone either overlay the quartzite, or existed at some equally 
high point in the immediate vicinity. Not only this, but the 
presence of one fossil, orthoceras junceum, which, so far as known, 
can be referred only to the Trenton or Galena, suggests that one 
or both of these formations also once passed over the quartzite 
