268 Wisconsin Academy of Sciences, Arts and Letters. 
concealed by the rocky point. Plate XIV, Fig. 3, shows this 
last buttress, and the same rocky peak seen from the east. In 
this figure the buttress (shown as a slight convexity or shoulder 
at the left of the peak) is a considerable distance to the east¬ 
ward of the peak, the nearest source of the material, and quite 
out of range of rolling material, even were the circ not present. 
Of all the occurrences thus far discovered, those shown in 
Fig. 1 are most susceptible of explanation under the assumed 
hypothesis (survival of talus) since the bluff top above carries 
a thick capping of limestone. But since it is obviously im¬ 
possible that talus should have formed aggregations of such 
form as are now presented, the hypothesis assumes that the de¬ 
posit was once continuous along the bluff side, and that the circs 
have—in large part at least—been excavated in such deposits. 
There are however two fatal objections to this assumption a. 
The composition of the deposits is radically different from that 
of normal talus of the same horizon; and b, it necessitates the 
assumption that here existed a continuous shelf some 300' above 
the river, of such width and slope as to give support to talus de¬ 
posits 15' to 25' in thickness. Such a shelf in such a position 
would however be a topographic anomaly, at least in this region. 
In classifying the occurrences according to topographic asso¬ 
ciation, I noted one on ridges near the opening of a small 
valley. I have sometimes spoken of these ridges as but¬ 
tresses, but they have no relation either in form or origin to 
those above referred to in connection with circs. They are 
offsets from the sides of the valley at its outer end, of about 
the same hight, and so placed that were the notch between 
them closed there would result an almost direct ridge from 
side to side. The valley itself shows the well rounded ampi- 
theatre like contours characteristic of maturity both in the 
short, and in the digital ends of the longer valleys of the 
region, the ridges alone breaking into its normal symmetry 
of form. As topographic features they are a decided 
anomaly. They would be easily explained if we could 
assume the existence of a much harder ledge of rock cross¬ 
ing the valley, but in this region' of undisturbed rocks, and 
in the upper part of the Potsdam, the explanation fails. Xo 
