PA BULLETIN OF THE 
be set forth, I have not succeeded in making the amount of the down- 
wearing less than an inch per annum. 
’ The more accurate our knowledge as to the genesis of the topography 
within the ice-worn region becomes, the more clearly is it proved that the 
essential features of the surface are not due, as was formerly supposed, 
to the erosion effected during the Glacial Period, but are to be ascribed 
to the ordinary agents of erosion which operated on this district during 
the pre-glacial ages. Nowhere is this fact more evident than in the dis- 
trict about Iron Hill. The surface of that field still discloses a drainage 
system which in its main features is clearly very ancient. The valleys 
have the normally digitated character which is characteristic of the work 
done by fluid water, and though these depressions are everywhere more or 
less modified, and sometimes very greatly changed, by the erosive work 
of the ice, the type of the topography is truly fluviatile, in this regard 
differing from such characteristically glaciated districts as Labrador, 
Scotland, or Scandinavia. Only the smailer tributaries of the streams, 
those occupied by the lesser permanent brooks, have lost their valleys 
by the process of glacial erosion. Although I have made numerous 
efforts to secure some basis for a quantitative estimate, however imper- 
fect, concerning the amount in depth of the material which was removed 
from this district during the Glacial Period, I have not succeeded in 
obtaining any data deserving consideration here. I can only state the 
general impression made by a review of the topography, which is to the 
effect that the wearing brought about by moving ice cannot have 
amounted to as much as an average of one hundred feet over the region 
within a radius of thirty miles from Iron Hill. It is difficult indeed to 
reconcile the hypothesis of even this amount of erosion with the remark- 
ably well preserved details of the river work in this region. 
The slightness of the wearing which seems to have occurred in North- 
ern Rhode Island is paralleled at many other points which are much 
farther within the boundaries of the great North American glacier. I 
shall note but two instances of the many which I could cite for the 
purpose of showing that the erosive work accomplished during the last 
Glacial Period was at certain points even less than I think it was in 
the neighborhood of Iron Hill. In the region about Pittsfield, Mass., the 
considerable areas of limestone rock there exposed retain the sink-holes, 
or shallow pits, which are normally formed where calcitic limestones 
are exposed to long continued weathering. These depressions have 
been filled with glacial waste, but the pits have evidently lost but little 
of their original depth. In the same region the decayed mica schists 
