212 BULLETIN OF THE 



be sot 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 former!}' 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 tlic 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 everj'where more or 

 less modilied, and sometimes very greatly changed, by the erosive work 

 of tlie 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 smaller tril)utaries of the streams, 

 those occupied 'by the lesser permanent brooks, have lost their valleys 

 by the process of glacial ei'osion. 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 I'eview 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 hj'pothesis of even this amount of erosion with the remark- 

 ably well preserved details of the river work in this region. 



The sliirhtness of the wearing which seems to have occurred in North- 

 ern Rhode Island is paralleled at many other points wliich 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 foi-mcd wliere calcific limestones 

 ai-e exposed to long continued weathering. Tliese 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 



