214 BULLETIN OF THE 
study a dozen or more parts of the field in which the evidence as to 
the small amount of glacial wearing is particularly clear. These areas 
are widely scattered, and from the additions which are constantly being 
made to the list it is evident that they are numerous. While this 
essay was in preparation, my assistant, Mr. J. B. Woodworth, discov- 
ered a characteristic field of this nature in the region of hill land, on 
the western border of Rhode Island, where the decayed schistose rocks, 
the decomposition of which evidently occurred in pre-glacial times, have 
not been removed by the action of the ice. At first I was disposed to 
attribute the absence of erosion in these districts to some local arrest of 
the ice movement, but a careful inspection of the localities has generally 
disclosed the existence of areas of hard rock, which bore the normal 
marks of glacial wearing, showing clearly that the ice moved in the 
ordinary manner over the area. I therefore felt compelled to frame 
another hypothesis to account for the arrest of glacial wearing during 
the greater part of the time when the ice sheet lay over the areas in 
question. While I am still in mnch doubt as to the value of these sug- 
gestions which I have to offer, I may say that they have withstood my 
own criticisms and those suggested by several of my fellow students of 
the phenomena for a period of ten years, and it therefore seems well to 
offer them for more extended debate. 
HYPOTHESIS CONCERNING THE CONDITIONS OF CONTINENTAL GLACIERS. 
We have already had occasion in the preceding pages incidentally to 
note the effect of pressure in lowering the freezing point of ice, but it 
appears to me that we have by no means exhausted the considerations 
as to the conditions of deep glaciers which are open to us by the im- 
portant discoveries as to the effects of pressure on ice which were made 
by the brothers Thomson about forty years ago. I propose, therefore, 
to review the matter, with the hope of discovering some explanation of 
the arrest in the wear of the bed rocks which seems to have occurred 
during the time when a thick ice sheet occupied the northern portion of 
this continent. There can be no doubt that pressure melting operates 
in an effective though slight manner even in the superficial portions of 
an ice mass. The phenomena of regelation exhibited when two bits of 
frozen water are pressed together, clearly shows the way, as has often 
been observed, in which the conditions operate, and many other simple 
experiments serve to indicate an action of the same nature. There now 
appears to be little doubt in the minds of those who have inquired into 
