658 THOMAS L. WATSON 
erosion. Scarcely any doubt exists against 
the large share of these tarns having resulted 
directly from differential ice scouring along 
the line of weaker rocks. In other cases, 
however, the basins have been more or less 
modified by the ice advance, which served 
to remove the preglacial decay, resulting in 
some instances, ina probable deepening from 
this cause. 
Evidence has been brought forward by 
others, proving that not all trace of minor 
preglacial form was destroyed by the ice 
advance over portions of this and the Baffin 
land coast. Furthermore, that in itsadvance, 
all the preglacial decay was not removed, 
but that a somewhat roughened and irregu- 
lar surface resulted from such action, mostly 
along the lines of rock weakness. To the 
combined action, therefore, of differential 
preglacial weathering and ice erosion, along 
the lines of weak structure, are due most, if 
not all, of the group of highland lakes. 
Concerning the origin of this type of lake 
along the Greenland coast and other simi- 
larly glaciated lands in the arctic latitudes 
Professor Tarr says :* 
It is noticeable near Cumberland Sound, as well 
as in Turnavik, and in Hudson’s Strait, and indeed 
in Greenland, that there are many basins of small 
size, surrounded entirely by rock. While some of 
these have no doubt been scoured out by differential 
ice erosion, the position of many of them along the 
lines of weaker rocks, indicates that they represent 
differential preglacial weathering. The advance of 
the ice in these cases has served to remove the 
WDARR) Re) (St:@ Amer. iGeolaarso7.) Vols XOX nip ps 
195, 196. 
apiice 
East 
Lake bottom 
West 
ke 
Sea level 
—— 
Lake ‘bottom 
Sea level 
bone bottom 
Profile of valley marked AB 
Scale # =foo inches. 
rs ‘ 
Fi 
