influencp: of ice erosion 



183 



of decayed rock proves the ineffectiveness of ice erosion. The movement 

 of the ice was directly across this depression^ and hence not conducive to 

 erosion. This case stands out in marked contrast to the area of vigorous 

 ice erosion immediately westward along the Hudson-Schroon rivers. 



That ice erosion was more or less effective in lowering the pre-Glacial 

 divide at Stony Creek seems certain. The direction of ice-flow was almost 

 exactly parallel to the present direction of the gorge, thus decidedly 

 favoring erosion. Also the cutting power was increased because of the 

 great depth of ice due to its concentration in this the lowest portion of 

 the broad general depression of the northern part of the Luzerne quad- 

 rangle. How much of the depth of the gorge is due to ice erosion can not 

 be stated. 



The Lake George depression was doubtless considerably deepened by ice 

 erosion due to the passage of the deep, concentrated ice of the Champlain- 

 Mohawk lobe (see below). The comparatively weak Paleozoic rocks along 

 the fault in the southern portion of this depression must have yielded 

 pretty readily, and hence the pre-Glacial channel of the Hudson along 

 here was doubtless considerably lowered by ice erosion. Thus the present 

 brook, which empties into Lake George and which occupies the channel 

 between Warrensburg and the lake, is much swifter than was the pre- 

 Glacial Hudson along this course. 



CAUSE OF PASSAGE OF THE HUDSON OVER THE STONY CREEK DIVIDE 



While it may be possible that ice erosion alone was sufficient to cut 

 down the Stony Creek divide so as to allow the passage of the Hudson 

 after the withdrawal of the ice-sheet, this seems highly improbable, and, 

 at least, there is no positive proof for such a belief. However, it is now 

 well established by the early work of Chamberlin, and by the more recent 

 work of Brigham^ and others, that during both the advance and retreat 

 of the ice a distinct lobe occupied the Champlain-Lake George depression 

 and extended around into the Mohawk Valley. Thus, when the Lake 

 George ice-lobe was still present, the pre-Glacial course of the Hudson 

 was completely blocked and the Hudson-Schroon Eiver drainage imme- 

 diately to the west was forced to take a new direction. The natural 

 passageway for this drainage was over the Stony Creek divide, which had 

 already been somewhat lowered by ice erosion. If there was more than 

 one advance and retreat of the ice, as strongly suggestive evidence (given 

 below) seems to indicate, there may well have been considerable gorge 

 cutting by stream erosion during inter-Glacial time, and in this case the 



5 "The MohaM^k glacial lobe," a paper read at the Pittsburgh meeting of the Geological 

 Society of America, 1910. 



