50 NEW YORK STATE MUSEUM 



Each of the three high peaks making up the group known as the 

 Three Sisters south of Thurman station seems to show interesting 

 and rather notable effects of ice erosion. Each has a very steep to 

 precipitous south face of sohd rock hundreds of* feet high, and each 

 has a much longer more gradual northern slope (see plates 5 and 

 6), The unnamed peak shows this structure best of all. The 

 northern flank of each carries considerable glacial drift. Evidently 

 these peaks were so situated that the southward moving ice sheet 

 flowed against and over them with unusual force, wearing down 

 their northern slopes by abrasion and plucking of joint blocks, while 

 on the sheltered lee side of each only the relatively loose joint 

 blocks and talus were rather gently cleaned away by the ice. The 

 contour lines do not adequately express the shapes of these peaks. 

 With thinning of the glacier and weakening of its power, the 

 tendency was to deposit morainic material on the northern flanks. 



Among various other mountain peaks and hills whose shapes are 

 probably due to the same causes as the Three Sisters are: the 

 mountain with precipitous face hundreds of feet high just north 

 of Thurman station, and the hill (altitude 1600 feet) 2 miles north 

 of Hadley hill. The southern face of neither of these is properly 

 shown by the contours on the map. 



Of very special interest are the two hills just north and northwest 

 of Luzerne. Each of these is over one-half of a mile long and 200 

 feet high. Here again the map contours fail to express properly 

 the profiles of the hills. Both hills are of the same shape and origin, 

 but the eastern one is the better example. A good idea of the more 

 easterly one may be gained from plate 8B. The southern one-fourth 

 of this hill consists of practically solid rock with a precipitous 

 southern face 200 feet high. On the northern side the hill slopes 

 downward gradually for 200 feet with remarkable uniformity for 

 one-third of a mile to the level of the surrounding sand plain. In 

 outward form this hill is like a typical drumlin, but in reverse posi- 

 tion in regard to the direction of ice movement which was here 

 south 5 degrees east. Evidently the ice here rode over a high rock 

 knob, wearing down its northern side and simply removing talus 

 and loose joint blocks from its protected (southern) lee side. When 

 the ice became thin and too weak to erode, during the waning of 

 the glacier, it began to deposit morainic material on the northern 

 side of the hill, plastering it on with a remarkable degree of 

 uniformity. 



