GEOLOGY OF THE NORTH CREEK QUADRANGLE 6/ 



against the much higher mountains which are arranged along the 

 eastern side of the adjoining Thirteenth Lake sheet. 



Some of the striae are so situated in valleys as to suggest that, 

 locally at least, the ice currents followed the valleys, but many 

 others are situated wholly without reference to the topography. 

 Among the best examples of striae which are significant as proving 

 that the general ice movement was irrespective of even the major 

 topographic features are the following: just north of ]Mud pond 

 and immediately south of the Huckleberry-Crane-Little mountain 

 masses, thus showing the retention of the southward course in 

 spite of those mountains ; immediately under the steep fault scarp 

 on the east side of Loon lake ; at the north bases of Pine and Gage 

 mountains, showing that the ice current headed straight for those 

 high mountains; and on the hilltop just northwest of Johnsburg: 

 where the ice left its record after having plowed diagonally up 

 the hill for an altitude of several hundred feet instead of following 

 the valley. 



The great depth of ice over the region is proved by the frequent 

 occurrence of drift boulders even on the high mountains, the high 

 altitudes of some of the striae, and the glacial lake on Crane moun- 

 tain. Some of the striae at considerable altitudes are as follows : 

 north of Mud pond (southwest corner) at nearly 2000 feet; 2 

 miles east of Cherry ridge at from 1500 to 1600 feet; west base of 

 No. 9 mountain at 1600 feet; 2^ miles southwest of Johnsburg; 

 at 1550 feet; on the side of Stockton mountain at over 1500 feet; 

 and one-half of a mile northwest of Johnsburg on a hilltop at 1480 

 feet. On this basis, granting a fairly level ice surface, the depth 

 of ice must have been at least looo feet or the difference between 

 these highest striae and the Hudson river to the east. However, 

 the presence of the glacial lake with drift dam well up on Crane 

 mountain, and at an altitude of 2620 feet, shows that the ice was 

 deep enough to cover the mountain that high up at least. Accord- 

 ing to this the ice must have been at least 1500 feet deep in the 

 valley just north of Thurman and fully 2000 feet deej) in the 

 valley of the Hudson river. 



ICE EROSION 



To say the least, ice erosion was very effective in the removal 

 of nearly all j^reglacial soils, decomposed rock, and loose joint 

 blocks. The mountains were swept clean of such materials and left 

 standing as more or less rounded off bare rock ledges, while during 



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