GEOLOGY OF MOUNT MARCY 83 



Cause of the Large Amount of Material Available for the 

 Formation of Terraces 



One of the striking features of the glacial geology of the Adiron- 

 dacks is the small amount of true morainal material^ unmodified 

 by water^ as contrasted with the vast quantities of sand and gravel 

 in deltas, terraces etc., when compared with other districts, such as 

 the Catskill mountains. The writer offers the following hypothesis 

 to account for this condition. Fairchild® pictures a vast ring of ice 

 completely surrounding the Adirondacks, isolating them from the 

 rest of the State. It was during this stage that the glacial lakes 

 herein described existed. The great ice sheet undoubtedly destroyed 

 all vegetable life in both the Adirondacks and the Catskills, but in 

 the latter case the ice retreated northward as an irregular edge 

 which allowed vegetable life to follow the ice in its withdrawal. 

 This condition was not possible in the Adirondacks where the ice 

 ring prevented much if any encroachment on the part of plants into 

 the ice deforested area. In the Catskill region the glacial drift was 

 anchored by the roots of newly growing shrubs etc., and thus it was 

 not easily washed by the streams into the standing waters in the 

 valleys below, so that a large amount of the drift still remains on the 

 slopes. On the contrary the glacial debris in the Adirondacks was 

 not anchored and most of it has been carried down into the valley 

 bottoms and there worked over into lake deposits. This has an 

 important bearing upon the flora of the region and the disastrous 

 effects of forest fires on the thinly soil-mantled mountain slopes. 



Summary of the Glacial Lake Succession 



The Mount Marcy quadrangle was situated near the northeast rim 

 of the ring of ice that surrounded and isolated the Adirondack high- 

 lands from the rest of the State, and thus the northward-draining 

 valleys were blocked, preventing the escape of the vast quantities of 

 waters which flooded the district with lakes. These bodies of water, 

 especially at the higher levels, did not leave distinct shore line 

 features, for their outlets were controlled by ice lobes which caused 

 constant or periodic lowering of their surfaces. 



The district covered by the glacial lakes here described can be 

 divided into two sections, the western and the eastern. In all proba- 

 bility the western section was the first to be relieved of ice, thus 



1 Gushing, H. P., N. Y. State Mus. Bui. 115, p. 495- 



2 0gilvie, L. H., Jour. Geol., 10:397-412. 1902. 

 ^Fairchild, H. L., N. Y. State Mus. Bui. 160, pi. 11. 



