264 ANNALS NEW YORK ACADEMY OF SCIENCES 



stone, a thin layer of which outcrops in the Little Catskills near the 

 Hudson River due east from Overlook Mountain. It also appears in the 

 Helderbergs to the northeast. 



One rather unusual variety of metamorphic rock, several pieces of 

 which were found, has been kindly identified by Professor J. F. Kemp 

 of Columbia University, who writes: "It is a type of rock fairly well 

 known in the Adirondacks. It has obviously been pretty well crushed 

 and granulated, but it is a. member of the anorthosite series, which when 

 unchanged has large rectangular crj^stals of labradorite in a mass of 

 small crystals of augite. . . . The rock outcrops at the very head- 

 waters of the Schroon River in North Hudson township and also in the 

 Keene Valley. I think it probably occurs in many other places, where 

 it has not yet been specially observed. ... In Bulletin No. 138 of 

 the New York State Museum, on page 43, under the name of 'The New 

 Pond Localit}^,' you will find a brief description of the rock." 



That both the specimens just referred to are characteristic of the Adi- 

 rondacks, together with the fact that all the metamorphic rocks found 

 are common in those mountains, indicates that most of the foreign ma- 

 terial in these moraines is of Adirondack origin. 6 



Drainage 



Except for a small portion of its eastern slope, Overlook is drained 

 entirely by a single stream, the Saw Kill, which forms a loop, some ten 

 miles or more in length, extending nearly around the mountain (Fig. 1). 

 From its source in Echo Lake at the base of the northeastern ridge, it 

 flows directly southwest through Shady, then east through the Wood- 

 stock Valley to a point directly south of its source. In the course of 

 this loop, the Saw Kill receives the smaller streams which flow from both 

 sides of the Overlook ridge. Owing to the small size of their watersheds, 

 many of these smaller streams are dry during a part of the year. The 

 rainfall is much greater in the spring than at any other season, and this 

 .gives rise to floods which make the erosive power of these streams much 

 greater than it would otherwise be. The floods at this time are greatly 

 increased by the melting of the winter's snow, and there is added the 

 -erosive force of the ice as it breaks up. 



6 These moraines yielded more foreign bowlders than did the ones on the north side 

 -of the district, in the valley of Schoharie Creek, described by J. L. Rich in the Jour- 

 nal of Geology, vol. 14, p. 113, 1906, especially p. 120. Mr. Rich found but one bowlder 

 of gneiss. It may be that later glacial action, radiating from local centers, had con- 

 cealed earlier bowlders, brought in from the north. Mr. Rich's paper has also some 

 general comments on the movement of the continental glacier, and, at the outset, upon 

 ^he present conditions of rainfall. 



