8 NEW YORK STATE MUSEUM 



which lies Round lake. The floor of this depression is largely cov- 

 ered with materials of Glacial age but on the slopes, at their lower 

 levels, there are frequent exposures of rock. Rock appears only 

 a few feet above the level of the lake on the northern side where 

 the rock-valley, through which the outlet stream of Ballston lake 

 flows, opens into the depression. Exposures of rock appear at sev- 

 eral places on the road, recently macadamized, running southeasterly 

 from Maltaville. On the south side of the depression, rock is seen 

 on the banks of the stream below the pond at Usher. 



Concerning this depression and that in which lies Saratoga lake, 

 four miles to the north, with an elevation of 204 feet, Woodworth 

 says : " It seems probable that Round and Saratoga lakes are un- 

 filled depressions marking the site of an old valley west of the 

 present Hudson gorge." J. H. Cook, in a paper read before the 

 American Association for the Advancement of Science in 1908, 

 gives additional facts indicating that an old rock-channel, now cov- 

 ered, extends southerly from the Round lake region, intersecting 

 the valley of the Mohawk below Vischer Ferry. 



THE GLENVILLE ROCK BASIN 



I give this name to the extensive depressed area bounded to the 

 west by the slope of the Glenville hills and on the north and east by 

 the more gradual and broken slope of the Charlton hills. The basin 

 is drained by two streams : Alplaus kill, which Hes at the base of 

 the Charlton slope, emerging from the basin at High Mills where 

 it enters a gorge that opens into the Ballston channel ; and a creek, 

 unnamed on the topographic sheet, that skirts the base of the Glen- 

 ville hills and joins the Alplaus creek in its course through the 

 southern end of the Ballston channel. Both these streams receive 

 small tributaries. One of these marks the extension of the basin 

 to the south where it opens into the Mohawk channel. 



For the most part the rock underlying this basin has but a thin 

 covering of soil. The Alplaus kill traverses lacustrine deposits, as 

 will be later explained, but the streams draining the rest of the basin 

 show frequent exposures of rock. 



