518 J. H. STOLLER HISTORY OF MOHAWK-HUDSON REGION 



rock depression continues easterly along the broad valley, followed by 

 Anthony Kill, to the Hudson Valley at Mechanic ville. 



Whether the rock depression in which Saratoga Lake lies is continuous 

 with that of Eound Lake can not be determined by surface inspection 

 because of the mass of Pleistocene clays and sands (Lake Albany de- 

 posits) that occupies the three-mile interval between the two lakes. 



Ballston Lake, as stated above, occupies a depression in the bottom of 

 the Ballston rock channel. Its surface stands at 285 feet elevation, or 

 about 15 feet below the general level of the floor of the rock channel. 



The outstanding physiographic features, about which there is no ques- 

 tion, are an old rock valley at 300 feet elevation (the Ballston Channel) 

 and other rock depressions (perhaps forming a rock valley) a few miles 

 eastward from the former and at a level more than 100 feet lower. These 

 rock-rimmed depressions now lie at the bottom of broader depressions, 

 the slopes of which consist of Pleistocene deposits, for the most part the 

 clays and sands which were laid down in Lake Albany. 



In mapping the Pleistocene deposits of the region, we find evidence of 

 broad watercourses extending from the Ballston Channel to the depres- 

 sions in which Saratoga Lake and Eound Lake lie and beyond to the 

 valley of the Hudson. In these watercourses the clay and sand deposits 

 are largely swept away and worn rock surfaces are exposed; or where till 

 occurs the finer materials have been largely removed, leaving an eroded 

 surface often scattered with numerous boulders. 



There are three such watercourses diverging from the Ballston Channel 

 in the area about East Line, north of Ballston Lake. Of these, one ex- 

 tends northerly, following the line of the old channel, as far as east of 

 Ballston Spa, where it broadens and turns eastward to Saratoga Lake. A 

 second glacial watercourse extends northeasterly from the locality of East 

 Line and joins the former course about the southern end of Saratoga 

 Lake. The third extends southeasterly to the Round Lake depression. 



In considering the development of these watercourses, it is to be borne 

 in mind that the subsidence of the Lake xAlbany waters took place by 

 degrees. When the lake was at its full development its waters stood at 

 about 360 feet at Schenectady, as shown by the level of the great sand- 

 plain, representing delta deposits, extending southeastward from Sche- 

 nectady. As soon as the Iroquois-Mohawk currents were deflected into 

 the Ballston Channel they discharged into the lake in the region south 

 and east of Ballston, transferring the work of delta-building to that quar- 

 ter of the lake. When the next stage of recession of the lake waters super- 



