NEW FACTS AND REDISCUSSION 521 



eludes the northern portion of Saratoga Lake and the valley of Fish Creek 

 for some miles northeastward from the lake. 



Allowing for postglacial deformation, it may be deduced that the sur- 

 face of the Saratoga delta was originally about 50 feet lower than the 

 present plain. That is, it was built at a time when the Lake Albany 

 waters had lowered to that extent, as compared with their highest level, 

 when the Schenectady delta was formed. 



With the further subsidence of the lake waters, a repetition of the 

 previous steps of drainage development ensued. The Saratoga delta be- 

 came land surface and the Iroquois-Mohawk currents cut their way 

 through this emerging surface. The three divisions of the flooded river 

 established at the time of the emergence of the Malta delta were main- 

 tained and their courses were extended through the added areas of land 

 surrounding the shrinking lake. At the same time the currents broad- 

 ened, their channels producing the broad water-swept depressions south 

 and east of the Saratoga plain. 



COVEVILLE DELTA STAGE 



West of the northern end of Saratoga Lake and extending northeasterly 

 west of Fish Creek is a sand-plain at 260-280 feet elevation. The plain 

 is well defined, its margin being a bluff or steep slope, separating it from 

 the lake and its outlet on the east (southeast) and from the eroded tract 

 on the west. The extent is about 2% miles in length and an average of 

 half a mile in width. 



This sand-plain is interpreted as representing a third delta-building 

 stage by the Iroquois-Mohawk, which began at the end of the stage of 

 subsidence of the lake waters that caused the emergence of the Saratoga 

 delta. This sand-plain may probably be correlated with the prain at the 

 same general level developed west of Coveville, referred to below. 



ORIGIN OF SARATOGA LAKE 



We now come to an interesting phase in the drainage history of the 

 Saratoga region. As soon as the subsidence of the Lake Albany waters 

 had proceeded to the extent that the surface of the lake was lower than 

 the rock bottom of the Ballston Channel, the gradients of the several 

 distributing streams were increased. Their waters, escaping from the 

 confines of the Ballston Channel, flowed toward the preglacial rock de- 

 pression a few miles to the east. As the subsidence of the lake waters 

 continued, progressively increasing the fall of the streams, the increased 

 erosive power thus given to the currents enabled them to sweep away the 



