POSTGLACIAL FEATURES OF THE UPPER HUDSON VALLEY 1 3 



elevated sand plain north of Ballston Spa was built somewhat 

 earlier by the glacial Hudson through the Kayaderosseras valley. 

 From study of the Pleistocene waters in their relation to the land 

 uplift the writer believes that the Hudson was in its work of delta- 

 building at Glens Falls when the Iromohawk was forming the lower 

 Saratoga plains. 



EFFECT OF LAND TILTING 



It has been stated that the Iromohawk was diverted into north- 

 ward flow, toward Saratoga, by the obstruction of its own delta 

 deposits on the south and east, as the latter were lifted out of the 

 marine waters. Probably there was another cause. It appears that 

 the land uplift was by a wave movement, progressive from south to 

 north, subsequent to the removal of the ice from th.e rising district, 

 From which it would appear that the uplifting at Saratoga to equality 

 with Schenectady was somewhat tardy. This difference in height 

 would be small, in the i8 miles^ but might have some effect. The 

 chief and unquestioned factor, however, is the differential uplift. 

 The gradient of the uplifted marine plane is in this district 2.4 feet 

 a mile. This makes a difference between Alplaus, the point of latest 

 diversion, and East Line, the point of trifurcation of the river, of 

 22 feet. This means that East Line was originally 22 feet lower 

 relative to Alplaus than it is today. Saratoga was 100 feet lower 

 than Schenectady, and now, after the tilting uplift, is 50 feet lower. 



The Ballston Lake channel is today horizontal, 300 feet at each 

 end. The south (upper) portion of the ancient channel has been 

 cut away by the intrenching of Alplaus creek, graded to the Mohawk. 

 It is apparent that the Iromohawk in the northward flow had sufficient 

 fall to have kept that path unless some outside force intervened. 

 The differential north-uplift supplied the interference. The north- 

 ward flow was weakened and discouraged, and was diverted from the 

 Ballston Lake channel into the present narrow channel eastward 

 toward Cohoes. S toller referred the diversion of flow to the more 

 rapid downcutting of the present channel at Rexford Fiats and 

 Aqueduct. But the constriction of the channel at Aqueduct and at 

 Cohoes indicates that this course was mostly cut by the present 

 diminished stream and not by any long-time flow of the great pre- 

 decessor of the St Lawrence. 



As to relative time and altitude of the eastward diversion of flow 

 we have some data. The Maltaville distributary made channels in 



