﻿128 NEW YORK STATE MUSEUM 



on the Alexandria sheet, as we have just seen. This parallel, 

 but northerly-flowing Theresa valley plainly heads several miles 

 south of the original line of the divide, in other words has 

 pushed it south out of line by headward cutting of its valley. 

 Its ability to do this was no doubt conditioned upon the weak 

 resistance of the Grenville limestone belt there. Once the Pots- 

 dam was cut through, rapid headward cutting of the stream would 

 be possible. From the present valley head a shallow valley runs 

 southwest to Perch lake, and it seems clear that formerly this 

 valley headed along the old divide, and was diverted, bit by bit, 

 by the more advantageously situated stream flowing the other 

 way. The minor tributary valleys from the east and west, 

 between Theresa and the north margin of the sheet, are southerly 

 trending valleys, southeast or southwest, and hence adjusted to 

 a southerly, rather than a northerly flowing stream. The north- 

 erly flowing stream slowly captured and reversed the headwaters 

 of the south stream, extending its capture through a distance of 

 from 4 to 5 miles. 



Northeastward from Theresa are a number of valleys heading 

 sharply against the Potsdam mass which there forms the divide, 

 and leading away from it to the southwest. These are located on 

 belts of Grenville limestone, or of weak schist, and therefore are 

 broader and less ravinelike than most of such valleys in the dis- 

 trict. They are, however, comparatively narrow, distinctly rock 

 walled, and with present flat-bottomed floors owing to drift 

 deposits. 



Here, in the northeast corner of the Theresa sheet, the divide 

 runs off our maps to the east, and with maps of that district 

 not yet available, its further course can not be traced. It, today, 

 rises steadily in altitude in that direction, and is, as in Tertiary 

 times, the divide between waters flowing north to the St Law- 

 rence and west to the Ontario valley. 



The Indian river of today, from Theresa south to the great 

 bend north of Evans Mills, is flowing in reversed direction 

 through what was then the valley of a small stream heading 

 near Theresa and flowing south. Wilson's view is that at the 

 bend it was tributary to a southwest stream, occupying the 

 valley now followed by Indian river above the bend; and that 

 their combined waters flowed south through the present West 

 creek valley to the Black river. With our disbelief in the pres- 

 ence of the Black river there at that time, coupled with the fact 

 that the West creek valley seems both to widen, and to deepen, 



