ALTITUDES AND WARPING IN THE ONTARIO BASIN 245 



the ancient stream head is about 430 feet. Hence the initial altitude of 

 that point would be 110 feet minus 30, or 80 feet. But this must not be 

 regarded as the height of the divide and channel head in pre-Iroquois 

 time, for it is quite certain that the Home district has been buried under 

 delta filling by the glacial drainage from the north (125), and that the 

 original land surface was much below 80 feet altitude. It is thought that 

 the earliest control of glacial stream-flow was at Little Falls, 36 miles 

 southeast of Rome. 



Three classes of figures in the table are derived figures — those for the 

 two periods of land uplift and those for the amount of flooding by 

 Iroquois waters. These are all based on (1) the fixed vertical interval 

 between the Iroquois and Gilbert Gulf planes and (2) the isobases of 

 total uplift, taken in multiples of 5 feet. The first of these basic ele- 

 ments can not be seriously changed, and any possible change will affect 

 all stations alike. Any modification of the isobases will change the de- 

 rived figures locally. However, with all reasonable allowance for errors, 

 the data show striking coherence and unity and close agreement with all 

 present knowledge and philosophy. 



Outlet Control — Splitting of Beaches 



The altitude of the water surface of Lake Iroquois was controlled by 

 the height of 'the outlet, which, up to the closing episode, was at Borne. 

 It appears that Borne had the greatest amount of uplift during Iroquois 

 time of any point in the basin and was probably the point that was earliest 

 in an area of rising land. There may be suggestion of detrital or delta 

 filling at the outlet to account for some part of the uplifting at Borne. 

 Heavy glacial drainage from the north poured vast quantity of detritus 

 into the Mohawk Valley between Borne and Little Falls during much of 

 the lifetime of Iroquois. (For discussion of this see 116, page 34; page 

 38.) It seems probable, however, that the great Glaciomohawk Biver and 

 its successor, the Iromohawk, were not effectively dammed by the tribu- 

 tary filling to any greater extent than to establish sufficient grade over 

 the filling that perhaps extended to the rock channel at Little Falls. The 

 point of outflow or head of the river flow may have shifted westward, 

 with some increase in height; but to whatever amount the Iroquois plane 

 was raised by choking of the Borne outlet, it simply reduces by that much 

 the 180 feet of glacial lifting at that point without in any way affecting 

 the figures for any other locality. The calculations in the table are based 

 on the water planes, and the cause of changes in the Iroquois level does 

 not modify the consequences of such changes, 



