IKOQUOIS PLANE 243 



order to establish the channel as we find it. For reasons that will appear 

 later in this writing, it seems quite certain that there was no appreciable 

 land uplift in the Covey district, while the Covey outlet was effective; 

 but any considerable rise would have thrown the outflow back on the 

 Rome outlet. These questions are subjects for future intensive study. 

 But even now it seems clear that there could not have been great differ- 

 ence between the altitudes of the two outlets, and that the highest beach 

 south of the Rome isobase and the latest beach in all the basin correlates 

 with the Covey outlet and practically with the Rome outlet also. When 

 the former is described and illustrated, it will be seen that it carried the 

 pre-Saint Lawrence flood long enough to establish its shoreline. 



The Covey outflow persisted while the front of the glacier rested 

 against the north and east faces of Covey Hill at a height above 1,030 

 feet. While the ice-front was receding, on the north-facing slope, from 

 1,030 down to 740 feet, the sub-Iroquois outflow was scouring the slope 

 between those altitudes. In horizontal distance on the northeast face of 

 Covey Hill the drop from 1,030 to 740 feet is only about one-half mile. 

 How long time did this bit of ice-front recession consume? i\.nd how 

 much uplift of the district occurred during this episode ? Relatively, the 

 time must have been brief, and if there was any rising of the land at all 

 it was so small that we may consider it negligible in our calculations. 



Altitudes and warping in the Ontario Basin 



It is believed that the time interval between the abandonment of the 

 Covey outlet and the establishment of the marine level in the Ontario 

 basin was relatively so short that the land uplift at Covey outlet during 

 that brief time is negligible as compared with the total uplift. With this 

 admission, it follows that the vertical interval everywhere in the Ontario- 

 Saint Lawrence depression between the Iroquois and the marine planes 

 is 290 feet (1,030 minus 740). This uniform interval throughout the 

 basin provides us with a master key to the amount of deformation during 

 two time episodes — Glacial (Iroquois) time and post-Glacia] (post-Iro- 

 quois) time. Wherever in the Lake Iroquois area we can find the alti- 

 tude of either the Iroquois or the marine plane, we can calculate the other 

 one. The marine or sealevel altitude in the Ontario basin represents the 

 amount of post-Iroquois uplift. By subtracting this from the total up- 

 lift, as indicated in the map of isobases, we determine, for that point in 

 space, the amount of uplift previous to the extinction of Iroquois, which 

 is Glacial time for New York; and the total uplift, the isobasal value, 

 subtracted from the present altitude of the point, gives us the height of 

 that point above the ocean before the uplifting began. 



