242 H. L. FAIRCHILD PLEISTOCENE UPLIFT OP NEW YORK 



It is possible that the gradient of the warped surface may decrease 

 north of New York, and that in the Champlain Valley we have the 

 steepest portion of the upslope. Precise determination of the summit 

 features in the north edge of Vermont, New Hampshire, Maine, and east- 

 ward will throw light on this problem. For several reasons which may 

 not be discussed here, the inscriptions left by the highest waters may be 

 very weak and difficult to trace, but the common mistake should be 

 avoided of regarding the upper conspicuous features as necessarily the 

 summit level. 



Iroquois Plane 



In the Hudson-Champlain Valley the marine plane is shown by the 

 isobases, but not in the Saint Lawrence and Ontario basin. In the south 

 part of the latter area considerable rise occurred before the sealevel waters 

 were admitted. The isobases in this area represent not only the later 

 uplift out of the sealevel waters, but also the rise during the previous 

 episode, the life of Lake Iroquois. In the relation of the Iroquois to the 

 marine level is found the key to very interesting facts. 



As far north as the Watertown district the Iroquois shore has long 

 been known, being traced and measured by Spencer (43) and Gilbert (36) 

 and in later years by the writer (114). In recent years Ohadwick and 

 the writer have located Iroquois beaches at several points to the northeast, 

 and we now have approximate altitudes of the shoreline clear to Covey 

 hollow, the second and final outlet of the ancient lake. The Chateaugay 

 and Churubusco sheets of the topographic maps cover the last 20 miles 

 of the shoreline in New York, while the remaining 3 miles lie in Canada, 

 covered by the Chateaugay sheet of the Canadian government. Very 

 definite features are found close to the boundary line, at 1,025 feet, and 

 the water surface at Covey outlet is regarded as 1,030 feet. 



The relation in altitude of the two outlets of Iroquois, Pome and 

 Covey, was very close, if not practically identical. If the waters under 

 control by the Pome outlet reached the Covey Pass decidedly higher than 

 the latter, we should expect some record of river flow on the south slope 

 of the pass, but such has not been found. Moreover, in such case a drop 

 in the water level should be recorded in the beaches of the lake shore; 

 but the beach along the south shore and west end of the basin is a unit 

 and seems to have been formed in rising water. It is barely possible that' 

 the control of the earliest flow through the Covey Pass was not at the 

 pass, but around on the east side of the highland, in the region of the 

 Altonabare rocks. It is probable that the Covey Valley originally held 

 some filling of glacial drift which the Iroquois outflow had to remove in 





