94 NEW YORK STATE MUSEUM 



thicker in the north than in the south, the amount of deformation 

 was greater in the northern part of the State, With the removal of 

 the load by the melting of the ice the land has " sprung " back, thus 

 elevating the surface, tilting the shore-line features of the glacial 

 lakes. It has been shown by Fairchild^ that the character of the 

 postlacustrine uplift was a lifting in the form of a warped plane 

 with the amount of warping greater to the north. The lines of equal 

 uplift since the marine level are inclined west-northwest to the 

 east south-east (20° from the latitude parallels). The zero isobase 

 passes far south of New York City. The 600-foot isobase enters 

 the Lake Placid quadrangle at the very southeast corner of the map. 

 The northeast corner is cut by the 648-foot isobase. These figures 

 give the total uplift for the region since the marine waters occupied 

 the Hudson-Champlain strait. The figure for the amount of tilting 

 for this datum plane in this region, is 2.71 feet a mile taken along a 

 north and south line, or 2.83 feet perpendicular to the isobases. 



Although Fairchild's papers form a very valuable contribution 

 to this subject, there exists some uncertainty as to the character 

 of the uplift, (i) Was the upward movement gradual and uni- 

 form or (2) was it in the nature of a wave or a series of sudden 

 uplifts? The writer believes that the problem will be clarified by 

 the measurement of beaches, deltas etc. situated at higher levels 

 than the marine plain to supplement those mapped at the lower 

 altitudes. The shore phenomena of the lakes above described 

 afford an opportunity to determine the amount of tilt of the land 

 surface, for they furnish a series of datum planes higher than 

 those in the Champlain valley, which was occupied by ice during 

 the entire period that the laikes existed. Fairchild believes that his 

 figures give the total uplift since glacial time. The writer feels, 

 however, that this conclusion is based upon the state of affairs that 

 prevailed during and after the marine stage and overlooks the 

 shore phenomena of higher lake levels. Although accurate meas- 

 urement of the amount of tilt of the lake levels of the Lake Placid 

 quadrangle is an extremely difficult matter (for the chance of 

 error is great), the table given below would indicate that the uplrft 

 was taking place while the ice was melting from the area. 



1 Fairchild, H. L., Pleistocene Uplift o£ New York and Adjacent Ter- 

 ritory, Bui. Geol. Soc. Amer., 27:235-62. Post-glacial Marine Waters in 

 Vermont, Rep't of Vt. State Geol. for 1915,-1916, p. 1-41. 1917. 



