218 J. W. SPENCER POSTGLACIAL EARTH-MOVEMENTS 



reached its maximum along a line joining the foci, or that the axis of the 

 maximum regional uplift was meridional and located along the eastern end of 

 Lake Ontario, increasing in amount until near 'the height of land,' and thence 

 with a diminishing ratio, or even depression, toward the north. Still it is 

 hardly probable that the increasing ratio is constant, as there are local trans- 

 verse folds on both sides of the Ontario basin. At any rate, it is in the region 

 southeast of James Bay that the maximum differential elevation of the earth's 

 crust, which involved the Iroquois Beach, is to be found." 



While this was written in the pioneering days of our lake studies, it 

 has nevertheless been the key to subsequent researches. Since then Gil- 

 bert, De Geer, Taylor, Leverett, and, more completely, Goldthwait, have 

 shown the deformation by isobars in place of my triangles, which last 

 method has been used by Coleman. Goldthwart/s extension of the isobars 

 westward to Lake Algonquin is an admirable addition to the subject, 

 which stimulates further research. Each method has its advantages. 

 The isobars show the lines of equal rise, while the triangles give the 

 mean rate of deformation in different localities, and in addition they 

 suggest the amount of change beyond the points where measurable data 

 are found. The deformation is now determined eastward nearly to Lake 

 Champlain and Montreal. 



Iroquois Water North of the Adirondack^ 



In my original surveys of the Iroquois Beach, the shoreline was traced 

 to a point 4 miles east of Watertown, New York, beyond which the beach 

 was interrupted in the broken country. To this point all of my determi- 

 nations of elevation were made by leveling. To the eastward, fragments 

 of beaches were found, the elevations of which were determined by the 

 aneroid, as at Natural Bridge, Pitcairn, and Fine. Although their posi- 

 tions appeared rather high, I regarded them as the equivalent of the 

 Iroquois shore, thus making the eastern rise seem excessive; but they 

 indicated open water north of the Adirondacks. This was one of the 

 features which caused me to oppose the hypothesis of glacial dams. Such 

 dams had been located by the advocates of the hypothesis at Cleveland, 

 Adams Center, and Crittenden, but the further survey of the beaches 

 showed that they continued beyond these points, which thus cast addi- 

 tional doubt on the theory. Another objection was presented by the fact 

 that glacial lakes would not remain long at one level, with the water of 

 large streams flowing across ice-barriers; but this objection has been 

 partly overcome by the finding of other spillways passing through rock 

 or earth-bound channels in place of across icy barriers. 





