GOLDTHWAIT: SAND PLAINS OF GLACIAL LAKE SUDBURY. . 281 
built high above the level of the lowest col, at a time when the outlet 
was temporarily blocked by ice and the lake-level raised, never could 
lobes be built at a level below the level of the col, for the lake-level ' 
could not sink lower than that. This point is useful as a test between 
the ice-dam and tilting hypotheses; for by tilting extraordinarily low 
lobes may be produced. Haphazard grouping of levels, then, and the 
absence of lobes lower than the level of the lowest col, are what we 
should expect from the ice-dam hypothesis. 
Tilting in New England presumable from Other Evidence. 
Everywhere that glaciated regions have been studied in detail there 
is evidence of postglacial tilting. DeGeer’s work on the raised shore- 
lines of Scandinavia prove that there, at least, the profound postglacial 
movements were confined almost perfectly to the area that had been 
covered by the ice-sheet, as if the earth’s crust had sunk beneath the 
weight of the ice, to rise again when it withdrew (a, 66; b, 25). 
In Lake Agassiz, the present slanting attitude of the old shore-lines is 
believed by Upham to be almost entirely the result of a rise of the land 
when the ice left it. These tilted shore-lines are exhaustively described 
and the cause of tilting thoroughly discussed in the monograph on Lake 
Agassiz (Upham, d). The rate of tilting is usually only about a foot 
per mile, but towards the northern part of the region it becomes nearly 
three feet per mile (d, 426, 474-486). 
In the Great Lakes region, Taylor has traced the tilted water-planes 
of the lakes of late glacial times, and has worked out the rate of tilting. 
In the case of Lake Nipissing, this tilt rate is found to be only about 
seven inches to the mile; but in other cases it is much higher. The 
tilting measures most in a direction north 25° east (c, 652). 
The work of Gilbert and Spencer on the shore-lines of Lake Iroquois 
and Lake Warren, the large temporary lakes in the region of Lake 
Ontario, show that the withdrawal of the ice from that district was ac- 
companied by a very considerable rise of the land, by which the horizon- 
tal beaches were tilted into a slanting position. About Lake Ontario 
the shore-lines of extinct Lake Iroquois are tilted at an average rate of 
three and a half feet to the mile (Gilbert, 603). In the vicinity of 
Cape Rutland, north of Syracuse, the rate is about five feet to the mile 
(Spencer, 128). 
In western New York, Fairchild finds that the direction of great- 
est tilt is between north 17° east and north 20° east (e), indi- 
cating “that the isobases of the greater area are curving lines with 
