544 THE JOURNAL OF GEOLOGY. 
sloping top. The depth of the submergence at different points 
would depend upon local conditions. 
From data supplied by the other shore features, it seems 
probable that west of Madison, the lake shore corresponded 
approximately with the present elevation of 373 feet, covering 
nearly all of the plain whose outer edge has an altitude of 362—5 
feet; that west of Convent the shore corresponded approxi- 
mately with the present level of 374 feet, the outermost lower 
edge of the plain having an altitude of 356 to 364 feet, and the 
upper edge of 382 feet ; and that at West Summit the former water 
level has a present elevation of 367 feet, whereas at this point the 
outer edge of the plain has an elevation of only 345 to 356 feet, 
rising to about 380 feet at its moraine edge. It is perhaps not 
necessary to suppose that the edge of the plain was developed 
contemporaneously at these several points, or that the level of 
the lake was absolutely constant. 
The subaqueous overwash plain bordering the moraine is a 
very considerable one. Since deposits of this sort may be of 
very rapid construction, a long period is not demanded for its 
growth. 
SHORE FEATURES OF THE INTRA-MORAINIC BASIN. 
The shore features of the intra-morainic portion of the basin 
differ in several important respects from those of the extra- 
morainic basin. These differences are due to the different con- 
ditions which prevailed in the two parts of the basin. The 
intra-morainic part of the basin was occupied by ice for a portion 
of lacustrine time. Its lake history, therefore, must have been 
briefer than that of the extra-morainic portion. In so far as it 
was briefer, its shore features should be less strongly developed 
than those of the extra-morainic portion of the lake. On the 
other hand, since the glacier left thick deposits of sand, gravel, 
and till upon which the waves could readily work, and since an 
enormous amount of loose material was furnished to the lake 
directly by the melting ice, constructional terraces, spits, bars, 
etc., could have been rapidly built under these favoring con- 
