1891.] 
231 
[Upham. 
and the last of the several questions which this paper attempts to 
answer is, Do our modified drift deposits afford evidence of sub- 
glacial drainage in the Champlain epoch, that is, the closing stage 
of the glacial period ? 
Having thus outlined the intended scope of our investigation, 
let us survey the lakes and their bordering gravel, sand, and silt 
deposits which suggest these problems and may reveal how they 
can be solved. 
Lake Walden, formerly called Walden pond, is situated in 
Concord, Mass., beside the Fitchburg railroad, at a distance of 
about fifteen miles, in a direct line, west-northwest of Boston. 
Its low water level is about 152 feet above the sea at the mean 
between low and high tide, and it fluctuates six or seven feet to 
its high water stage, which is reached after a succession of several 
years having slightly more than the average or normal rainfall. 
This lake is endeared to naturalists and all lovers of poetic prose 
by its having been the place of Thoreau’s hermitage in the years 
1845-7; and from his “Walden” portions of the following de- 
scriptive notes are transcribed. Thoreau calls it “a clear and 
deep green well, half a mile long.” Its width is nearly a quarter 
of a mile, and its area at low water is about 61 acres, as stated by 
Thoreau, and at high water probably about 65 acres, as given by 
Shattuck. 1 Low stages of the lake occurred in 1824 and in 
1845-7 ; and high stages about 1830 and in 1852. Last summer, 
on July 23rd, I found the water at or very near its highest level, 
as it overflowed the base of large trees. 
Thoreau’s soundings gave a maximum depth of 102 feet at the 
center of the lake, which would be 108 feet from the high level 
of last summer ; but to obtain the depth of the basin we must add 
the height of 40 to 45 feet from the high water to the surround- 
ing plain. The lake is wholly enclosed by beds of coarse gravel 
and sand, which in some places have an uneven contour of irreg- 
ular knolls and hollows, but mostly are nearly level to distances 
varying from an eighth to three-quarters of a mile from the lake, 
with their surface approximately 200 feet above the sea. On the 
south and west these plains abut upon hills of rock ; but north- 
ward, in which direction they extend farthest, their boundary is 
a sudden descent of about 60 feet to the fertile farming land near 
1 History of the Town of Concord, 1835, p. 200, 
