122 GF. Wright—Glacial Era in Eastern North America, 
except from three sources: 1st, the wash from the sides; 2d, 
the decay of vegetation which grew within the circumference 
of the rim; 3d, the dust brought by the winds. It is equally 
evident that what is once in cannot get out. 
Now, from the angle of the declivity the original depth of 
the depression can be approximately estimated. If the angle 
be still the same as at first, the first three terms of the propor- 
tion would be 128 : 505 ::48:17%, making the original depth 
elow the present surface of the peat a trifle over 17 5 feet. 
If, however, we suppose the original slant to have been steeper 
and the rim higher we can still see that there must have been 
a limit to the depth. Suppose the rim to have been one-third 
higher and the slant one-third steeper we then would have in 
round numbers the proportion 188 : 68: : 48: 2348, making the 
original depth of the depression nearly 24 feet below the pres- 
ent surface of the peat. From the nature of the material it 18 
impossible that the depression should originally have much 
exceeded that amount. ; 
Accepting this conclusion, the problem is to determine the 
time it would require the agencies mentioned above to fill the 
bottom of this bowl to a depth of twenty-four feet—a cone 
ninety-six feet in diameter at the base and twenty-four feet to 
the apex—which would be equal to a depth of only ezght feet 
over the present surface. ; . 
Let us apply some of the estimates of the date of this period. 
Mr. J. Geikie, following the lead of Mr. Croll and others who 
look to astronomical data alone, supposes that the so-called 
bog only at the rate of one inch in 1,000 years. hile, if we 
* See Geology of New Hampshire, vol. iii, p. 327. 
