Upham.] 
236 
[April 17, 
modified drift occur in the banded part of the till, which is nearly 
like the remainder of the extensive deposits of till in this section, 
excepting that it has somewhat more sandy and porous layers al- 
ternating with somewhat more clayey and therefore impervious lay- 
ers, the latter being noticeable because they retain the moisture 
more persistently and have a slightly darker color. But no defin- 
ite line of demarcation separates these layers, there being instead 
a gradual change which occupies a thickness of several inches. 
Nor is the contrast so distinctly seen in examining the section 
near its base, or in climbing up for closer inspection, as at a dis- 
tance of several rods where the small difference in color is better 
displayed in the wider view. Boulders and gravel are indiscrim- 
inately mingled through the whole deposit, which is the ordinary 
boulder-clay or till ; and these alternations in the proportions of 
clay seem probably to be attributable to the slightly varying con- 
ditions of alternating summer and winter, affecting the rate of mo- 
tion of the ice-sheet, its power to erode drift elsewhere, and its 
tendency to deposit its ground moraine on the surface of this drum- 
lin. If this is the true explanation, the yearly addition of till to 
that part of the section averaged two or two and a half feet, and the 
accumulation of the entire drumlin of Third Cliff required probably 
not more than twenty-five or thirty years. 1 Again, in the till over- 
lying the south end of the modified drift of this section such band- 
ing is faintly developed in two or three layers (e) for a length of 
fifty feet or more at an elevation about 40 feet above the sea and 
15 feet below the surface. But no trace of this structure was seen 
in the other sections on the east shore of Scituate. 
Though descriptions of this structure in deposits of till have not 
previously been published, so far as I am able to learn, and though 
apparently it is not found in the drumlins of New Hampshire and 
of northeastern Massachusetts, nor even of the vicinity of Boston, 
excepting within close proximity to the sea, it is yet frequently ob- 
servable in the drumlins of the islands of Boston Harbor. For ex- 
ample, it is finely developed in the cliff of till forming the northeast 
end of Peddock’s Island, where five or six such bands are separated 
1 Similar indications of the rate of annual increase in deposits of modified drift are 
found by the writer in the valley of the Minnesota river at Jordan, Carver and Chaska, 
Minn. (Proc. Am. Assoc, for the Adv. of Science, vol. xxxii, 1883, p. 225; Am. Jour. 
Sci., ill, vol. xxvii, p. 106, Feb., 1884; and Geology of Minnesota, vol. ii, 1888, pp. 131, 
144), and by Prof. B. K. Emerson in-the Connecticut valley at Northampton, Massachu- 
setts (Am. Jour. Sci., in, vol. xxxiv, pp. 404-5, Nov., 1887). 
