348 Tlie AhK'vlean Geologist. iJetemiMT, i893 
My observations of the sections of dnimlins, Ijefore mentioned, 
forming Third and Fonrth Clitfs in Scitnate, Mass., and islands 
in Boston harbor, and the prevailing trends of the drnmlins near 
Boston in parallelism with the latest deflected glacial currents, 
convince me that these hills were somewhat rapidly heaped up. 
beneath the retreating ice-sheet within a few miles back from its 
margin. Peculiar dark bands, evidently representing successive 
stages of deposition, were noted in the till of the northern part 
of Third Clitl'. Their number is seven or eight, each six to twelve 
inches thick, varying from one to three or four feet apart, continu- 
ing separate along an extent of about 200 feet, with no branching 
or inosculation. The portion of the till thus banded has a verti- 
cal width of 15 to 20 feet and a dip of about Ave degrees north- 
ward, being included between 20 and 45 feet above the sea. It 
is more inclined than the overlying surface of the drumlin, which 
is there about 60 to 55 feet above the sea, or than even the steep- 
est slope of the surface farther down. No stratified layers or 
seams of modified drift occur in the banded part of the till, which 
is nearly like the remainder of the extensive deposit of till in 
this section, excepting that it has somewhat more sandy and 
porous layers alternating with somewhat more clayey and there- 
fore impervious layers, the latter being noticeable because the}' 
retain the moisture more persistentl}^ and have a slightly darker 
color. But no definite line of demarcation separates these layers, 
there being instead a gradual change which occupies a thickness 
of several inches. Boulders and gravel are indiscriminately 
mingled through the whole mass, which is the ordinary ])Oulder- 
claj* or till; and these alternations in the proportions of clay seem 
probably attributable to the slightly varying conditions of alter- 
nating summer and winter, affecting the rate of motion of the 
ice- sheet and its tendency to deposit its ground moraine on the 
surface of the drumlin. If this is the true explanation, the 
yearly addition of till to that part of the section averaged 2 or 
2^ feet, and the accumulation of the entire drumlin of Third 
Cliff required probably not more than 25 or 30 years. 
Though such banded structure, approximately parallel with the 
surface, has not been found in the drumlins of New Hampshire 
and inland parts of Massachusetts, nor even of the vicinity of 
Boston, excepting within close proximity to the sea, it is j'et fre- 
quently observable in the drumlins of the islands of Boston liar- 
