iS93.] [Upham 
moderately slopino; tracts, hut is often from "15 to 20 feet or more 
on tlie drumlins, the color of the till is yellowish gray or buff, while 
at greater depths it is a darker and bluish gray. This difference 
in color is due to progressive weathering, the influence of air and 
water upon the iron contained in the till having changed it in the 
upper part from protoxide combinations to the hydi-ous sesquiox- 
ide. On low tracts the weathering of the till is often limited to 
its comparatively loose englacial portion, but it has generally 
extended beyond into the subglacial till of the drumlins. 
Most instructive variations fronx the usual constitution of the 
drumlins are ))resented where anticlinally stratified beds of 
gravel, sand, and clay or fine silt, form their inner ])art, reaching 
in a dome-shaped accumulation from the base upward to com- 
prise sometimes the greater part of the section, with a deposit of 
till, which may be from a few feet to 25 feet or more in thick 
ness, spread over these beds so as to form the entire surface. 
Among many sections of drumlins observed by me in New 
England, the only examples of this structure are Third and 
F'ourth Cliffs, partially eroded drumlins in Scituate, Mass., on 
the shore of Massachusetts Bay. These rounded, low hills, 
rising respectively about 70 and 60 feet above the sea, consist of 
till upon their Avhole surface and to a depth that varies from 15 
to 25 feet and more, but below include beds of modified drift that 
attain in Third Cliff a thickness of at least from 30 to 48 feet, reach- 
ing to the boulder-strewn shore, and in Fourth Cliff a thickness of 
from 10 to 20 feet, being seen there to be underlain by till and to 
be also in part interbedded with it. 
Generally throughout drift-bearing areas the till, excepting 
where it is accumulated in the hills and knolls of the terminal 
moraines, has a comparatively low and level or moderately un- 
dulating surface. But on certain tracts a large part of the till is 
exceptionally amassed in the drumlins, which stand up very con- 
spicuously as high hills, sometimes occurring plentifully with 
irregular arrangement in groups or belts which may extend from 
20 to 50 miles or more and often have their greatest length in 
j.arallelism with the course of the terminal moraines. Elsewhere 
drumlins are sparingly scattered here and there with intervals of 
several miles between them, this being often observed on the 
borders of their tracts of greatest abundance ; and rarely a single 
typical drumlin, as Pigeon Hill on Cape Ann, may be separated 
many miles from any other like accumulation of till. 
