The Origin of Drumlins. — Tar'r. 403 
"Professor Davis tells me also that in the southern part of 
the belt of very abundant drumlins in central New York, their 
sections frequently show stratified gravel and sand under- 
lying the till, and that often the relationship of these forma- 
tions is such as to prove that the stratified beds were some- 
what eroded before the accumulation of the till, as by an ad- 
vance of the ice-sheet over a preglacial or interglaeial de- 
posit." 
(b) Assurfred Absence ';/' Boulders. — The absence of abund- 
ant boulders in these drift hills is also appealed to as evidence 
against this theory. In the first place, boulders are not always 
so infrequent as at first sight they appear to be. At times an 
abundance of boulders appear on or in the drumlins. (Jpham* 
states that there are plentiful boulders in the drumlin of Col- 
lege Hill, Medford, Massachusetts, and Johnsonf says that 
there are numerous boulders on the drumlins of central New 
York. For reasons of location and soil, the drumlins, in New 
England at least, have been converted into farms and the 
boulders, which were undoubtedly originally strewn over the 
surface, have in part been incorporated into stone walls and 
foundations for buildings. 
That many and often large boulders occur in drumlins is 
proven, in the Boston Bay region, where the sea has en- 
croached upon them. The sea cliff is faced with boulders at 
its base, and where, as has sometimes happened, the hill has 
been nearly completely destroyed by the waves, there some- 
times exists a line of large boulders marking the drumlin site. 
But, so far as my observations extend, the boulder-strewn 
moraine is the exception rather than the rule. Only where 
peculiar conditions of supply and transportation existed, are 
the boulders numerous. Hence ordinarily, the drumlins. if of 
morainic origin, need not contain a much larger percentage 
of boulders than does ordinary till. In the particularly rocky 
moraine of Cape Ann, Massachusetts, the greater part of tin- 
boulders are on the surface, and these, at the first advance of 
the ice would be swept away. Moreover, if the theory here 
presented is true, such boulders as remained would lie buried 
*Proc. Boston Soc. Nat. Hist., 1889, vol. wiv. p. 237. 
(•Annals, New York Acad. 8ci., L882, vol. u. p. *2~>~>: Trans., New York 
Acad. Xal. Sri.. 1882, vol. I. pp. 77-80. 
