The Ice-Sheet in Narra(jnnsett Bay. — Woodvorth. 163 
time. AVhile an estimnte of this kind must necessarily be 
vague, it serves to give an idea of the flooded character of the 
streams flowing out of the ice. It does not follow, however, 
that the proportions between sediment and volume of water 
discharged in the two cases here compared are to be consid- 
ered equal. The glacial stream was a narrow one, probably 
not over 150 feet wide in its intraglacial course, as is indicat- 
ed by the esker; but it was flowing with a strong current, 
which enabled it to transport cobbles six inches in diameter 
to the head of the delta. 
The esker. The winding broad ridge which joins the Har- 
rington sand-plain on the north is not typical of its class in 
many respects. Rising out of a group of intraglacial depos- 
its or rude kames on the north, this ridge runs southward for 
half a mile with only here and there the steep sides of a typ- 
ical esker.* In general the esker is so wide as to preclude the 
notion of its deposition beneath an arched channel ; and it 
seems probable that it was deposited in a passage open to the 
sky above, contemporaneousl}" with the building up of the 
sand-plain which was being formed outside of the ice. Near 
its junction with the sand-plain the esker turns abruptly to 
the eastward and becomes higher and flat-topped, being sepa- 
rated originally from the sand-plain by a narrow piece of ice 
from 150 to 200 feet wide; thence it turns abruptly south- 
ward and joins the middle of the plain. At the junction the 
esker is deeply notched. 
CoRRELATIOX OF DEPOSITS ON OPPOSITE SiDES OF THE BaY. 
The correlation of deposits made along the line of the ice 
front at any particular stage of retreat is attended with cer- 
tain difficulties even where there is a continuity of deposit 
indicated by a continuous UKu-aine terrace or ice-contact slope 
at the head of sand-plains, since it is not certain that all por- 
tions of the extended series of more or less confluent plains 
were laid down at one time. Accepting, however, general 
continuity of more or less marginally confluent frontal plains 
with occasional moral nal heads as evidence of a given stage 
of retreat, correlation with disconnected deposits of a frontal 
nature may be made by using the following criteria: 
*Some Typical Eskers of southern New England, Proc. Boston Soc. 
Nat. Hist., vol. xxvi, pp. 197-220. 
