[892.] 
481 
[Davis. 
tained on or in the ice and delivered as it melted away, 'thus 
forming the loose scattered upper till, well studied byUpham; 
but where glacial streams flowed from the ice out upon the open 
front country, there may there have concentrated upon a small sur- 
face the material that their waters had gathered from a much larger 
area on or under the ice. Such streams may have been larger 
than their modern representatives, partly because of the addition 
of ice-water to the ordinary local and immediate supply by rain- 
fall ; but much more because of the constraint then exercised 
on drainage, whereby various river basins buried under the ice 
were forced to discharge their waters over passes into basins 
from which they are now well divided ; and also because of 
the temporary quality of glacial drainage, whereby streams 
flowed now here, now there, leaving on both lines the marks 
of their great activity. In many cases, active streams may have 
run over courses where no stream at all now flows. 
It follows from all this that the locus of washed deposits 
near the margin of the decaying and stagnant ice-sheet might 
often be independent of existing streams of the present time, 
as well as of pre-glacial streams ; and it is perhaps in this way 
that the apparently fortuitous distribution of glacial gravels is best 
accounted for. 
3 . MARGINAL WASHED GLACIAL DEPOSITS. 
Gravel and sand washed from the ice appear to have been 
formed sometimes on land, sometimes in standing water. On 
land the escaping streams would form an over wash of bedded 
gravels, on which the distributing and variable channels would 
frequently wander from place to place, building up a surface of 
gentle forward inclination at a profile of equilibrium. These de- 
posits would be broad if formed on a level country ; but would 
follow down the valleys in a country of strong relief. On the 
other hand, when the ice margin was fronted with standing water, 
the streams that entered it would build deltas, with lobate rim, 
steep plunging front beneath the water level, and nearly level 
upper surface slightly above water level and ascending gently 
to the point of chief supply at the edge of the ice. Deposits 
of these kinds are well known in Greenland and Alaska. Un- 
like the typical terminal moraine, the over-washed and delta 
PROCEEDINGS B. S. N. H. VOL. XXV. 31 SEPT. 189 ‘ 2 . 
