The Thickness of Tee-Blocks. — Woodworth. 283 
In the case of adjacent ponds lying in the same general de- 
pression, examples of which are included in the above list, it 
is probable that the connecting furrow where wide and hav- 
ing kame-like sides, arose from the melting out of a narrow 
isthmus of ice connecting the larger masses; but where, as 
in so many cases, there is a well defined drainage line, begin- 
ning at the down-stream side of a large isolated pond, it 
seems highly probable that its existence depends upon an out- 
flowing stream and nothing else. We have to suppose then 
that in most of these ponds the ice even as late as the con- 
struction of the surrounding plains, rose high enough above 
the flanking gravels to furnish by its melting streams of con- 
siderable volume, though possibly of short duration. 
This conclusion is true, of course, only on the supposition 
that the melting took place on a land surface lying above the 
sea-level. Had the Cape Cod district, whence these exam- 
ples are taken, been submerged at the time I speak of, we 
should expect to find the marks of tidal fluctuations in the 
form of deltas or sand bars built backwards into the ponds 
from the old furrows, and these, too, in the hypothesis of sub- 
mergence, would have been largely shaped by the movements 
of the oceanic water. That the ponds and their furrows 
have not been subject to tidal invasion is proved by the 
absence of deltas in these situations. These ponds are then 
of themselves evidence of a subaerial origin of the adjacent 
stratified drift plains. 
When the ice-mass was buried or just escaped covering, 
having no sufficient elevation or mass above the general sur- 
face to create temporary streams, excurrent furrows would 
not arise. Even a considerable mass of ice might protrude 
above the sand-plain and yet fail to originate a surface drain- 
age system by reason of the ease with which large amounts 
of water may percolate through these porous deposits. 
Prof. G. F. Wright, in his book on "The Ice Age in North 
America," gives an illustration of an ice-mass "'one hundred 
or more feet thick" seen by him about half a mile in front of 
the Muir glacier, in the process of melting and with its sides- 
encumbered with gravels. To this ice-mass he ascribes the 
origin of kames with an encircled kettle-hole. From his de- 
scription and the reproduced photograph, I am led to suppose 
