Glacial Features of Long Island. — Bryson. 391 
visit it was gratifying to find this conjecture confirmed. It 
also proves, I think, what I have always maintained, that ket- 
tle-holes are really subglacial valleys ; for lake Ronkonkoma 
is only an enlarged kettle-hole. 
If the reader will examine a map of Long Island, it will be 
seen that there is quite a stream draining into Smithtovvn ba} T 
from the region of Ronkonkoma. It forms one of the largest 
indentations on the north side of the island, and if this de- 
pression is followed up it will be found connecting with the 
lake in question. During the glacial floods the water must 
have flowed southward through it into the ocean. The largest 
channel enters the lake on the north, and consists now of a 
marshy depression. This doubtless formed at one time the 
main inlet. There are other smaller depressions, or old chan- 
nels, entering the lake on both sides, and where the old 
streams met the lake is the widest. 
The depression at the south end was probably the main out- 
let, although there is little drainage, if any, through it at 
present; but the old channel, or channels, can still be traced 
through the terminal moraine and southern plain to the Great 
South bay. The bottom of the lake is several feet below the 
present level of the sea (I have not the exact figures at hand),* 
and the theory of oscillation has been brought into requisi- 
tion to account for certain phenomena that cannot very well 
be explained on any other hypothesis, at present; yet there 
are serious difficulties in the way, even with this interpreta- 
tion. Prof. James D. Dana thinks that the island must have 
stood about J00 feet higher while the ice cap lay over it. and 
that it sank again to its present level when relieved of its 
burden. There are no signs of such changes having taken 
place, if we may judge by the contour of the island, as the 
old water channels are united in such a way as to preclude 
the idea of oscillation, and yet-there are certain phenomena 
that seem inexplicable without it. That is, it seems as if the 
land must have been higher or the sea lower during the gla- 
*[Prom Mr. Upham's description of the terminal moraine forming 
tin- "backbone" of Long Island, we are able to supplj these figures: 
"Lake Ronkonkoma, the largesl bodj of fresh water on the island, lies 
exactly in the course of ihis siM-irs of hills. [ts area is stated in lie 
about 160 acres; its hight, fifty-four feet above sea: and its extreme 
depth, eighty-three feet." (Am. Jour. Sci., 111. voh win. p. 85, Aug., 
1879.)— Eds.] 
