Correspondence. 279 
the same, although not so determinable in places. It is very light on the 
Shinecock hills, for here the stratified gravel comes very near the surface. 
The bottom drift is also variable, and subject to many modifications. 
The Rockaway Beach railroad, that cuts through the ridge north of 
Woodhaven, exposes an interesting section of drift. The moraine is 
broken up by old subglacial streams, and adjacent to these depressions, 
the material near the edges of the bank, show signs of stratification, but 
these stratified layers never extend clear across the cut except near the 
surface. In the center of the bottom part of the drift is a mass of 
boulders in a sandy matrix, and over this is the hardpan, which is also 
fullof erratics. Then comes the modified drift, and over all the so-called 
-englacial drift which probably was laid down after the floods had sub- 
sided. The modification of the drift at this point tends to prove, I think, 
that kettle-holes were in some way connected with subglacial rivers. 
North of the terminal moraine the whole bottom part of the drift 
seems to be modified, although a small section was exposed at Ridge- 
wood, where underneath some fifteen or twenty feet of stratified sand 
and gravel was a stratum of unmodified boulder clay of unknown 
depth, and there may be other sections like it that have not been ex- 
posed. Ridgewood, near Brooklyn, is situated near an old water chan- 
nel that comes up through the Newtown creek depression. The under 
boulder drift was probably deposited when the ice-sheet lay over the 
island. The stratified sand and gravel tell the story of the floods dur- 
ing the melting of the glacier, and the upper deposit or englacial drift 
was laid down when the ice-sheet retreated. This upper drift thins out 
towards the depression showing that the floods must have prevailed 
while the deposition was going on. The waters must have receded, how- 
ever, before the ice-sheet had disappeared, for the depression as well as 
the ridges are covered with unmodified boulder drift. 
Professor Agassiz said: “All American drift is bottom drift.” And in 
a sensethis is true. I am inclined to think that the so-called subglacial 
drift is as much englacial as the surface portion of unmodified till, that 
is, both were held 77 the ice-sheet until deposited. 
On Long Island as the glacier advanced from the main land the sub- 
glacial streams advanced with it, modifying the drift and carrying much 
of the detritus beyond the southern limit of the ice-sheet. The south 
side of the island is chiefly composed of this stratified material. These 
ancient streams can be traced by the depressions from the sound to the 
sea, and the upper deposit of unmodified drift that covers in general, 
the stratified deposits, shows, I think, that the streams were subglacial 
and not superficial. There is little direct evidence on Long Island of 
superglacial drift. The subglacial beds of stratified gravel are not so 
s‘anty as Mr. Upham supposes, for, as far as my observations go, they far 
exceed all other glacial deposits. The greater part of the terminal moraine,. 
moraines of recession, or kame moraines, and the bottom part of the 
valleys and plains owe their modified condition to subglacial currents. 
I am aware that the terminal moraine is generally spoken of as being 
composed of unmodified drift. This is true. of the surface part only, 
