8 BULLETIN 141, U. S. DEPARTMENT OF AGEICULTUEE. 
at the south maintained the first glacial-lake stages at altitudes as 
high as 1,100 feet in the Finger Lake region of central New York, 
while the later more extended glacial lakes in western New York 
occupied areas lying below 800 feet in elevation and thence declining 
to an altitude of 246 feet, the present elevation of the surface of Lake 
Ontario. At all of these elevations continuous or interrupted areas 
of lake sediments were deposited. 
The materials which were reworked and redeposited as glacial- 
lake sediments were everywhere of diverse origin. They were de- 
rived immediately from the heterogeneous mass of stone, gravel, sand, 
silt, and clay which formed the glacial till. This mass of earthy 
matter existed either upon or in the ice mass and was set free by 
melting or it had previously been laid down by the ice in the form 
of moraines and other deposits. In some localities it is possible that 
the glacial lake waters also derived some material from underlying 
consolidated rocks where these were not covered by glacial deposits. 
Such occurrences were of very small extent. 
In general, the largest amounts of material were contributed either 
by the glacial streams which flowed directly from the ice, by streams 
which flowed into the glacial lake basins from the uncovered but 
previously glaciated uplands, or through the direct action of waves 
and currents of the glacial lakes upon the till which formed the 
boundaries or the floor of the glacial lake basins. 
The streams which were formed directly from the melting of the 
ice carried glacial materials of all sizes, which were sorted and de- 
posited either in the form of long, low ridges chiefly consisting of 
gravel and sand, which are known as eskers, or as broad, low out- 
wash plains usually sandy in their general character. In both cases 
the finer sediments were carried to positions more remote from the 
ice front and were deposited in the deeper and quieter waters of the 
glacial lakes. 
Similarly the streams which flowed into the glacial-lake basins 
from the deglaciated uplands brought large amounts of material 
and this was partially or completely assorted to be deposited in the 
form of stream deltas near the outer margin of the lake areas. Fre- 
quently the coarser material was dropped in the form of low alluvial 
fans where the stream waters entered the lake. The finer materials 
from these sources were also carried to greater distances and de- 
posited with the finer sediments derived directly from the glacier. 
There was thus a mingling, in the majority of instances, of upland 
glacial till, of local country rock material, and of materials con- 
tributed directly through the melting of the glacial ice, all deposited 
to form the different grades of glacial lake sediments. 
Along the landward border of each of the larger lakes wave action 
played a considerable part in eroding both the glacial till and in some 
