106 NEW YORK STATE MUSEUM 
few miles south of Boonville, along this stream, was mostly cut by 
the fairly large stream which drained the glacial lake at this stage. 
The southward discharge through this channel appears to have 
been into the Lansing Kill lake where a delta deposit was formed 
a few miles north of Rome and now the site of the Delta reservoir. 
Lansing Kill lake in turn drained through the Mohawk Valley. 
Still further retreat of the ice lobe allowed Black lake to ex- 
pand greatly until it reached from the region around Forestport 
to north of Lowville, when it had a width of from five to ten miles. 
When the ice withdrew enough to permit a discharge of water 
around the north base of Tug hill, and into Lake Iroquois, the level 
of the lake rapidly fell until the ice barrier was completely removed. 
The former presence of this great glacial lake is conclusively shown 
by the extensive development of unquestioned delta deposits. 
Where the streams from the Adirondacks, especially the larger 
ones such as Black, Moose, and Independent rivers, emptied into 
the lake, delta deposits were rapidly built up to near the lake sur- 
face because those streams were heavily charged with debris from 
the newly drift-strewn mountains. These delta deposits became 
more or less merged, and they show a remarkable concordance of 
altitudes over the sand flat or sand plain country on the east side of 
Black river. This great delta deposit is several miles wide; very 
flat-topped except where trenched by postglacial streams; presents 
a steep front toward the river; and shows a depth of from 200 to 
250 feet along the western edge. Figure 35 clearly shows the rela- 
tion of the delta deposit to the old rocks of the valley. 
Racecas (12) 7renton limestone 
Oswego sandstone Femelia-Lowville simestone 
Lorraine shale & sandstone = J 2oze1e strata (concealed) 
E:=] Utica shale Precambric rocks 
Fic. 35 East-west section across the Black river valley, 2% miles north 
of Lyons Falls, showing the terraced character of the Paleozoic strata and 
their relations to the Precambric Adirondack rocks. On the east side, the 
position of the glacial lake delta deposit is shown. Length of section 12% 
miles. Vertical scale greatly exaggerated. 
After W. J. Miller, N. Y. State Mus. Bul. 135 
