THE CLYDE SERIES OF SOILS. 9 
cases the local country rock. This resulted in the formation of wave- 
cut terraces at the higher levels and in the deposition of sandy and 
gravelly beaches and bars concentrically around the margins of the 
lakes at different elevations corresponding to the different levels of 
the receding glacial lake waters. 
The materials formed in the deltas of both glacial and upland 
streams and the material deposited along the shore lines usually con- 
stitute the coarser grained sediments of glacial lake deposition. It 
is in such areas that large stone and coarse gravel are most frequently 
encountered, while only smaller gravel and the different grades of 
sand are found in the outwash plains and in those portions of the 
stream deltas which were carried farthest into the lake areas. Else- 
where the finer grained sediments, such as sandy loams, loams, and 
clays, prevail. 
In the smaller glacial lake areas, particularly where lake occupa- 
tion existed only for a brief period, the finer sediments dominate. 
In the case of all of the larger glacial lakes irregularities in the 
surface of the glacial till, accentuated in some instances by the exist- 
ence of local belts of moraine, gave rise to very unequal depth of 
water within the lake area. In the case of the glacial Lakes Saginaw 
and Maumee, curved moraines, concentric with the lake-shore line, 
rose above the lake level at some period of the lake stage. The waters 
of the lake acted against these moraines in the same manner as 
against the upland till, forming beaches and distributing the coarser 
and finer sediments along these shore lines and through the deeper 
lake waters. Other portions of the till and of water-laid moraines 
rose nearly to the surface of the lake and the crests of these sub- 
merged ridges were subjected to a degree of wave action only less 
than that along the shore lines. In certain areas the force of the 
water was only sufficient to move and redistribute the finer grained 
particles, while the larger gravel and the bowlders remained practi- 
cally in their former position, being somewhat accumulated at the 
surface through the removal of the finer earthy material. Where 
such action has taken place unquestioned glacial lake deposits some- 
times present the anomaly of abundant glacial bowlders and of large 
cobblestones. In seme instances it is even difficult to distinguish 
between glacial moraine or till and the feebly reworked glacial sedi- 
ments derived through the action of shallow lake waters across ridges 
which rose nearly to the surface of the lake. 
In other instances the drumlins and other glacial till ridges ex- 
tended above the surface of the lake waters and only their sloping- 
flanks and the lower lands between them were covered by glacial 
lake sediments. 
In every instance in the larger glacial lake basins the silt and 
clay derived from the different sources outlined were deposited in 
55812°— Bull. 141—14 2 
