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CRITERIA FOR AQUEO-GLACIAL SEDIMENTATION. 33 
The phenomenon noted above was repeated as already described, except that the process 
was slightly more rapid than in the first case.” Kinpix, 1916, p. 543. 
It is evident that in fresh-water streams and lakes much sediment may be 
transported for many miles before settling. The coarser grains of the clay, 
might settle rapidly, but much of the finer material would remain in suspension 
for months and might not all settle, even in quiet water under ice, during a 
long winter. 
By a study of the sedimentation it should be possible to determine whether 
marine or fresh-water conditions prevailed at the ice front, or in the area of 
deposition beyond the ice. If the glacial sediment was transported into salt 
water it would be logical to expect relatively thick deposits. Tidal scour, how- 
ever, would probably erase anything like a regular order of deposition, except 
perhaps in water deep enough to be out of reach of such action. In fresh-water 
deposition it is evident that the thickness of seasonal deposits will depend largely 
on the amount of sediment supplied to an area of deposition, and also on the size 
and shape of the area of deposition. If the glacial waters could not travel far 
the deposits should be thicker than in a large body of water, where they could 
spread or be transported for many miles. Lake Louise in the Canadian Rockies 
illustrates the former case, and the Lake of Geneva in Switzerland might be given 
as an example of the latter. The size of the glacier will also influence the thick- 
ness of the seasonal deposits, for as already noted, other things being equal, 
glacial streams will always be larger from a large glacier than from a small one. 
In the retreat of the Wisconsin ice sheet the streams should certainly have been 
large. Needless to say, the temperatures would also have a most important 
bearing on the glacial torrents. 
B. In considering the ratio between the widths of the coarse and fine 
components of the banding, a factor must be noted which may have an import- 
ant bearing on this ratio. All tills vary somewhat in the amounts of coarse 
and fine sediments in their matrices. Tills with the finest materials are usually 
found in lowland or valley regions. On the uplands the matrix of till usually 
has a greater percentage of coarse material. (Emerson, 1917, p. 137). The 
matrix of till is sometimes almost altogether sand with very little rock-flour 
or clay. As most of the banded clays have their origin under glaciers, as the 
result of grinding, it would be natural to expect the ratio of the thicknesses 
of the coarse and fine components of the banding to be determined to some 
degree by the ratio between the coarse and fine sediment in the till. As the 
material of the glacial clays usually comes largely from the till of lowland or 
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