10 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
5,000 years for the ice to retreat from its most southern limit in Germany to 
southern Scania. This would make a total of 17,000 years for the whole retreat 
of the great Scandinavian glacier of the last Glacial epoch from its greatest 
extension to the present mountain limits, plus the time which has elapsed since 
the ice reached its relatively stationary condition of today. 
Many years after Hitchcock recorded his observations, Emerson, 1887, 
his successor, made a study of these same banded glacial clays in the Connecti- 
cut Valley and came to the following conclusions: 
“Tn all its deeper waters the flat, laminated clays were being deposited, while the sands 
of the deltas were extending out from the shore. Each layer of the clay, on an average of 
two-fifths of an inch thick, represents a year’s deposit. The clays are, at the Northampton 
bridge, above 120 feet thick, and at East Street bridge above fifty feet, which would give 
numbers for the duration of the lake favoring the idea that the Glacial period was not more 
than 10,000 years ago, one of the shortest estimates. In these clays I have found an abundant 
glacial flora, proving that the lake succeeded immediately to the ice, and I have found indi- 
cations of several re-advances of the ice ploughing up the sands of the lake.” Emrrson, 
1887, p. 404, 405. 
In 1898, Emerson, explaining the laminated clays near Northampton, writes: 
“While the “fat” portions of the clay layers are very uniform in thickness and grain, 
the variation in the thickness of the layers depends upon a thickening or thinning of the sandy 
portions of these layers, which may or may not be accompanied by a corresponding change 
in the grain of the latter. At times the fat lamin separate and take in between them 12 
to 16 inches of a sand but little coarser than that of the coarse portion of the layers at the 
Hadley locality, as is the case in a large portion of the Wapping cutting. At other times the 
‘grain increases to medium or coarse. . 
“The fat lamine seem to be purely a sediment of matter held in suspension when there 
was scarcely a trace of current, the lean lamine to contain in gradually increasing proportion 
the fine material carried over the bottom by the friction of a slow current, which was regularly 
intensified for the formation of the thin films of sand which separate the layers. One finds 
these clays as regular as a pile of thin deals over all the basin, and I imagine that each layer 
represents a year’s work of the flooded river. The fat layers were thrown down in the winter 
impartially over every portion of the lake bottom, and with the breaking up of the ice in 
spring the flood swept it off those portions where it had strong current, at times just crumpling 
it, as shown in figs. 39 and 40, p. 647, but over the deep lake bottom only rippling its surface, 
the fat tenacious clay resisting erosion slightly, while the coarse material brought in by the 
tributaries was pushed in sheets out over the delta flats and dumped over their fronts, and in 
small quantity carried out over the clays. In exceptional floods thin films of these sands 
were carried down across the very middle of the lake, as at the Hadley locality, and came 
at the beginning of the spring, for the coarse sand rests directly in rippled hollows of the 
surface of the finest clay. In this sand are found the twigs and reeds and leaves brought 
down by the tributaries, and the sands grade upward into the lean portion of the layer, which 
represents the uniform high water of the glacial river during the summer and which is a true 
“gletchermilch”’ and this in its turn grades upward into the fat deposits produced by the 
clarifying of the waters during the succeeding winter. This would conspire with the fact 
