CONCLUSIONS. 61 
needles, beetle wings, etc. (Emerson, see ante, p. 10; Coleman, see ante, p. 11). 
It was noted by Emerson and Coleman that the vegetable material was almost 
always found in the coarse components of the banding. Streams draining 
wooded areas beyond the ice front washed the leaves and other material into 
the basin of deposition during the spring, summer, and fall months of stream flow. 
It is evident also that the wind must have blown leaves and other light material, 
such as spores and seeds, into the waters of the basin. Leaves and other material 
may also have fallen from the trees directly into the water along the margin 
of the basin. (Jeffrey, 1915, p. 218-230). In the winter the streams were 
frozen and an ice covering over the water of the basin prevented leaves and 
other vegetal materials from finding their way to the lake bottom. Occasional  - 
leaves and twigs might reach the basin during thaws in the winter, but most 
of the material would be deposited during the months of stream flow of spring, 
summer, and fall. This appears to be the most logical explanation of the 
presence of organic material in the clays. If the fine components of the band- 
ing were deposited in summer as well as winter, as many leaves and twigs would 
be found in them as in the coarse components. Coleman found wings of beetles 
in the Don River clays and these would appear to indicate summer deposition. 
Although Emerson and Coleman mention their findings in a brief description 
only, their significance in the argument for seasonal deposition is most important. 
How these leaves, twigs, spruce needles, and beetle wings in the silty layers of 
the clays can be explained, except on the seasonal theory, it is difficult to under- 
stand. 
In this paper the descriptions of the clays and slates have been given 
entirely from the standpoint of seasonal deposition. As far as the clays are 
concerned I feel convinced that the seasonal theory is in a very strong position 
and that the danger of its being abandoned is slight. When the Squantum 
slate is considered and the details of its structure compared with the banded 
clays, especially the Grantsburg clays of Pleistocene age described by Berkey, 
I feel very strongly that the origin of the banding in the slate is the same as in 
the clays. It is too soon, perhaps, to affirm finally that seasonal banding exists 
in the slate, although the similarities in the slate and clays are beyond question. 
Not only is the structure the same but the attendant phenomena plainly show 
the same origin. There are localities in the Boston region where this Cambridge 
slate formation outcrops, in which the regularity in the intervals of the banding 
is slight. In the Mystic quarries there is regular banding, irregular banding, 
and slate with no apparent banding. It is not certain, however, that this 
