CONCLUSIONS. 59 
7. CONCLUSIONS 
In view of the fact that some geologists doubt the seasonal nature of the 
banding in the glacial clays, it may be well to examine the evidence for the 
seasonal theory before passing judgment on the seasonal origin of parts of the 
glacial slate at Squantum, and the same slate in other parts of the Boston basin. 
De Geer found that each pair of coarse and fine components of the banding 
was connected with a small annual moraine. These moraines were from 200 
to 300 meters apart. The geologists who were with de Geer when he exhibited 
and explained his evidence in the field, during the International Geological 
Congress at Stockholm in 1910, saw for themselves that he was justified in 
his contentions. (See p. 6). 
To rule out those agencies which cannot produce banding of the nature 
found in the glacial clays, may help to clear the way for any cause capable 
of producing the regular alternations of coarse and fine sediment found. The 
main factors which can produce differential aqueo-glacial sedimentation are:— 
the swinging of a stream across a delta; the difference of day and night melting 
of glaciers; more or less regular cyclonic and anticyclonic conditions during 
part of the year, with or without rain or high winds; periodic or seasonal winds 
capable of transporting sediment; tides; and the alternating conditions of 
summer and winter. 
As has already been noted, a stream swinging across a delta may deposit 
alternating, irregular, and discontinuous layers of coarse and fine sediment. 
These are not to be confounded with the alternating layers in deeper water in 
front of deltas, believed to be of seasonal origin. 
If the regular alternations of coarse and fine sediment of the deeper waters 
are due to day and night stream flow from the glaciers, what caused the minute 
but well-defined alternations in the coarse components of the banding as made 
out by Berkey in the Grantsburg clays? These layers as described by Berkey 
give every evidence of deposition by moving water, with periods of quiet 
water intervening. The structure of this minute banding did not suggest to 
Berkey gentle wave action on the bottom. It would be impossible for the 
amounts of fine clay found in the average fine components of the banding to 
settle in twelve hours. It is much more reasonable to believe that these minute 
laminae in the coarse components mean day and night effects than to ascribe 
this cause to the larger units of the banding. Berkey gives the best account 
