38 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
deformed zone. The folding observed might result from the downward pres- 
sure of the ice alone, or by the dragging effects of moving ice. Inasmuch as 
the directions of the folds correspond in nearly every case observed in the Con- 
necticut River clays to the direction of ice movement, I have considered it more 
probable that the results noted were due to ice drag than to vertical pressure 
alone. 
It is also possible that the deformed layers in question might be the result 
of creep toward an unsupported edge, due to the weight of superincumbent 
clays alone. 
Where glaciated rock-fragments are found mixed with or lying on the con- 
torted zone, as noted above, I believe it is good evidence of deformation by 
contact of the ice itself, whether by icebergs or by a moving glacier. In most 
cases the magnitude of the deformation, together with the nature of the strata 
above the contorted zone, would decide which of the two kinds of ice action 
produced the results. Icebergs would deform the clays and pass on, without 
affecting the general sedimentation. If a moving glacier did the work, it is 
likely, although not necessary, that the strata just above the contortions would 
differ in thickness and texture from the layers of the contortions and those 
just below them. 
In cases of deformation where there is no good proof of direct ice action, 
-such as glaciated rock-fragments or till, it is often difficult or impossible to decide 
what caused the movements of the layers. The direction of movement of the 
deforming force, whatever that might have been, may eliminate one or more of 
the agents or methods under consideration. 
B. At rare intervals a layer of rock-flour, from an inch to three or four 
inches thick, may be found. The true explanation of such layers is not clear. 
The diversion to one side of the glacial stream which supplies the material, 
caused by the temporary blockade of the usual channel or course by a large 
stranded berg, might, for a short time, transport to the locality in question 
much more of the rock-flour type of sediment than usual. Upon the melting 
of the berg and its consequent floating away the water would once more resume 
its normal course. Thin layers of gravel are sometimes, but rarely, met with 
in the midst of regular banding in the finest clays. The evident sorting of 
the pebbles appears to indicate temporary increased stream action also as the 
cause in such cases, as in the cases of rock-flour layers. 
Another possible explanation for these abnormal layers of silt and gravel 
or sand in the midst of the regular banding of finest material, might be the 
