50 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
ponent and might indicate such high winds, as are common today, at the begin- 
ning of pronounced cyclonic and anticyclonic atmospheric control in the fall. 
The fairly regular occurrence of these coarse layers would indicate a regularly 
recurring cause. Seasonal changes of temperature or periods of high wind, 
therefore, would explain regular recurrences of phenomena such as have been 
described better than anything which has suggested itself. 
The sediment in the finest glacial clays is, on the whole, finer than in the 
glacial slate at Squantum, although as fine sediment may be found in the slate 
as in the clays. This would seem to indicate that this particular slate was 
deposited in water with a slightly greater movement than in the case of the 
clays. The sediment in the slate is of about the same texture as that found 
in the seasonal banding at North Bath and Lisbon in the Ammonoosue Valley, 
already: described (p. 24; also Plate 3). Some banded slate taken from the 
subway excavation at Harvard Square has as fine a texture as the Woodsville 
clay and the banding is as regular as any seen in the glacial clays. Almost 
all the slate of the Cambridge formation found in Cambridge and Somerville 
is of very fine texture, the grains averaging about 1/1000 mm. with some 1/1200 
mm. This would indicate that the water was deeper there than at Squantum. 
The sublacustrine origin of some of the tillite recently found by Woodworth in 
Watertown, would also indicate deeper water than that at Squantum. (Upham, 
1896, p. 371-375). : 
In the clay-pit of E. M. Lamarre at Woodsville, already described (p. 18) 
there are contorted zones between undisturbed layers in the clays. At Squan- 
tum similar contorted zones may be seen. Mr. Lahee called my attention to 
these several years ago. (See Lahee, 1914, p. 786-790). In Figure 1, no. 2, I 
have sketched the mode of occurrence of these folded and crushed layers. If 
this figure is compared with Figure 1, no. 1, the similarities of the two sections 
will be apparent at once. First of all, it should be noted that the contorted 
zones in the Woodsville clays are, on the whole, thicker than at Squantum. At 
Squantum the water was probably not as deep as at Woodsville, and could not - 
float as large icebergs as could be floated at Woodsville. This inference is 
favored by the fact that the sediment at Woodsville is somewhat finer than at 
Squantum. It should also be noted that the contorted zones grow thinner up- 
ward, indicating possibly a retreating ice front, and hence, on account of melt- 
ing, smaller and smaller bergs at this spot. 
Pebbles are frequently found embedded in the contorted layers. The 
finding of such pebbles in the contortions of the glacial clays and in these similar 
