PLATE 16, 
Figure 1— PHoromicrocrarH or SquantuM TILLITE. 
The following minerals have been found in the tillite:—quartz, feldspar, sericite, epidote, melaphyre, 
chlorite, limonite, quartzite, and calcite. The angular rock particles of the matrix vary in size from 
coarse sand down to those with a diameter of 1/1000 mm. or less. 
Figure 2.— PuoromicrocRaPH oF BanpEp Starr, Squanrum Hap. 
This shows a typical specimen of the banding above the tillite at Squantum Head. These layers 
were chosen go that the complete cycle could be easily shown in one view. The magnification here is 
ten diameters. It will be noted that the layer of fine material is on the whole, homogeneous in its nature. 
The transition from coarse to fine upward is usually gradual, as in Figure 3, Plate 16. The transition 
from fine to coarse is usually abrupt, and the finest material of the fine layer is on top. This finest 
material on top is often beautifully rippled by extremely gentle current action. It sometimes happens 
that this finest material on the fine layer is absent. In such cases it is most likely that the succeeding 
currents of the active water phase of the cycle have removed it. In the layer of the active water phase 
tiny lenses of very fine material may be seen. From a study of many slides in which continuous threads 
of such fine material are present, it is inferred that these lenses are merely remnants of such fine layers. 
Figure 3.— PHOTOMICROGRAPH OF COARSE LAYER. 
This is a view of the coarse layer seen in Figure 2. It was taken near the top of the coarse layer and 
shows the transition between the coarse and the fine layers. The magnification here is about twenty 
diameters. Note how gradual the transition is compared with the abrupt change from fine to coarse. 
Note also the disturbed nature of the material as compared with the undisturbed nature of the fine. 
Figure 4— PHOTOMICROGRAPH OF FINE AND COARSE LAYERS. 
This shows the fine and coarse of another specimen. Only part of each layer shows. The magnifi- 
cation is about ten diameters as in No. 2. Note the fine sediment at the top of the fine layer. Very 
gentle ripple-marks may be seen along this horizon. The coarse layer shows extremely thin laminae 
with very regular intervals. These differences suggest day and night changes, but at present it is only 
possible to state that there is a difference between glacial streams at night and during the day, and if 
the conditions of deposition were just right for their registration, such differences in sedimentation 
should be registered and, at least partially, preserved. 
