282 
The American Geologist. 
May, 1901. 
advanced to the westward upon the underl} ing one, giving a 
crest plane inchnation for the series of about 45° east. 
The striking feature of the bed w^as a band of highly mi- 
caceous sands forming the frontal slopes of the entire series 
of crests in the bed as shown in the annexed figure, by the 
shading. 
FIG. I. CROSS-SECTION OF A PORTION OF THE LAKE WALDEN GLACIAL SAND 
BED, SHOWING A CURRENT MARK WITH MICACEOUS BANDS IN THE 
FRONTAL SLOPES OF THE CRESTS. 
The micaceous bands were about half an inch in width. 
They dipped 45° east, as stated above, parallel to planes pass- 
ing through the respective crests. The individual particles of 
mica lay parallel to the crest slope, producing an obvious 
false bedding totally distinct from the straticulate structure of 
normal cross-bedding in relatively homogeneous sands. The 
micaceous bands were between four and five inches apart. 
The type of rippled stratification with which the micaceous 
banding was associated shows that the banding developed un- 
der the action of the vortical movements of the bottom drift of 
a slowly moving current. In analogy with the observed vor- 
tices of a continuous bottom current, my colleague, Dr. Jaggar, 
suggests the whirling movement of the water must have been 
as in the annexed figure at the crest of each current mark. ( See 
fig. 2. ) In the dead space on the frontal slope, particles of 
mica which were caught in the bottom movements would come 
to rest as the deposit grew upward. 
FIG. 2. SCHEME OF VORTICAL MOVEMENTS ABOUT THE CREST OF A CURRENT 
MARK. THE SHADED SLOPE SHOWS THE AREA ON WHICH THE PART- 
ICLES OF MICA HAVE COME TO REST BENEATH THE NODE JUST IN AD- 
VANCE OF THE CREST. (AFTER SKETCH BY J.\GGAR.) 
In this connection, it will be recalled that Spurr in this 
Journal (vol. xiii, 1894, pp. 43-47. 201-206, with discussion by 
Jaggar. pp. 199-201), described a rhythmic succession in tex- 
