46 
The American Geologist. 
January, 1894 
cumulate many large pebbles, finer gravel and loose sand; B, 
the forward part of the gently sloping side of the ridge, 
which mainly receives the pressure of the current and accu- 
mulates a layer of firmly packed sand; and C, the upper part 
of the steep side, where coarse fragments, on account of their 
weight, do not lodge, and where the force of the current is 
little felt. This last forms the layers of loose sand. There is 
often a fourth division, lying between A and B. This posi- 
tion receives but sparingly the coarser fragments; and it is 
somewhat protected from the force of the current. The re- 
sult is 7>, a layer of loose sand and fine gravel, nearly like C. 
Fig. 'I.— A. Coarse gravel. B. Compact sand. C. Loose sand. I). Loose sand with 
some gravel. Scale, one incli to a foot. 
The analysis of this structure gives some clue to the con- 
ditions under which the deposit was laid down. It was in 
shallow water, and the current was approximately constant, 
both in its velocity, as is shown by the considerable extent 
of these false layers of coarse material (for if the velocity 
should change the material would also change, and so destroy 
the semblance of a layer), and in its direction (from the 
north), as is shown by the regular and unvarying form of the 
ripple-marks. The velocity may be estimated from the size 
of the pebbles in the coarse layers. The stream was able to 
move these along on the gently inclined slopes, but was un- 
able to do so when they were in a place where the force of 
the current was slightly warded off. Thus the size of the 
larger fragments marks the limit of thecarrying power of the 
water. 
The average size of these larger fragments may be estimated 
as between two and two and a half inches in diameter. Acord- 
