42 
MUSEUM BULLETIN NO. 25. 
which extended continuously over the bottom from a depth of 
1 foot near shore to 19 feet about one-third of a mile from 
shore. They were seen very clearly to a depth of 15 feet, and 
less distinctly to 19 feet and beyond that depth vision failed. 
A sounding lead drawn over the bottom showed clearly by the 
jerking pull on the line that the ripple-marks continued out into 
water about 24 feet deep. Beyond this depth the increased depth 
of water takes up or modifies the vibration on the line to such an 
extent as to cause this method to give no precise information 
regarding ripple-mark. Attempts to secure plaster moulds of 
ripple-mark in 30 feet of water failed, apparently because of the 
strong bottom current which undercut the edges of the apparatus 
before the plaster had hardened. The greatest depth at which I 
have taken moulds of ripple-mark is 27 feet. 
In considering the maximum depth at which ripple-mark 
may occur it is important to discuss separately the two kinds of 
subaqueous ripple-marks which have been described. The 
symmetrical type of ripple-mark produced by wave action will 
certainly be developed on sandy beds at any depth to which the 
effective oscillatory movement of waves extends. I have shown 
elsewhere 1 that wave action of an extremely vigorous type extends 
to depths of 10 fathoms in lake Ontario. Wave action which is 
violent enough to break up a lake tug at a depth of 10 fathoms 
could hardly fail to make itself felt on the bottom at several times 
that depth. Fifty fathoms would seem to be a conservative 
estimate of the depth at which ordinary storm waves would 
develop ripple-marks on the bottom. With reference to this 
question Dana stated that: 2 “Ripple may form over the bottom 
as far down as the oscillation in the water extends, which may be 
a hundred yards or more.” 
In the case of asymmetrical ripple-mark the only factors 
essential to their formation are current action and suitable 
bottom material. There is no reason w*hy both of these may not 
be found at any depth known in epicontinental waters. Unlike 
wave action current action may extend to any depth. Current 
ripple-marks may, therefore, be formed at great depths. 
1 Sedimentation in lake Ontario, MS. 
1 J. D. Dana, Manual of ecology, 4th. ed. f 1895, p. 94. 
