RECENT AND FOSSIL RIPPLE-MARK. 
41 
to those quoted we have not cited them in the absence of their 
confirmation by further observations.” 
In recognizing the importance of these observations it is 
necessary to point out that Siau fails to consider the possibility 
that the ripple-marks which he found at such great depths may 
have been caused by tidal currents. While this possibility does 
not seem very probable to the writer it must nevertheless be taken 
into account and until eliminated the parallel zones or ridges 
found by Siau at 578 feet cannot be considered conclusive evi- 
dence of wave action at that depth. 
Rather sharply contrasted with Siau’s statement that he 
observed ripple-mark with crests 11 to 20 inches apart is 
Pirsson and Schuchert’s 1 report of Prof. Verrill’s observation near 
the island of Anticosti. “Ripple- marks have been seen and 
measured in depths of 75 feet with the ridges still 3 inches 
apart.” It is possible that the discrepancy between the two 
statements with reference to amplitude at a considerable depth 
may be due to the greater amplitude being the product of wave 
action and the lesser the result of tidal current action. It is 
not stated how the ripple-mark was “seen and measured” at the 
considerable depth of 75 feet. 
The statements of some geologists who have had oppor- 
tunities for examining the. sea bottom through the clear sea water 
and brilliant light which prevails on sub-tropical coasts indicate 
that under these favourable conditions ripple-marks may be 
seen from the surface at considerable depths. Prof. John L. 
Rich 2 states that, “I have seen from a glass-bottomed boat 
ripple-marks developing in water estimated to be 70 or 80 feet 
deep, at Avalon, California, under the influence of the ocean 
swell. At Avalon in the deeper water the ripple-marks might 
be likened more nearly to windrows than to anything we are 
likely to think of as ripple-marks. They must have been 5 or 
6 feet apart and 1 or 2 feet in height.” 
The only observations of my own bearing on this question 
were made in lake Ontario. In the bay at Wellington on lake 
Ontario, I was able one still, bright day to observe ripple-marks 
1 Pirsson and Schuchert, “A text book of geology," 1915, p. 491. 
* Letter to the author, Feb. 15, 1915. 
