288 
GEOLOGY: W. H. BUCHER 
2. They trend in all directions, although a north-south trend is more 
common than an east-west trend. 
At first sight this seems to offer a serious objection to my interpreta- 
tion, since in open waters the direction of the current passes through 
all the points of the compass in the course of twelve hours, which would 
render the formation of permanent ripples impossible. The following 
observations, however, offer a clue to this problem. 
In 1881 Hunt^ visited the broad open gulf of Torbay on the south 
shore of Devonshire two weeks after a heavy storm. In Midbay, at 
a depth of over 12 meters, where the bottom usually is a soft muddy 
sand that clogs the dredge in a few minutes, he found the ground hard, 
producing "not a single shell or a particle of the usual muddy sand." 
Four weeks after the storm *'the ground was still very hard, both the 
dredge and a fishing-lead tied to a line humping along as though over 
ridges. Over six weeks after the gale the same spot had returned 
to its normal state. 
Similarly, Cornish^ found Pegwell Bay (Kent), in which ordinarily 
the tide never produces anything but small current ripples, covered 
with large tidal ripples after a heavy gale blowing into the bay. 
These observations indicate that the drift produced by periods of 
storms may so strengthen the tidal current as to produce large current 
ripples. This I suggest as the probable origin of our large Eden and 
Richmond ripples. 
The ripples observed by Hunt formed at a depth of over 12 meters 
with a tide of over 2 meters. In open waters the range of the tides and 
the velocity of the resulting currents would be much smaller than in the 
channel. With gales of similar strength, therefore, the same mechanical 
effect of the currents would be possible only at a much smaller depth of 
water. Allowing, however, for extreme conditions, we may safely say that 
it is probable that our Ordovician ripples formed in water less than 25 
meters deep rather than more. The Persian Gulf offers an interesting 
analogy. With an area of about 90,000 square miles, it has a mean 
depth of but 25 meters.^^ The tidal range along all its shores is 3 to 
3.75 meters.i^ 
The fact that at least three independent factors must combine for 
the production of these ripples, namely sufficiently strong tidal action, 
storms, and small depth of the water, explains why such large current 
ripples are not found in other seas, the sedimentary record of which 
is otherwise almost identical; e.g., certain parts of the Middle Triassic 
Muschelkalk of Western Europe. 
