GEOLOGY: W. H. BUCHER 
287 
grain, as conglomeratic sands (Blackhand formation) or fragmental 
limestones, never on fine-grained sediments, e.g., on dense blue argil- 
laceous limestones. These are, however, frequently covered with small 
current-ripples, ranging in wave-length from 1 to 30 cm., and are often 
interstratified with fragmental limestones of coarse grain covered with 
large ripples and separated from them only by thin layers of shale. 
The calcareous layers show dehcate tracks of gastropods or trilobites 
well preserved which practically exclude any current action. 
This seems to indicate that the current in question varied in intensity 
from a maximum to nil, in relatively short intervals. The finer sedi- 
ments could record only the weaker movements, as stronger currents 
would have thrown them into suspension. 
5. In the Ordovician, I have repeatedly found large asymmetrical 
ripples on two successive limestones, not more than a foot apart, with 
nearly the same strike, but with their lee sides facing in opposite direc- 
tions. The current, therefore, reversed its direction in relatively short 
intervals. 
Observations 4 and 5 exclude ocean currents of larger dimensions, 
while they point consistently to tidal currents. These, too, are the 
only marine currents, flowing parallel to the shore-line, in which veloci- 
ties of at least 1 m/sec, which seem necessary to produce the effects 
observed, are found over large areas. 
In 1901 Cornish^ described from the English Coast large current- 
ripples corresponding closely to those observed in the fossil state. On 
open shores, such as at Mundsley (Norfolk, p. 183), above the mouth 
of Barmouth Estuary (p. 173), or especially on the Goodwin Sands 
(p. 189), about six miles off the shore of Kent, these tidal ripples in- 
variably trend at right angles to the shore, often at right angles to the 
waves. On the open shore, too, their wave-length is the same as that 
of most large Paleozoic ripples, while those observed in estuaries, where 
the velocity of the tidal current is greatly increased, have a greater 
wave-length. 
I therefore infer that the large current-ripples described were pro- 
duced by tidal currents. Those of the Brassfield formation in Ken- 
tucky offer a direct analogy to those of the Enghsh Coast. 
The ripples of the Lorraine and Richmond Formations, however, 
offer an additional problem. 
1 . They are not limited to a relatively narrow zone in the neighbor- 
hood of the shore, but formed (probably more or less synchronously) 
throughout the area of the Cincinnati Antichne, that is, over an area 
of at least 15,000 square miles and probably much more. 
