290 
GEOLOGY: W. H. BUCHER 
channel and on the banks of Newfoundland^^ a considerable thickness 
of sediment must be stirred up. The heavier particles, shells and skele- 
tons, however, are concentrated on the bottom, drifting with the cur- 
rent and eventually thrown into large current ripples. The relatively 
short duration of this current action explains observation 7. The sus- 
pended clay settled later, forming the layer of shale overlying the rip- 
pled limestone layers (observation 6). Since the thickness of sediment 
which could be thrown into suspension during such storm periods is 
limited, the thickness of the resulting fragmental limestone is limited, 
while shale on shale could accumulate indefinitely as long as no abun- 
dant animal population settled on it (observation 3) . The rippled layers 
were preserved if sufiicient shale was added between two exceptional 
storm periods to prevent the stirring of the sediment from reaching 
down to it. A decrease of the clay supply, however, would reduce the 
rate of sedimentation and allow ordinary storm waves to expose the 
fragmental layer, which, under the action of the shifting normal tidal 
current, would suffer a surficial redistribution of material, resulting 
in complete leveling of the surface. A sufiicient rate of sedimentation 
must, therefore, be considered as a fourth factor determining the forma- 
tion of large current ripples (observation 8). 
From the above it follows that the rough rhythm of sedimentation, 
shown by the recurrence of fragmental limestones between shales and 
argillaceous limestones, is due to the interference of two, probably not 
strictly periodic processes : the shifting of the centers of animal popula- 
tion on the sea bottom and the occurrence of storm periods of excep- 
tional violence. 
If the interpretation presented above is correct, the geographic con 
ditions indicated by the large current ripples of the Upper Ordovician 
of the Cincinnati Anticline may be summarized as follows: 
1. A sea having sufficient connection with the open ocean to allow 
relatively high tides. 
2. Sufiicient area to permit the formation of strong winddrifts in 
most directions during periods of storms. 
3. A depth small enough to admit of a strong action on the bottom 
sediments by winddrift and tidal current combined, probably 25 meters 
or less on the average. 
4. Atmospheric conditions providing for the occurrence of storms, 
blowing from all points of the compass, such as tropical cyclones or 
those of intermediate latitudes. 
iLinney, W. M., Rep. Geol. Garrard Co., 1882, (16); Washington Co., 1882, (10-11); Lin- 
coln Co., 1882, (13); Mason Co., 1885, (8); Bath and Fleming Cos., 1886, (10, 62-69); Shelby 
