18 GEOLOGY OF OHIO. 
The change of place of the delta was caused, however, for the most part, 
by oscillation of the sea level, and not, as Hllet supposed, by the simple 
filling of the channel with the materials transported by the river itself 
without change of bed. 
Prof. EK. W. Hilgard, in his interesting report to Gen. A. A. Humphreys 
on the Mississippi delta, states that he found true northern Drift 354 feet 
below the surface in Calcasieu district, Louisiana; and he cites evidence 
that, during the early part of the Drift period, the country about the 
mouth of the Mississippi was at least 600 feet higher than now. During 
the subsequent period of submergence it was, as he states, much lower 
than at present. It will be noticed that these facts accord precisely with 
those observed in the upper Mississippi valley and lake-basin, where, in 
the period of excavation of the buried channels, the country must have 
been high, and the drainage free. Afterward a great submergence oc- 
curred, which has left its indubitable records in the stratified Drift over- 
lying the Forest Bed and in the Loess. The locality where Prof. Hilgard 
found northern Drift in Louisiana was undoubtedly in, though not in the 
bottom of the old trough of the Mississippi, as I have noted elsewhere. 
T regard this as valley Drift, swept down the Mississippi from its northern 
watershed, when the continent was higher, and its current more rapid 
than now. 
On the west coast of North America evidence of a subsidence of the 
continent is afforded by the deeply excavated and partially silted-up 
channels of the Golden Gate, the straits of Carquinez, the trough of the 
lower Columbia, the Canal de Haro, Hood’s Canal, Puget Sound, and all 
the net-work of channels in that vicinity. As Dana first pointed out, 
years ago, the systems of inlets or fiords on both sides of our continent— 
channels which must have been excavated by suberial erosion—afford 
additional proof of modern continental subsidence. 
The importance of a knowledge of these old channels in the improve- 
ment of the navigation of our larger rivers is obvious, and it is possible 
that it would have led to the adoption of other means than a rock canal 
for passing the Louisville falls, had it been possessed by those concerned 
in the enterprise. 
I ventured to predict to General Warren that an old, filled-up channel 
would be found passing around the Mississippi rapids, and his examina- 
tions have confirmed the prophecy. I will venture still further, and 
predict the discovery of buried channels of communication between 
Lake Superior and Lake Michigan, probably somewhere near and east 
of the Grand Sable, at least between the Pictured Rocks and the St. 
