196 SURFACE GEOLOGY. 
. one hundred feet above the rock bottom of its excavated 
trough. The Chagrin, Vermilion, and other streams running 
into Lake Erie exhibit the same phenomena, and prove that 
the surface level of the lake must have once been at least 
one hundred feet lower than now. 
The bottom of the excavated channel in which Onondaga 
Lake is situated, and the Salina salt-wells bored, is at least 
four hundred and fourteen feet below the surface level of the 
lake and fifty feet below the sea level. (Geddes, Trans. 
New York State Agricultural Society, 1859.) 
The old channel of the Genesee River at Portage, de- 
scribed by Professor Hall in the Geology of the Fourth Dis- 
trict of New York; the trough of the Hudson, traceable on 
the sea bottom nearly one hundred miles from the present 
river mouth; the deeply buried bed of the Lower Missis- 
sippi, are additional examples of the same kind; while the 
depth to which the Golden Gate, the Straits of Carquinez, 
the channel of the lower Columbia, the Canal de Haro, 
Hood’s Canal, Puget Sound, etc., have been excavated, indi- 
cates a similar (perhaps simultaneous) cloyution and erosion 
of the Western coast of America. 
The falls of the Ohio— formed by a rocky barrier across 
the stream — though at first sight seeming to disprove the 
theory of a deep continuous channel in our Western rivers, 
really afford no argument against it, for here, as in many 
other instances, the present river does not follow accurately 
the line of the old channel below, but runs along one or the 
other side of it.- In the case of the Louisville falls the Ohio 
runs across a rocky point which projects into the old valley 
from the north side, while the deep channel passes under the 
lowland on the south side, on part of which the city of 
Louisville is built. 
The importance of a knowledge of these old channels in 
the improvement of the navigation of our larger rivers is ob- 
vious, and it is possible it would have led to the adoption of 
other means than a rock canal for passing the Louisville 
