1887.] 21 (Haupt. 
nel produced by the ebb. Between these limits are found one 
or more secondary or swash channels, which provide egress for 
the lateral overflow, so to speak, of the ebb and correspond 
to the waste weirs or crevasses of a stream. 
CHARLESTON HARBOR. 
These characteristics are well illustrated in the harbor of 
Charleston, 8. C., as seen on the chart of 1858 (Big. i) 
I have selected this early date as it shows the current 
movements and condition of channels before extensive im- 
provements were begun. Here. the thalweg approaches the 
gorge ina direction nearly east and west, and on passing out 
it is deflected fully 90°, and extends nearly north and south. 
Hugging the northern spit is the flood channel, known as 
Maffit’s or Sullivan’s Island channel, with nine (9) feet on 
its crest at the daner end. Then appear the breakers of 
Jrunken Dick shoal, followed by the weir channels known as 
the North channel, with ten (10) feet at its ower end; the 
swash channel, nine (9) feet; the main ship channel, eleven 
(11) feet, and Lawford’s channel, ten (10) feet. 
The shortest distance to the outer eighteen (18) feet contour 
from the gorge is three arid one-fourth (34) statute miles, 
whilst by the main ship channel courses it is seven (7) miles, 
or more than double, so that vessels entering from the north 
must make a detour of nearly fourteen (14) miles to cross the 
bar. 
At the only current station outside the bar the set of the 
flood during the first and second quarters (its most energetic 
beriod) is parallel to the shore of Sullivan’s Island, or 
about west south- west, but it swings around through west 
to nearly north-west, or normal to the gorge during the 
last quarter. The stations inside of and on the bar show 
