Haupt. | 22 [Dec. 16, 
local modifications of the ‘flood and a movement towards the 
entrance, due to the diminution of resistance in that direction, 
especially during the last quarters of the flood. The plane of 
maximum ebb scour, as indicated by the depth of water on 
the bar, is limited to about twelve (12) feet. 
Similar features will be noticed at Galveston (Fig. 2) 
and at other entrances, but it does not always happen that the 
crossing of the bar isso far from the gorge, nor is it always to the 
south. The position of this important pointis the resultant of the 
internal and external forces which affect the movement of the 
main ebb stream. 
THE FORCES. 
The internal forces are those resulting from the form and 
extent of the inner basin, the volume of the tidal prism and 
the relative directions of the tidal and river currents as they 
approach the gorge. The external effects are those resulting 
from the form, position and extent of the banks which have 
been piled up by the flood and obstruct the ebb. Hence it fol- 
lows, if the flood pressure and movement is from the south 
side of the entrance the channel will be to the north, as the 
banks will be more extensive on the former side, offering 
greater resistance and deflecting the ebb stream and crowding 
it in until it is supported on its opposite flank by the shore. If 
the flood resultant comes in from the northern side, the reverse 
is true. 
Again, if the confluent ebb streams of the inner basin are so 
directed by natural or artificial constructions as to commingle 
and unite their energies, instead of opposing one another, as most 
frequently occurs, the momentum of the united stream will be 
greater and the crossing on the bar be consequently deepened. 
This will be better understood by observing that the inner 
