184 ANCIENT SUBSIDENCE OF DELTA. [CHAP. XXX. 



ground was raised vertically to the same amount by 

 fluviatile mud, sand, or vegetable matter. But if the 

 land should go down even ten or twelve feet at 

 once, the whole delta would be submerged beneath 

 the sea. Were the downward movement here sup 

 posed to be followed by an upheaval to the extent of 

 about 150 feet, and should the river then cut a chan 

 nel through the upraised mass, we might expect to 

 see the modern formation exhibit appearances similar 

 to those of high antiquity above described at Port 

 Hudson. 



I shall endeavour, in the sequel, to show that oscil 

 lations of level, like those here assumed to account 

 for the phenomena at Port Hudson, will explain 

 other appearances, observable, not only in cliffs 

 bounding the valley of the Mississippi, but in ancient 

 alluvial terraces bordering the Ohio, and other tribu 

 taries of the great river. 



