228 ANNUAL OF SCIENTIFIC DISCOVERY. 



The age of stumps and erect trunks of the deciduous cypress, 

 whether living or buried, retaining their natural positions at points 

 near the present termination of the delta, ought to be carefully exam- 

 ined, as they might afford evidence of the minimum of time which 

 can be allowed for the gain of land on the sea. Some single trunks 

 in Louisiana are said to contain from 800 to 2,000 rings of annual 

 growth, and Messrs. Dickeson and Brown show that in some filled-up 

 cypress basins, 4,000 years must have passed since the first cypress- 

 tree vegetated in them. 



After considering the age and origin of the modern deposits of the 

 Mississippi and its tributaries, we have still to carry back our thoughts 

 to the era of the fresh-water strata seen in the bluffs which bound the 

 great valley. These in their southern termination have evidently 

 formed an ancient coast line, beyond which the modern delta has been 

 pushed forward into the sea. From the loam at Natchez and in other 

 localities, from the remains of associated terrestrial animals, and from 

 the buried trees at Port Hudson, we have inferred that these deposits 

 are the monuments of an ancient alluvial plain of an age long anteri- 

 or to that through which the Mississippi now flows, which was inhab- 

 ited by land and fresh-water mollusca, agreeing with those now ex- 

 isting, and by quadrupeds, now for the most part extinct. 



In my former work I described some ancient terraces occurring in 

 the valley of the Ohio, and pointed out that the included fossil-shells 

 demonstrate the fluviatile and modern origin of the deposits, and sug- 

 gested that their present position could only be explained by suppos- 

 ing, first, a gradual sinking down of the land, after the original exca- 

 vation of the valley, during which period the gravel and sand were 

 thrown down, and then an upheaval of the same valley, when the 

 river cut deep channels through the fresh-water beds. By simply 

 extending to the valley of the Mississippi the theory before applied 

 to that of the Ohio, we may account for the geological appearances 

 seen in the larger and more southern area. 



In regard to the time consumed in accomplishing the great oscilla- 

 tion of level, which first depressed so large an area to the depth of 

 200 feet or more, and then restored it to its former position, it is im- 

 possible, in the present state of science, to form more than a conjec- 

 ture as to the palpable mean rate of movement. To suppose an av- 

 erage sinking and upheaval of two and a half feet in a century, might 

 be sufficient, or would, perhaps, be too great, judging from the mean 

 rate of change in Scandinavia, Greenland, the north of the Adriatic, 

 and other regions where similar changes are now going on, or have 

 been so recently. Even such an oscillation, if simultaneously contin- 

 uous over the whole area, first in one direction, and then in another, 

 and without any interruptions or minor oscillations, would require 

 16,000 years for its accomplishment. But the section at Cincinnati 

 seems to imply two oscillations, and there would probably be pauses, 

 and a stationary period, when the downward movement ceased, and 

 was not yet changed into an upward one. Nor ought we to imagine 

 that the whole space was always in motion at once. Condensed from. 

 LyelTs Second Visit to the United States. 



