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high-water mark down to at least twenty-five feet below, measuring out a time when not less than ten fully matured cypress growths must have succeeded each other, the average of whose age could not have been less than four hundred years, thus making an aggregate of 4000 years since the first cypress tree vegetated in the basin. There are also instances. where prostrate trunks, of huge dimensions, are found imbedded in the clay, immediately over which are erect stumps of trees numbering no less than 800 concentric layers." But the skeleton referred to was found under four of these "buried forests," or "cypress growths;" so that, according to the mode of calculation here proposed, its antiquity is only 1600 years. And we venture to suggest, what to our view is at least equally probable, that if it was sunk in the soft mud of the swamp, or in some ancient grave, it may have reached the place where it was found even within the time since Europeans settled in the country.

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Sir Charles Lyell is inclined to think the delta of the Mississippi very ancient. "Although we can not estimate correctly how many years it may have required for the river to bring down from the upper country so large a quantity of earthy matter, the data for such computation being as yet incomplete, - we may still approximate to a minimum of the

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time which such an operation must have taken, by ascertaining, experimentally, the annual discharge of water by the Mississippi, and the mean annual amount of solid matter contained in its waters. The lowest estimate of the time required would lead us to assign a high antiquity, amounting to many tens of thousands of years (probably more than 100,000), to the existing Delta.” (p. 43.) But a recent "Report upon the Physics and Hydraulics of the Mississippi River," by Captain A. A. Humphreys, and Lieutenant H. L. Abbot, of the United States Topographical Engineers, states that it is apparent " from many considerations, that the mouth of the river was once more than two hundred miles above where it now is, and that it is building out into the gulf new land at the rate of 262 feet every year." Assuming this as the basis of calculation, we find but little more than 4000 years requisite for the formation of the Delta from at least one hundred miles above New Orleans. Still another estimate is that of Major Stoddard, in a treatise on the State of Louisiana,† who says, "It is calculated that from 1720, a period of eighty years, the land has advanced fifteen miles into the sea; and there are those who assert that it

* N. Am. Rev. for April, 1862.

† Quoted in "Campaign to the Rocky Mountains,” p. 240, by James Hildreth.

has advanced three miles within the memory of middle-aged men.” These data give an increase of 990 feet in a year, requiring no more than 1160 years for the formation of the entire Delta.

These methods of computation are all too uncertain to have any value in discussions like this. Many geologists frankly confess that they are wholly unreliable. "Many ingenious calculations," says Page,* * have, no doubt, been made to approximate the dates of certain geological events; but these, it must be confessed, are more amusing than instructive. For example, so many inches of silt are yearly laid down in the Delta of the Mississippi — how many centuries will it have taken to accumulate a thickness of 30, 60, or 100 feet? Again, the ledges of Niagara are wasting at the rate of so many feet per century—how many years must the river have taken to cut its way back from Queenstown to the present falls? . . . For these and similar computations, the student will at once perceive we want the necessary uniformity of factor; and, until we can bring elements of calculation as exact as those of astronomy to bear on geological chronology, it will be better to regard our 'eras,' and 'epochs,' and systems,' as so many terms, indefinite in their

* Advanced Text-book of Geology, by David Page, F. G. S. Edinburgh, 1861, p. 385.

duration, but sufficient for the magnitude of the operations embraced within their limits."

4. Sir Charles Lyell mentions, but does not dwell upon, an alleged discovery of human remains in certain coral reefs on the coast of Florida. These reefs are in a process of growth by which it is estimated that the land advances upon the sea at the rate of one foot in a century. "In a calcareous conglomerate forming part of the above-mentioned series of reefs, and supposed by Agassiz, in accordance with his mode of estimating the rate of growth of those reefs, to be about 10,000 years old, some fossil human remains were found by Count Pourtalis. They consist of jaws and teeth, with some bones of the foot." (Geol. Ev. p. 44.) This case is too indefinite to have any value. Nothing is stated as to the position of these remains, or the reasons for attributing to them an antiquity equal to that of the reef itself. For aught that appears, they may be of a similar class with the famous Guadaloupe skeleton found in a ledge of shell limestone now in process of formation on the shore of that island, which is now ascertained to be the remains of a Carib Indian killed in battle about two hundred years ago.*

5. But the case most relied on to prove the re

* Dana's Manual of Geology, p. 580.

mote antiquity of man on earth appears to be that of the discovery of flint implements, constructed by man, in certain beds of river drift, accompanied by the remains of ancient animals in the valley of the Somme, in Picardy, France.

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The above diagram will aid us in comprehending the phenomena of this valley. "It is situated geologically in a region of white chalk, with flints, the strata of which are nearly horizontal. The chalk hills which bound the valley are almost everywhere between 200 and 300 feet in height. On ascending to that elevation, we find ourselves on an extensive table-land, in which there are slight elevations and depressions. The white chalk itself is scarcely ever exposed at the surface on this plateau, although seen on the slopes of the hills as at a and b. The general surface of the upland region is covered continuously for miles in every direction by loam or brick earth (5), about five feet thick, devoid of fossils. To the wide extent of this loam the soil of Picardy chiefly owes its great fertility: Here and there we also observe on the chalk outlying patches of tertiary sand and clay (6), with eocene fossils, the remnants

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