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1846, I cannot form an opinion as to the value of the chronological calculations which have led Dr. Dowler to ascribe to this skeleton an antiquity of 50,000 years. In several sections, both natural in the banks of the Mississippi and its numerous arms, and where artificial canals had been cut, I observed erect stumps of trees, with their roots attached, buried in strata at different heights, one over the other. I also remarked, that many cypresses which had been cut through, exhibited many hundreds of rings of annual growth, and it then struck me that nowhere in the world could the geologist enjoy a more favourable opportunity for estimating in years the duration of certain portions of the recent epoch.*
Coral Reefs of Florida. Professor Agassiz has described a low portion of the peninsula of Florida as consisting of numerous reefs of coral, which have grown in succession so as to give rise to a continual annexation of land, gained gradually from the sea in a southerly direction. This growth is still in full activity, and assuming the rate of advance of the land to be one foot in a century, the reefs being built up from a depth of seventy-five feet, and that each reef has in its turn added ten miles to the coast, Professor Agassiz calculates that it has taken 135,000 years to form the southern half of this peninsula. Yet the whole is of post-tertiary origin, the fossil zoophytes and shells being all of the same species as those now inhabiting the neighbouring sea. 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 CHAP. II. RECENT DEPOSITS OF SEAS AND LAKES. 45 fossil human remains were found by Count Pourtalis. They consisted of jaws and teeth, with some bones of the foot.
* Dowler, cited by Dr. W. Usher, in Nott and Gliddon's Types of Mankind, p. 352.
p Agassiz, in Nott and Gliddon, ibid. p. 352.
Recent Deposits of Seas and Lakes. I have shown, in the Principles of Geology, where the recent changes of the earth illustrative of geology are described at length, that the deposits accumulated at the bottom of lakes and seas within the last 4000 or 5000 years can neither be insignificant in volume or extent. They lie bidden, for the most part, from our sight; but we have opportunities of examining them at certain points where newly-gained land in the deltas of rivers has been cut through during floods, or where coral reefs are growing rapidly, or where the bed of a sea or lake has been heaved up by subterranean movements and laid dry.
As examples of such changes of level by which marine deposits of the recent period have become accessible to human observation, I have adduced the strata near Naples in which the Temple of Serapis at Pozzuoli was entombed. These upraised strata, the highest of which are about twenty-five feet above the level of the sea, form a terrace skirting the eastern shore of the Bay of Baiæ. They consist partly of clay, partly of volcanic matter, and contain fragments of sculpture, pottery, and the remains of buildings, together with great numbers of shells, retaining in part their colour, and of the same species as those now inhabiting the neighbouring sea. Their emergence can be proved to have taken place since the beginning of the sixteenth century.
In the same work, as an example of a fresh-water deposit of the recent period, I have described certain strata in Cashmere, a country where violent earthquakes, attended by
* Principles of Geology, Index, “Serapis.'
alterations in the level of the ground, are frequent, in which fresh-water shells of species now inhabiting the lakes and rivers of that region are embedded, together with the remains of pottery, often at the depth of fifty feet, and in which a splendid Hindoo temple has lately been discovered, and laid open to view by the removal of the lacustrine silt which had enveloped it for four or five centuries.
In the same treatise (ch. xxix.) it is stated, that the west coast of South America, between the Andes and the Pacific, is a great theatre of earthquake movements, and that permanent upheavals of the land of several feet at a time have been experienced since the discovery of America. In various parts of the littoral region of Chili and Peru, strata have been observed enclosing shells in abundance, all agreeing specifically with those now swarming in the Pacific. In one bed of this kind, in the island of San Lorenzo, near Lima, Mr. Darwin found, at the altitude of eighty-five feet above the sea, pieces of cotton-thread, plaited rush, and the head of a stalk of Indian corn, the whole of which had evidently been embedded with the shells. At the same height, on the neighbouring mainland, he found other signs corroborating the opinion that the ancient bed of the sea had there also been uplifted eighty-five feet since the region was first peopled by the Peruvian race. But similar shelly masses are also met with at much higher elevations, at innumerable points between the Chilian and Peruvian Andes and the sea-coast, in which no human remains have as yet been observed. The preservation for an indefinite period of such perishable substances as thread is explained by the entire absence of rain in Peru. The same articles, had they been enclosed in the permeable sands of an European raised beach, or in any country where rain falls even for a small part of the year, would probably have disappeared entirely.
In the literature of the last century, we find frequent allu
CHAP. III. UPHEAVAL OF CENTRAL DISTRICT OF SCOTLAND.
sion to the era of existing continents,' a period supposed to have coincided in date with the first appearance of Man upon the earth, since which event it was imagined that the relative level of the sea and land had remained stationary, no important geographical changes having occurred, except some slight additions to the deltas of rivers, or the loss of narrow strips of land where the sea had encroached upon its shores. But modern observations have tended continually to dispel this delusion, and the geologist is now convinced that at no given era of the past have the boundaries of land and sea, or the height of the one and depth of the other, or the geographical range of the species inhabiting them, whether of animals or plants, become fixed and unchangeable. Of the extent to which Auctuations have been going on since the globe had already become the dwelling-place of Man, some idea may be formed from the examples which I shall give in this and the next nine chapters.
Upheaval since the Human Period of the Central
District of Scotland. It has long been a fact familiar to geologists, that, both on the east and west coasts of the central part of Scotland, there are lines of raised beaches, containing marine shells of the same species as those now inhabiting the neighbouring sea.* The two most marked of these littoral deposits occur at heights of about forty and twenty-five feet above high-water mark, that of forty feet being considered as the more ancient, and owing its superior elevation to a longer continuance of the upheaving movement. They are seen in some places to rest on the boulder clay of the glacial period, which will be described in future chapters.
* R. Chambers, Sea Margins ;' 1848, and papers by Mr. Smith of
Jordan Hill, Mem. Wern. Soc. vol. viii., and by Mr. C. Maclaren.
In those districts where large rivers, such as the Clyde, Forth, and Tay, enter the sea, the lower of the two deposits, or that of twenty-five feet, expands into a terrace fringing the estuaries, and varying in breadth from a few yards to several miles. Of this nature are the flat lands which occur along the margin of the Clyde at Glasgow, which consist of finely laminated sand, silt, and clay. Mr. John Buchanan, a zealous antiquary, writing in 1855, informs us, that in the course of the eighty years preceding that date, no less than seventeen canoes had been dug out of this estuarine silt, and that he had personally inspected a large number of them before they were exhumed. Five of them lay buried in silt under the streets of Glasgow, one in a vertical position with the prow uppermost as if it had sunk in a storm. In the inside of it were a number of marine shells. Twelve other canoes were found about a hundred yards back from the river, at the average depth of about nineteen feet from the surface of the soil, or seven feet above high-water mark; but a few of them were only four or five feet deep, and consequently more than twenty feet above the sea-level. One was sticking in the sand at an angle of 45°, another had been capsized, and lay bottom uppermost; all the rest were in a horizontal position, as if they had sunk in smooth water. *
Almost every one of these ancient boats was formed out of a single oak-stem, hollowed out by blunt tools, probably stone axes, aided by the action of fire; a few were cut beautifully smooth, evidently with metallic tools. Hence a gradation could be traced from a pattern of extreme rudeness to one showing great mechanical ingenuity. Two of them were built of planks, one of the two, dug up on the property of Bankton in 1853, being eighteen feet in length, and very elaborately constructed. Its prow was not unlike the beak of an antique
* J. Buchanan, Brit. Ass. Rep. 1855, p. 80; also Glasgow, Past and Present, 1856.