according to age; it is stated that the full number in the adult dentition of H. australis is twenty-four, and twenty in H. dugong.

The habits of all the sirenians, so far as is known, are essentially similar, the dugong as well as the manatee being found around the mouths and up the water courses of the coast.

This order affords a most striking instance of the discovery and speedy extinction of a species, the Rhytina borealis, or stelleri of some authors, having been discovered on Behring's island in the sea of Kamschatka, by one of Behring's exploring parties, which was shipwrecked there in 1741. They existed in large numbers, were easily killed, and during the ten months which the shipwrecked party spent on the island, sad havoc was made among the animals. They were rapidly reduced in numbers, and in 1768, twenty-seven years after they became known to civilized man, the last one was killed. Almost all that is known of the living animal is from an account published in 1751, at St. Petersburg, by Steller, who was one of the discovering party, and who saw it in its native haunts.

The Rhytina was about twenty-five feet long, had a forked tail like that of the dugong, and was covered with a rough, wrinkled, brownish hide nearly an inch thick, composed of hair-like tubes agglutinated together into a substance somewhat like horn, and of so great toughness that it scarcely yielded to a blow of an axe. The adult animal was entirely devoid of teeth, and had in their stead a rough horny plate on the front of the palate, to which was opposed a similar one on the lower jaw.

The Sirenia are of considerable value to the natives of the countries which they inhabit; the hide is of use for making a thick leather, and the flesh is much esteemed for the table. It is said that the church, disagreeing with nature and science, determines that the manatee is a fish, and therefore the good Catholics of South America feast royally on its flesh on Friday and all other fast days.

AN EXAMINATION OF PROF. LEO LESQUEREUX'S THEORY OF THE ORIGIN AND FORMATION OF PRAIRIES.

F

BY O. P. HAY.

OR many years past there has been no lack of literature on the subject of the prairies of the western states and territories, nor any dearth of theories to account for their origin. We. have had their existence ascribed to fire and to water; to heat and to cold; to all sorts of phenomena and to the lack of them. The forests that once clothed these regions must have been burned up by prairie fires-before the prairies existed. They must have been drowned out by the waters of vast inland lakes that once covered these prairie states They must have been parched up up by the dryness of the climate. They must have been smothered by the impalpable fineness of the soil in which they grew. They never had an existence; because the seeds which ought to have produced them must have been ground to pomace by the glaciers of the Age of Ice, or hopelessly buried beneath their debris.

Prof. Leo Lesquereux, eminent in both recent and fossil botany, has published various papers on this subject, the latest of which appears in Vol. I. of the Illinois Geological Survey. In subsequent volumes of this excellent Survey this paper is frequently referred to; and certain phenomena observed in various portions of the state by the members of the survey corps, are cited as helping to establish Prof. Lesquereux's theory.. As this scientific work will have a wide circulation amongst geologists; and since, on account of the high reputation of Prof. Lesquereux as a scientist, his opinions will have great weight in determining people's opinions concerning an important geological feature of the West, it is proposed in this paper to examine the grounds upon which the theory has been based, and to test its correctness. For the writer believes that the theory is insufficient to account for all the facts involved-is, indeed, opposed by many of them; and that those examples which have been cited by the geologists as confirming the theory, instead of so doing, are excellent proofs of the way in which prairies have not had their origin.

Prof. Lesquereux believes the failure of forest vegetation to occupy the praries to be due to the chemical nature of the soil, coupled with, as it would seem from his language, its exceeding fineness. He believes that all our prairies and Western plains, as well as the plains of South America, Europe and Asia, have been

formed as we may now see prairies of far less extent being produced along the shores of the lakes of the West and along the banks of rivers. "Where the waves or currents strike the shores or the low grounds and there heap material, sand, pebbles, mud, etc., they build up more or less elevated dams or islands. These dams are not always built along the shores, but often enclose wide shallow basins, whose waters are thus sheltered against any movement. Here the aquatic plants, sedges, rushes, grasses, etc., soon appear, these basins become swamps, and, as it can be seen near the borders of Lake Michigan, though the waters may surround them, the trees never invade them, never grow upon them, even when the swamps become drained and dried by some natural or artificial cause." Prof. Lesquereux states that such marginal swamps, generally fringed with trees, can be seen also along the shores of Lake Erie, and along the Mississippi and Minnesota rivers, outside the line of slack water. All gradations are to be found between such swamps and dry prairies. He hence concludes that all our prairies, not only the low prairies along our lakes and rivers bottoms, but also the high rolling prairies, have been produced by the slow recess of sheets of water of various extent; that these lakes have first been transformed into swamps and by and by drained and dried. The soil of these ancient swamps, having been produced by the slow and incomplete decomposition of aquatic plants, must be of impalpable fineness and thoroughly impregnated with ulmic acid; the former condition proving deleterious to the germination of the seeds of trees, the latter condition favoring the growth of the peculiar vegetation of the prairies.

But if the prairies were at one time swamps, why is their surface not now everywhere level, or nearly so? Or, if the existing elevations have been formed as low islands or dams in lakes, why are they not now wooded? Mr. Lesquereux believes that the surface was originally horizontal; but that it has been made to assume its present undulating character by the slow and long continued erosive action of water;-in short, that the broad, gently sloping valleys have been worn out by running waters as have the beds of our rivers and creeks; the difference being that in the former case the waters have had a very gentle, in the latter a more rapid motion.

Let us now consider the facts and argument presented by Prof. Lesquereux, to sustain his opinion.

And first, is it true that trees will not, as a general thing, grow in swamps, or in ground that has once been a stagnant marsh? That there are but few species of trees that will grow in swamps covered with stagnant water none perhaps will deny; but that these same swamps will not, after they have been drained and dried, allow the growth of arborescent vegetation remains to be proved. All of Prof. Lesquereux's arguments and citations of authorities in reply to Prof. Winchell's objections to the theory of excessive moisture, cover but this one point, viz., that trees will not grow on lands saturated with stagnant water, and leave unproved the other and most important statement that they will not grow there when the ground has become dry. Should this statement be true, we ought to find extensive prairies in many regions where prairies are rare; for instance, along our low Atlantic coast, and the delta of the Mississippi River. Especially ought we to expect to find such tracts along the Amazon, instead of finding there the densest forests on the globe.

Long ago, in the American Journal of Science, Prof. Dana, in writing on the origin of prairies, gave the results of his own observations made in the Mohawk valley, and cited observations made by Prof. Verrill in Maine and Labrador. In this article it is stated that in Maine the bottoms of the lakes are, near the shores, composed of black, soft, vegetable mud of great depth; and though sedges and rushes are found growing at the water's edge, various kinds of trees approach very near the shore, growing even where the supporting soil is soft and wet. In cases where lakes and bogs have been drained, although grasses and sedges may get the mastery the first year or two, forest trees afterward gain the ascendency and keep it. In Labrador, trees were found growing in peat bogs, in the very borders of lakes and pools of stagnant waters. If trees will grow in stagnant marshes and on peat bogs in Maine and Labrador and are not found growing in similar situations in the Mississippi Valley, some other explanation of the fact must be sought than the chemical nature or the fineness of the soil.

But I believe that even in the Mississippi Valley we shall have no difficulty in finding luxuriant forests in situations where, according to Prof. Lesquereux, we ought to find only prairies; nor difficulty in finding prairies where we should be led to expect to find abundant timber. The soil of the Mississippi flood-plain has been deposited as in the case of other large rivers. In some

places strong currents have washed together coarse sands and gravels; in others, where the water has had a gentle movement, it has deposited only the finest sediment; the greater portion of the bottoms, however, consists, as we might expect, of a mixture of these materials, enriched by the humus from decaying vegetation. There has been no lack of opportunities for the formation of swamps in these bottoms, which are frequently from four to eight miles or more in width. Nevertheless, on these bottom lands, formed to a great extent in the way described by Prof. Lesquereux, and much more recently than can be claimed for the higher prairies, we find the heaviest growth of timber and the greatest proportion of timber land.

In the southern part of the State, where upland prairies do not exist, the flood-plain is clothed with the densest growth of forest trees; and this almost irrespective of the character of the soil. In Alexander county, for instance, as stated in the Report of the Illinois State Geological Survey, "the bottom lands are generally flat and are interspersed with cypress ponds and marshes." The higher bottoms are said to be heavily timbered with various kinds of trees. "The swampy lands are characterized by the growth of the cypress, sweet gum, tupelo gum, cottonwood, pecan, willow,

We find analogous statements made concerning the counties lying northward along the Mississippi, until we reached the region where prairies begin to appear on the highlands. Then small prairies appear also on the flood-plain; but these are likely to occupy the higher grounds and the dense timber growth the low wet lands. We learn of heavy forests on soil described as a deep sandy loam, highly charged with humus; and on similar soils, bottom prairies. Nor is it unusual along the Mississippi and other rivers of Illinois to find bottom prairies whose soil contains a large proportion of sand and gravel. In the report of the geology of Jo Daviess county, the most northern river county of the State, we find this statement : In the western part of the township of Hanover, bottom timber-land, alluvial grass-land, and a table-land, high and dry, exhibit all the characteristics of the ordinary Mississippi alluvial bottoms. Farther down in Carroll county this bottom changes into the broad, well-known sand prairie, an old, broadly extended, glittering Mississippi sand-bar." Such quotations from many independent observers could be multiplied indefinitely to show: Ist. That even marshes may be timber-grown; 2d. That the distribution of forest lands bears