occur in different regions of our own and other countries, with the alternate changes of freezing and melting-or larger and smaller masses of water; and these changes he thought would be sufficient to move any masses of snow and ice over the flattest surface-even over hills and mountains, if the mass possessed sufficient momentum.

Now where do we observe these scratched and polished surfaces? On the tops of mountains, and the highest hills; yes, on their very summits. He then attributed these effects to the agency of icealthough, to a great extent, there are other phenomena which must arise from the action of water.

Prof. AGASSIZ also made remarks upon—

THE BLACK BANDED CYPRYNIDE.

He observed that the markings, (the black bands,) usually considered so characteristic of the species, go for nothing, when we find that these bands are only observable in the young, and that they are gradually obliterated.

He next proceeded to say, that it was necessary to separate from the family of Cyprynidæ, those which he denominated Cyprynodonts. He illustrated his meaning by the black-board. The difference was -that the former had an additional tubercle behind the cerebellum; but in the Cyprynodonts, we have a simple brain without the tubercle.

The next subject was a few observations by Prof. AGASSIZ, on the

MONOGRAPH OF GARPIKES.

He said, it would be recollected, that in the Pliocene, or New Red Sandstone of Connecticut, great numbers of fossils have been found, in various stages of preservation. He had thought it expedient to examine monographically the present existing species of fishes, which closely resemble these fossils. The only types living, which bear a particular resemblance, are the Garpikes. These have been distinguished by several different species, but he had divided the genus Lepidostesces, (the Garpikes,) into two types-the sharp-nosed and the flat-nosed. Yet he thought he had found three species, in this investigation, of the former, and also two or three of the latter, or flat-nosed. The details of these investigations, he continued,

would be of very little interest. He hoped, however, that they would soon be sufficiently developed to bring the attention of paleontologists to bear upon the subject. He referred to the structure of the brinoids-that is, those star fishes which, in their earlier stages of life, rest upon a stem. He demonstrated his meaning by the black-board. The star fishes, he said, when full grown, show apparently a quite different animal, caused by the formation of loose plates, arranged variously on the surface, and we notice a calcareous centre, whence the different rays diverge. The only difference discoverable was, that instead of these plates forming a series of loose particles, (as in the young,) they are united, in the full-grown animal, into hard developed rays, and the creature assumes its permanent form of a single star, instead of its former branched appearance.

Dr. R. W. GIBBES next presented a remarkable fossil, which he desired to refer to Prof. AGASSIZ for examination. Prof. A. being thus called upon, said he thought it extremely interesting, and that it seemed to bear a close resemblance to the great group of cartilaginous fishes, and thought it likely to indicate a new family, intermediate between the Saw fish (Pristis) and the Cestracionts. The locality, in the far west, is not certainly known, but it is most likely from the cretaceous.

Mr. T. GREEN exhibited and described some new forms of Rhamnus lanceolatus.

Prof. HUNT read a paper "ON ACID SPRINGS AND GYPSUM DEPOSITS OF THE ONONDAGA SALT GROUP," which has been published in the American Journal of Science and Arts, March, 1849, Prof. J. C. BooтH next presented a paper—

p. 175.

ON THE PHYSICAL GEOGRAPHY AND GEOLOGY OF THE NORTHERN PORTION OF THE STATE OF MISSISSIPPI. BY RICHARD BOLTON, Esq.

The region between the Mississippi bottom and the Tombigbee valley, presents ranges of hills of nearly uniform height, from 80 to 150 feet above the adjacent water-courses, the principal streams being about 18 miles apart. It may, therefore, be regarded as nearly level land, denuded by these water-courses. The water-courses have an upper or dry bottom; a lower wet bottom, subject to overflow in winter, and heavily timbered, and are usually from 1 to 200 feet wide. The valleys and broader hill-tops offer rich arable land to the

planter. Few rocks are visible on the surface, and gravel is rare; hence the streams have neither falls nor rapids.

Two lines, drawn from north to south, crossing the streams, one at the distance of 50 miles from the eastern boundary of the State, and the other 60 miles farther west, will divide the upper part of Mississippi into three belts, which may be denominated the calcareous, arenaceous and alluvial formations. The first embraces the Tombigbee valley and Prairies, including a small portion of the carboniferous series, in the N. E. corner of the State; the second, the hilly region, where sand-rock occasionally appears, and through which the watercourses, flowing west, suddenly turn south, and enter the third, or the Mississippi bottom.

1st Division.-A low ridge, striking off westward from the carboniferous hills, sweeps around the head of the Tombigbee valley, and turning south, bounds this valley on the west, and is the source of the streams flowing through the other divisions. To the east of the Tombigbee river the soil is red, and no rock is visible; nearer to the river, and partly on its west side, the soil is sandy and gravelly, and may be ascribed to the detritus of the carboniferous rocks in which the branches take their rise.

West of this, and reaching to the ridge just mentioned, is the Prairie region, of slight elevation, but sufficiently undulating for drainage, characterized by its rich, black soil, varying from 2 to 20 feet in depth. Commencing near the north limit of the State, and with an average width of 18 miles, it strikes south, about 200 miles, and then turns eastwardly into Alabama. It is underlaid by Rotten or Prairie limestone, which, near the town of Aberdeen, in N. Mississippi, has a thickness of 1 to 200 feet; but 12 miles further west, and in S. Alabama, attains a thickness of 900 feet, or more. It appears to dip slightly towards the south. The limestone is white, soft and amorphous, and crumbles readily on exposure to the air; where it appears on the surface it constitutes a "bald Prairie," destitute of herbage. Springs are rarely found issuing from this rock; and wells dug down to it, merely collect the rain-water, which, by percolation through the black soil, has a strong and disagreeable taste. To obtain pure water, artesian wells are sunk through this rock to the subjacent sand, and the water then rises to within 40 or 50 feet of the surface. In similar wells, in S. Alabama, it rises even to 20 feet above the surface.

To the west of the Prairie region lies the ridge first mentioned, which, with its spurs, has an average width of 10 miles. It is com

posed of a red loam, 25 feet deep, lying upon sand of 30 feet thickness; and this, again, reposing upon a hard, light gray limestone. The rock contains about one quarter sand, burns readily to lime, and seems to be almost wholly composed of gryphæa. It also contains an abundance of echinus and spatangus. The region abounds with springs of pure water, issuing from the sand above the limestone. Spurs, running south-east from the ridge, diminish in height, and occasionally show the rotten limestone near the surface. Their uniformity of slope is remarkable. The streams run south-east, and, in crossing them from south to north the ascent, to the summits of the spurs, is very gradual, but then the descent is very abrupt to the next The springs occur chiefly on this abrupt slope.

stream.

2d Division. Following the streams issuing from the red loam ridge, in their west course, the first strip, of some 8 miles width, is a kind of valley between the red ridge and the following sandstone ridges. Its soil is a grayish, sometimes sandy clay, and mostly covered with post-oak, and unproductive, excepting in some rich black bottoms. It seems to be on a level with the hard limestone, is destitute of springs; its streams are sluggish, and water can rarely be obtained by digging.

The next belt, of 10 miles width, consists of broken, intricate, sandy ridges, frequently capped by red sandstone, and covered with pine trees. Fresh water springs abound in the hollows; a feeble chalybeate is sometimes found, and, more rarely, a sulphur spring. Petrified wood and coal (lignite?) occur, the latter in thin strata.

The following belt, of 20 miles width, is arable, and characterized by long, level, dry sandy valleys, by numerous springs and free flowing streams of pure water. The soil is a light vegetable mould. The tops of the ridges, more or less level and fertile, are composed of a light coloured loam, of 10 to 20 feet depth, resting on a quicksand of unknown depth (over 100 feet).

The last belt has an ash-coloured soil, approaching that of the Mississippi bottom, with compact sand and some gravel, and a sandstone rock, showing itself here and there. Springs are scarce, and wells on the ridges are often sunk to the level of the Mississippi river. The ridges of this belt subside by steep descents of 80 or 120 feet, to the Mississippi bottom.

This 3d Division, or the Mississippi bottom, extends from Memphis to Vicksburg, 180 miles in length, and is 60 miles wide in the middle, tapering towards each end. Its features are too well known to require description.

K

The divisions, and even the subdivisions, given above, are not only characterized by their topography, geology and soil; but, as might be inferred by the peculiar kind of forest covering them, hickory, pine, and various kinds of oak. We are struck with the complete and regular system of drainage; the size of the streams and their valleys being always proportional to the extent of country drained. It is evident, from this fact, conjoined with the character of the formations, that the whole has been quietly and simultaneously elevated, and has not materially suffered by subsequent subterranean action. It appears, further, that the Prairie belt, east of the red loam ridge, and the clay belt west of the same, were two marine valleys, and that the remainder of the country constituted a great level, probably with a very gentle southern slope, which, as the land rose, was scooped into hill and valley, with the peculiar features which are its present characteristics. The Section then adjourned till Monday.

R. W. GIBBES, Secretary.

September 23.

SECTION OF GENERAL PHYSICS, &c.

Third Meeting.

On motion, Lieut. M. F. MAURY, U. S. N., was called to the chair. A paper was read "ON CHEMICAL PHILOSOPHY." By Mr. T. S. HUNT.

This paper has been published in the American Journal of Science and Arts for May, 1849.

A paper was read by Prof. JAMES H. COFFIN "ON THE MEAN VALUES OF DIFFERENT POWERS OF THE RADII VECTONES OF THE ELLIPSE," in which he showed—

1st. That the mean value of their first powers is equal to the semitransverse axis.

2d. That the mean value of their squares is equal to the square of the semi-transverse axis, plus half the square of the eccentricity.

3d. That the mean value of their cubes is equal to the cube of the semi-transverse axis, plus the square of the eccentricity, multiplied by three-fourths of the transverse axis.

Prof. M. H. Boyè's paper, "ON THE COMPOSITION OF BITTERN," was now read. It has been published in the American Journal of Science and Arts for January, 1849.