the latter, the Delthyris arenosa, the peculiar fossil of the Oriskany sandstone, in the New York system, has been repeatedly identified. But from what locality this fossil has come, is unknown. A sandstone has been also found amongst this drift, perfectly resembling, in granular structure, mineral matter, and shade of color, the Seneca sandstone, of which the Smithsonian building is constructed. These resemblances, although sufficient to indicate probability of source, are not sufficient to identify it. The mineral contents, beside those already named, are mostly siliceous, and such as would result from the debris of the gneiss of the substratum of the neighborhood

HYDROGRAPHY.

The principal water-course in the District of Columbia is the Potomac River, which, taking its rise in the Alleghany Mountains, receives the waters of several important streams, and, after a winding course of about four hundred miles, discharges into Chesapeake Bay. The principal tributaries of the Potomac are the Shenandoah, the Monocacy, the Conococheague, and the Anacostia, or eastern branch of the Potomac.

The tide-water of the Potomac ceases at the Little Falls, a romantic succession of cascades, three miles above Georgetown. At the Washington Navy Yard the average. tide rises three feet, the Spring tide three and a half feet, and the neap two and a half feet. The southerly winds have a marked effect upon the height and continuance of the tides, and periodical freshets swell the volume of water. The Potomac is navigable as far as Greenleaf's Point, for the largest class of vessels, as is evidenced by

the approach of the British squadron when the Capital was captured, and by the fact that the American frigate Minnesota, which was built at the Washington Navy Yard, was safely launched and successfully navigated down the river to Chesapeake Bay. Between the Navy Yard and Georgetown the channel has been filled up with denudations from the upper valley of the Potomac, but it has been recently dredged by the corporations of Washington and Georgetown, at a heavy cost, and is now navigated by the large steamers which ply between Washington and New York.

Within the District, the principal tributaries of the Potomac are Rock Creek, which separates Washington, on the west, from Georgetown, and the Anacostia, or east branch of the Potomac. The latter is a tidal stream, once capable of bearing large ships, and, until within a few years, navigated by a smaller class of vessels as far as Bladensburgh.

The scientific surveys of the Potomac have not yet been sufficiently accurate to determine the velocity of the current created by the tidal wave, and other important data require the researches of the United States Coast Survey. From the Potomac the following marketable fishes are obtained, amongst which the shad and herring, because of their abundance, are, in an economical point of view, the most important: cat-fish, chub, eel, gar, herring, perch (white and yellow), pike, rock-fish, shad, sturgeon, suckers, sun-fish, and various other small species. Of sturgeon, specimens have been caught weighing over three hundred pounds.

ZOOLOGY.

Mammalia.-Whatever may have been the number of species of mammals inhabiting the District of Columbia in former times, the greater portion of them yet maintain a more or less permanent footing. Of those which formerly roamed over its surface, the wild cat (Lynx rufus), the panther, the American wolf, the black bear, the beaver, and perhaps the elk (Cervus Canadensis), are the only ones not found here at the present time, and it is even quite probable that the first-mentioned species still exists as a straggler. It is not probable that the buffalo ever lived in this region; the deer is not rare in the old ten-mile square; the otter even now is occasionally met with along the Potomac River, while foxes, rabbits, field mice, muskrats, and other species are more abundant than ever.

As far as accurate data are at our command, the following appear to be the characteristic features of the mammalian fauna of the District:

Of the Cheiroptera, or bats, about six species have hitherto been found. Of the Insectivora, there are three species of shrew mice, one of them a rare and little-known one, Sorex personatus. The common mole, Scalops aquaticus, and the star-nosed mole, Condylura cristata, also occur, the latter here finding its southern limit.

Of the Carnivora, two species of fox, the red and the gray, are abundant. The ermine weasel, Putorius Noveboracensis, although not rare, is not often taken. It is too far south here to assume its white, winter dress,-remaining. brown the whole year. The mink (Putorius vison) was also common until the rise in the value of its fur caused

increased attention to its pursuit and capture. The otter has been already referred to as occasionally found in the Potomac. The skunk (Mephitis mephitica) is almost as much a nuisance as ever. The raccoon is frequently brought into market, as is also the opossum (Didelphys Virginiana), the single representative of the Marsupialia.

Of the Rodentia, or gnawing animals, there are five kinds of squirrels, including the striped or ground squirrel and the flying squirrel. The most interesting species is the cat squirrel (Sciurus cinereus), a very large, heavy kind, occurring in different varieties of color, as red, gray, and black. It is confined to a limited area in Virginia, Maryland, Pennsylvania, Delaware, and New Jersey. The woodchuck (Arctomys monax) belongs to the same family with the squirrel.

Of other families of rodents, the jumping mouse, Jaculus Hudsonius, finds here nearly its southern limit. There are two long-tailed wild mice, Hesperomys leucopus and Nuttalli; and it is probable that the wood rat, Neotoma Floridana, was once found here.* Of the short-tailed field mice, one (Arvicola riparia) is the most abundant, the A. pinetorum, or pine mouse, being rare. The muskrat, the common rabbit (Lepus sylvaticus), and the Virginia deer, the latter the only ruminant, complete the catalogue.

Three species of rats and one of mice have been introduced into the district from Europe, making the total number of species now found to be 37. Adding at least five species formerly abundant, but now exterminated, we have 42 in all.

* It has very recently been sent to the Smithsonian Institution, from Loudon County, Virginia.

Ornithology. The District of Columbia, by reason of its situation between the northern and southern portions of the country, seems designed by nature to be the locality where the species peculiar to each section may meet, as, for a similar reason, it has been selected to be the political centre of the United States. Its situation with regard to east and west may be said to be, in a measure, central— equally distant on the one hand from the ocean with which it is connected by the broad waters of Chesapeake Bay and the Potomac River, and on the other from the extensive ranges of mountains lying directly to the westward. If, in addition to the advantages resulting from this central location, we take into consideration those arising from the varied character of its surface, and that of the adjacent country, we cannot but be struck with its peculiar adaptation to the habits of many and various species. We may expect to find within its limits a large proportion of the birds composing the eastern fauna of our country. And this, indeed, is the case. With the exception of those hardy birds fitted by nature to endure. the rigorous climate of the high latitudes, which seldom or never leave the hyperborean regions of the north, and those delicate species which are Summer visitants to our southern States from more tropical countries, there are few birds composing the eastern fauna which are not, at certain seasons, to be found within its borders. It forms the natural limit to the further progress of many more southern birds.

The Summer red-bird (Pyranga æstiva), the cardinal grosbeak (Cardinalis Virginianus) the celebrated Mocking-bird (Mimus polyglottus), Henslow's Bunting (Coturniculus Henslowi), and some others, do not proceed