and the broad but slow currents of the tortuous streams never free the swamps and lowlands of their superfluous water. So level is the country and so abundant the supply of water, that the engineering skill and outlay required to perfect its drainage would, at comparatively small additional outlay, render the larger part of the surface susceptible to cultivation by irrigation. In connection with drainage and the embankment of the rivers, the assertion is frequently made, that such works are less practicable now than formerly, when they were attempted in consequence of the increased size and frequency of freshets, resulting from cutting down the forests, the chief obstructions to the rapid passage of rain water into the streams. In the absence of records giving exact data on this point, this assertion rests more on the apparent nature of the case than on ascertained facts. On the contrary, nothing can be more certain than that no subsequent freshet has attained the height and extent of the great flood of 1796, known as the Yazoo freshet, and that none has exceeded the May freshet of 1840.

GEOLOGICAL FEATURES.

Out-crops of the cretaceous rocks of the secondary formation occur east of the Santee river, in numerous localities in the Lower Pine Belt of South Carolina. Commencing at Little river, in the southeastern corner of Horry county, Prof. Tuomey followed these rocks to Mars Bluff on the Great Pee Dee and to points as far north as Darlington C. H. They make their appearance on Lynches river in about the same latitude, and were traced by Mr. Ruffin as far west as Kingstree, the county seat of Williamsburg. They consist of a soft marl of a dark gray color, containing (as at Mars Bluff) the remains of belemnites in great number. This marl averages about 34 per cent. of carbonate of lime, and rests on a stratum of hard lime or marl stone, which yields 75 per cent. of carbonate of lime. The marl stone in turn rests on a black shale of laminated clay, which rests on beds of sand. The buhr-stone reaches down into the Lower Pine Belt in several localities along its northwestern edge. Prof. Tuomey thought he had traced it as far as the Ashepoo river in Colleton and to Huspa creek in Beaufort county. But as the rocks he referred to are now recognized as belonging to the phosphate rock formation, the buhr-stone does not extend so far south as he supposed.

The body of the Lower Pine Belt is underlaid by marl belonging to that portion of the eocene formation of the tertiary, designated by Mr. Ruffin the Great Carolina Bed. These marl beds are divided into two well-marked groups, known as the Santee marls and as the Ashley and Cooper river marls. The Santee marls are the older, lower and more ex

tensive formation. Reaching from Mazyck's ferry on the Santee in Charleston county to Vance's ferry on that river in Orangeburg county, and underlying nearly the whole of Clarendon county, they have been traced along Potato creek as far north as Sumter county. Westward they extend through Colleton, Orangeburg, Hampton and Barnwell counties, to the Savannah river; reaching as high up on that stream as Shell bluff, a noted locality in Burke county, Ga. Their northern margin rests on the buhr-stone, and to the west and south they pass under the Ashley and Cooper marls. The Santee marls form the lowest member of the calcareous strata of the Charleston basin, and was designated by Prof. Tuomey the Coralline bed of the Charleston basin, being composed of the remains of corals and gigantic oyster shells. It consists of strata of soft marl, marl-stone and green sand, and is very rich in carbonate of lime, averaging 90 per cent. of that valuable ingredient of the soil.

Resting on the Santee marls, and passing out with them beneath the pleiocene and post-pleiocene of the coast under the sea to a great depth, are the Ashley and Cooper marls. Unlike the Santee marls, they contain neither corals or oyster shells, but are composed of minute many chambered shells (Polythalamia and Foraminfera). These marls are of a dark gray color and granular texture, sometimes so compact as to render the material suitable for building purposes. Prof. Tuomey mentions at ruined house, erected long ago, by Sir John Colleton, of this material, which reminded him of Portland stone. The marks of the tools upon the walls exposed to the weather were as well defined as if they had been impressed yesterday, and the angles of a tasteful mantelpiece, handsomely moulded and decorated, were as sharp, despite its long neglect, as when first executed. These marls are not so rich as the Santee marls and average only about 60 per cent. of carbonate of lime. They have long been known, however, to contain a notable quantity of phosphate of lime, and a great interest attaches to them, as it is the fragments broken from their irregular surface, and rounded by the waves, which have been converted into the nodules rich in phosphate of lime and known as

PHOSPHATE ROCK.

The deposits of phosphate rock occur over a wide range of country, reaching from North Carolina to Florida, and extending in some instances as much as 60 miles inland. Vertically, so far as their occurrence in quantities of value economically is concerned, their distribution is confined within narrow limits. They are found at the bottom of rivers, 20 to 30 feet in depth, and on land they occur at an elevation but slightly above mean high tide, so that the tides of the existing sea, supplemented

in a few instances perhaps by the action of storms, is sufficient to account for any movements that these water-worn nodules have undergone. The rock of commerce occurs always above the marl, and is known as the land or water rock, according as it is found in the one element or the other. The water rock is darker in color and harder than the land rock, and is frequently found in a layer or sheet of cemented or tightly compacted nodules, overlying the marl at the bottom of the rivers and creeks, where it either forms the bottom itself or is overlaid by a deposit of mud of greater or less depth. It has been seldom dredged for at a depth exceeding 20 feet. The land rock is found at a depth of 2 feet to 10 feet (and more under elevations) below the surface of the soil, but is not mined at a depth exceeding 5 to 7 feet. It is found in masses or nodules, varying from the size of a potato to several feet in diameter. These nodules are rounded, rough, indented, and frequently perforated with irregular cavities. They vary in color from olive or bluish black to a yellowish or grayish white. Their specific gravity is 2.2 to 2.5. Their hardness from 3.5 to 4. The fragments of a nodule give off a peculiar foetid odor on friction. By analysis it is found to contain phosphate of lime 55 to 61 per cent., carbonate of lime 5 to 10 and organic matter and water 2 to 10 per cent., with small quantities of fluorine, iron, magnesia, alumina and sulphuric acid, besides sand. The land rock is found in a loose layer, varying from a few inches to 30 in depth, averaging about 8 inches. It occurs in sand, mud, clay or peat, and is often intermingled with numerous remains of land and marine animals. Among the former are the remains of the mastodon, elephant, tapir, deer, and of our domestic animals, the horse, the cow and the hog. Thus showing that these very animals which were imported by the first white settlers had once inhabited this region, from which they had disappeared, so far as tradition informs us, before the advent of man, furnishing Prof. Agassiz with one of his strongest arguments in favor of "independent centres of creation." The remains of these land animals are found intermingled with, but never imbedded in, the phosphate rocks, giving no evidence that there was any community of origin between them. So abundant are the remains of marine animals that Mr. Toumey named this formation the "Ashley Fish Bed." Most striking among these remains are the beautifully preserved teeth of sharks, from 2 inches to 4 inches in length; if the proportions between the teeth and the body found among existing sharks obtained with these monsters, they must have been 60 feet to 80 feet in length. The sharks teeth, on the other hand, found in the Santee marls do not differ much as regards size from those of the sharks now living on the coast, and artesian wells in the phosphate region yield, at a depth of 700 feet below, these colossal teeth-teeth similar in size to the ancient

fossil teeth found far inland, imbedded in the Santee marls, and to those of the fish now living in the vicinity. As to the origin of the phosphate rock, the identity of the fossil shells it contains with those of the underlying marl make this much certain, that it consists of fragments broken from the irregular surface of the marl, and that its rounded and nodular form was imparted to it by the action of the waves and currents to which it was subsequently subjected. The important question of how a marl containing originally 60 per cent. of carbonate of lime and 2 to 4 per cent. of phosphate of lime has been changed into one containing 50 to 60 per cent. of phosphate of lime and 5 to 10 per cent. of carbonate of lime remains for consideration. It is a noteworthy circumstance, that, while the great body of the eocene marls in South Carolina have preserved their constitution almost unchanged, a remarkable change is manifest at the beginning and at the close of the series; in the buhr-stone on the northern border, and in the widely removed phosphate rock on the southern; in the buhr-stone the original carbonate of lime composing the shells has been replaced by silica, rendering great masses of rock, that once might have imparted valuable properties to the soils, valueless agriculturally; in the phosphate region masses of carbonate of lime have been converted into the phosphate, rendering them still more valuable to the tiller of the soil. Two theories have been offered to account for this substitution of the phosphate for the carbonate of lime.

One theory assumes that the fragments of marl were charged with the sweepings from guano beds formed above them by the congregation there, at some indefinite time in the past, of vast flocks of birds; in this case, bones of the birds should be among the fossils preserved in these beds. No such remains having been found, but instead the remains of numerous animals, such as the mastodon and elephant above mentioned, and it was thought that immense herds of these animals had collected at one time. about the shallow salt lakes in which the nodules were left upon the recession of the sea, just as animals now do about the salt licks of Kentucky, and that the phosphoric acid derived from their excrements and remains wrought the change in the marl. To this it is objected that the spots where the most of these bones are found are not the richest in phosphates; and while it is by no means probable that the nodules were in all, or even in most instances, formed where they are at present found, it is difficult to suppose that agencies of such local and restricted character as salt licks could account for the conversion of so great a mass of material, over an area so extensive, as that presented by the phosphate formation. The other explanation of the formation of these rocks is, that certain mollusks possess the power of separating the phosphate of lime from sea water, and that through their instrumentality the marl, and especially

the upper strata, became charged with a certain amount of phosphate of lime. That the proportion of the phosphate of lime thus obtained to the whole body of the superficial layers of the marl was afterwards increased ; 1st, by the removal of a considerable amount of the carbonate of lime, rendered soluble by the percolation through it of rain water containing carbonic acid, derived from the decomposing vegetable matters in the soil overlaying the marl. 2d, by a well known proneness of phosphoric acid, when diffusely distributed, to concentrate and to give rise to concretionary processes similar to those observed in the flint nodules and pebbles of the English chalk. This theory agrees with the diffused occurrence of phosphate of lime in the superficial layers of the marl, as well as with the fact that the upper layers of the deposits and the outside of the nodules are the richest in phosphate. It substitutes for a local cause a general one, commensurate at once with the wide area occupied by the phosphate rocks and by the phosphatic marls of the South Atlantic seaboard. Such a cause also might have been in operation ages ago, when the layers of phosphate rock, found at a depth of 300 feet in artesian borings, were forming; and it may be in operation now, as the dredging work of the United States Coast Survey shows that the marls accumulating at the depth of 200 fathoms on the floor of the Gulf Stream, between Florida and Cuba, contain a considerable percentage of phosphate of lime.

No systematic survey, determining the extent of these deposits, has yet been attempted. The only information on this head comes from prospectors, seeking easily accessible rock in localities convenient for shipment. Widely varying estimates as to the quantity of the rock have been ventured. Some have placed it as high as five hundred millions of tons, and others as low as five millions. The latter is the estimate of Prof. Shepard, who has prepared a map of the region. He traced the deposit over 240,000 acres, and roughly estimates the accessible rock as covering only about 10,000 acres. Even this estimated area at 800 tons per acre, which he gives as an average, should yield 8,000,000 tons. But if we examine a single mining region, as that for instance occupied by the Coo-aw company, we must conclude that he has very greatly underestimated the amount. This company has the exclusive right to a territory of about 6,000 acres in Coosaw river, besides the adjacent marshes, yet unexplored. Everywhere the river bottom is covered with rock, which for the most part forms a solid sheet, varying from 8 inches to 13 feet in thickness. Taking the lesser thickness, we have, with a specific gravity of 2.5, after subtracting 25 per cent. for loss in washing and drying, something over 1,700 tons to the acre, which would give for the river territory alone belonging to this one company something more than