of animal life. Here is a specimen not much more than twice as large as a man's hand, that has representatives from three of the grand divisions of the animal kingdom. This central figure is a fine large Trilobite, a beautiful specimen of the Articulata; and here are several fragments of coral and the stem of an Encrinite from the Radiata, while the Molusca is represented by several of the Acephala and a Gasterapod. There are great numbers of Arthocerata found in this rock. Some of them are of very great size. I have seen sections of them that were eight inches in diameter. I have a part of one in my collection which is not more than six inches in diameter at its largest part, that is eight feet in length. Ammonites of considerable size are found in this rock. Among the Acephala are several species of Septæna. Strophomena, Orthis, etc., are common in some of the layers of this rock.

This rock is somewhat extensively used for building material, although for that purpose it is not equal in value to the magnesian beds below it. It makes excellent lime, and is extensively used for that purpose. Some of the layers of this rock, in this locality, are made up almost exclusively of fossil shells and corals, and are very compact and fine-grained, and receive an excellent polish, making a very beautiful figured marble. The Trenton Limestone is found principally in the bend of the river, in the upper part of Lee county, extending about four miles south, and is also found in a narrow belt on the north-west side of the river, extending from Pine creek, in Ogle county, to within a mile of Dixon.

GALENA LIMESTONE.

The Galena Limestone succeeds and rests upon the Trenton Limestone. The line of demarkation between this and the Trenton Limestone is not always easily ascertained. Layers, partaking sometimes more of the characteristics of one of these formations and then the other, are often found intermingled for some distance, although the characteristics of the mass of the two formations are very distinct. It appears to be the prevailing rock, underlying the surface of the elevated prairie, over a considerable portion of the north-western part of the State-the streams having in many places cut down through it into the strata beneath. The Galena Limestone is a rock peculiar to the West, and is a very important member of the lower Silurian series. It is important not only from its thickness and the extent of country which it covers, and the many economical uses made of the rock itself, but from the rich minerals it contains. It being peculiarly the lead-bearing rock of the North-West, as is indicated by its name.

The Galena Limestone is a coarse-grained, porous, and sometimes friable rock. It has a dull grayish and sometimes yellowish color, and, from its porous character, weathers out very rough and irregularly. It is everywhere characterized by its peculiar fossil, the Sun Flower Coral, the Coscinapora sulcata or recepticalites of Hall. In the lower beds of this rock there is a very beautiful species of

Favosite quite common. Its pentagonal columns, or rather tubes, filled with transverse lamina of a pure siliceous material, radiating from a point, present a very beautiful appearance, particularly on a recent fracture. This coral is often found in large masses where it has weathered out of the rock, sometimes entire, but more frequently broken into fragments. Among the gasteropods found in this rock are the Marchisonia, Pleurotomaria, etc. The Orthoceras, Crytoceras, Ammonite, and some of the bivalves common to the Trenton Limestone, are often found in the lower beds of this rock. This limestone is the prevailing rock along the river, from a mile above Dixon to near Sterling, where it disappears beneath the Hudson River group and the Niagara Limestone. This rock, as may be seen by the map, spreads out over a much greater extent of country as we go back from the river, on either side.

HUDSON RIVER GROUP.

On the immediate banks of the river, along the rapids at Sterling, and at the base of the bluffs a mile above town, on the north side of the river, may be seen the various rocks, shales, clayey and bituminous deposits described by Professor Hall as the Hudson River Group. The rapids in Rock River at Sterling seem to have been produced by the wearing away of the shales of this formation. I have been unable to ascertain what the exact thickness of this group may be, but think that it is probably not more than twenty-five or thirty feet. On the map accompanying this paper I have represented this formation in a narrow belt, surrounding the Niagara Limestone, on the east and north side.

Although the rocks of this formation do not appear at the surface, except at the rapids and at the bluff above Sterling, I have been able to trace them, in the course indicated on the map, by examination of the rocks thrown up in the digging of wells.

NIAGARA LIMESTONE.

The Niagara Limestone is found on the north side of the river, above Sterling, extending through the north-eastern part of Whiteside county. This rock is also a magnesian limestone, and resembles, in its composition and appearance, the Galena Limestone. There is a good opportunity to examine this formation at the quarries, a mile above Sterling. There it may be seen resting on a green compact rock of the Hudson River Group. The lines of charts common to this rock are found there in abundance, sometimes forming layers six inches thick. The characteristic fossil of this rock, the Catenapora Escharoides, and a beautiful species of Favosite, are common there. I also noticed a species of Marchisonia and two or three bivalves. The rock from these quarries makes an excellent building stone, and is extensively used for that purpose.

MASTODON GIGANTEUS.

By C. D. WILBER.

During the last ten years, in various portions of Illinois, have been found the teeth and tusks, and, in some instances, the vertebræ, of a huge mammal, called the Mastodon. All the remains, thus far discovered, are indicative of the same species, i. e., Giganteus-so called from its vast size. Many teeth have been found in Northern Illinois, especially in the Lead regions. Some have been washed out by the rivers, at Spring flood, while others have been obtained in railway sections.

The "largest specimen" of this order, (Mastodon,) once lived near Aurora, where his remains were recently found, in excavating for the track of the Chicago, Burlington and Quincy Railroad. There were the tusks and seven teeth-all in a good state of preservation, "the tooth of time" having consumed all other vestiges. The teeth and tusks were found as near each other as when they were in the animal's head; from which we may conclude that he laid him down to die with much composure, and was allowed to sleep on quietly through the ages.

The tusks, when entire, measured ten feet in length and ten inches in diameter at the base; they were curved upward, and were considerably worn at the ends, on the under side. They appear to have been used as huge levers, for the purpose of overturning trees, large and small, whose foliage and branches served him for food -a conclusion at which we also arrive from the construction of his teeth.

The foregoing figure represents one of the tusks in the natural position. As it was uncovered, one of the laborers, an Irishman, with an ax, cut it nearly asunder, thinking it was "white wood." It resembles the tusk of the Elephant, (or Mammoth, which is simply a fossil elephant,) whose tusks are fixed to the upper jaw like incisor teeth, and have a solid structure. The tusk of the Mastodon has an outer shell, one inch in thickness, very hard, fibrous and compact, not unlike the massive curved cables stretched over the towers at the Niagara suspension bridge. The mass within is white, like decayed ivory. The weight of each tusk is 200 pounds, and judging from its shape, position and material, we are obliged to say that a forest of oak or pine would "grow small by degrees" before a drove of these formidable tree-eaters.

The teeth, as one would suppose, are of great size, and weigh from five to eight pounds each. The front teeth weigh from three to five pounds, and resemble, in their construction, those of graminivorous animals. They appear to have been worn out, the crown or enamel of the teeth having nearly disappeared.

The above cut represents a "wisdom tooth" of the Mastodon. It weighs seven pounds, and measures eight inches in length and breadth, and is about five inches in thickness. The protuberances of the surface, from which the name Mastodon is derived, are smooth, and seem to have been used for breaking portions of limbs of trees, which was done after the manner of an old fogy flaxbreak, the processes shutting into, but not touching each other. The pieces or chips thus made, were then masticated by the front teeth, which served as molars, an exception to the present mode of grinding. However, some contend that the front teeth were used only as nippers, for biting off branches or leaves and grass.

By observing the last figure, which represents one of the smaller teeth, the relation of the two sets will be readily perceived, and it will also appear that the huge monster was decidedly a vegetarian.

"The teeth consist chiefly of dentine, invested by enamel, though a layer of cement, thinner than in the Elephant, invests the fangs, and is spread over the crown. The whole number of teeth is twenty-four, of which rarely more than eight are in use at one time. They are developed from behind, forward, in order to relieve the jaws from the excessive weight of the whole at once. Two on each side, in each jaw, are developed soon after birth, and are shed early. The first and second of the upper jaw resemble those of the lower. The third is three-ridged. The fourth is threeridged, larger, with the eminences notched. The fifth has three ridges, each with two eminences. The sixth is four-ridged, with a small heel; the points sometimes bifurcated, deep furrowed, and measuring six and one-fourth by three inches; and in one instance, nine and a half to five and a half inches."

Several years ago, six Mastodons were exhumed in New Jersey; and, as Cuvier had predicted from a single tooth, they had twenty ribs, like the Elephant. Within the ribs of one of the Mastodons, a dark colored earth was found, which, on being examined with a microscope, exhibited the remains of some vegetable, which Dr. Lyell considers to have been the half decayed twigs and leaves of the pine or fir tree. The whole mass of vegetable remains taken from one carcass was eight bushels, or one stomachful!!!

Taking the tusk as one-third of the length, which is the usual estimate, and allowing half the length for the height of the animal, we can easily restore the proportions of the Mastodon, and we are obliged, therefore, to conclude that when alive and in all his glory, he was thirty feet long and fifteen feet high. But this estimate need not transcend belief, for we have already, in several museums of Natural History, remains of the Megatherium, (great beast,) measuring twenty-four feet in length. This was also a grass-eating animal. The Zeuglodon, (yoked tooth,) whose remains are in the St. Louis Museum, (Wyman's,) was ninety feet in length. It be