of the toad and frog-this extinct animal is supposed to have been a huge frog. It has more recently received the name of labyrinthodon, from the peculiar structure of its teeth, which, under the microscope, present a series of irregular folds, resembling the labyrinthic windings. of the human brain. The pictorial representation in the following chapter is from a model at the London Crystal Palace. Later a variety of tracks, referred to the chirotherium, tortoises, and reptiles were discovered in the new red sandstone in the neighborhood of Liverpool. The largest footprint was nine inches long, and six inches broad, the length of the step approaching to two feet. Abundant footprints along with ripple marks, have been found on layers of the forest marble, to the north of Bath. A communication to the Journal of Science, in 1836, by President Hitchcock, of Amherst College, called attention to some very distinct tracks in the red sandstone of the Connecticut valley, resembling the impressions left on the muddy banks of the river by the aquatic birds now common to the locality.

Marks of Rain Drops in Solid Rocks.

Similar impressions of rain drops occur in the Storeton quarries, where tracks of the chirotherium are found. The under surface of the strata, at the depth of thirty-two or thirty-five feet, presents a remarkably blistered or watery appearance, being densely covered by minute hemispheres of the same substance as the sandstone. The impressions are sometimes perfect hemispheres, indicating a vertical fall of rain; but in other cases they are irregular and elongated in a particular direction, as if the drops had struck the surface obliquely, indicating a wind accompanying the rain. President Hitchcock mentions specimens of sandstone in his possession, obtained from various parts of the United States, which show footprints, ripple marks and rain drops, the latter evincing, by a uniform elongation of shape, the direction of the wind. when the rain fell.

Walking along our shores in the present day, we observe a welldefined cast of our own footstep left in the sand still wet from the retreating tide, and similar distinct impressions made by the passage of animals and birds across it, and by the descent of a shower of rain upon it. In the same manner it is probable that the tracks which the new red sandstone presents were formed on the shores of an estuary, or a tidal river, between high and low water mark-then dried and hardened by the action of the sun and air during the subsiding of the watersthe returning waves washing up mud to cover up the impressions, the two layers uniting, to exhibit, if ever separated, the one a mould, and

the other a cast from it, of the forms that have been there. The observation of like phenomena, now, to these unfolded by this geological formation, are of no mean importance and interest to mankind, in every condition of society. Many a depredator has been detected by the correspondence of his foot to its imprint in the snow or loose earth near the place of his crime. The North American Indian finds hi; enemy by his trail, and can not only distinguish between the elk and the buffalo by the marks of their hoofs, but determine with great exactness the space of time that has elapsed since the animals have passed. In the deserts of Africa, the track of the camels proclaims to the Arab whether a heavily or lightly laden caravan has crossed the sands. But

from the imprints presented by the sandstone formation, we gather information respecting what transpired many thousands of years ago, catch a glimpse of the gigantic birds and strangely formed quadrupeds that then existed, and even have indicated to us, in a manner so plain as not to be mistaken, the direction from which the wind blew while a shower of rain was falling.

We find embedded in the earth the fossil remains of vast quantities

of animals no less remarkable for their minuteness and construction than those already described in the preceding pages are for their colossal size. They are called animalcules, or infusoria. Their skeletons constitute nearly the whole mass of some soils and rocks, many feet in thickness, and extending over areas of several miles. Such is the polishing slate, in Bohemia, which occupies a surface of great extent, probably the site of an ancient lake, and forms slaty strata of fourteen feet in thickness, almost wholly composed of the shields of animalcules. The size of a single one, forming the polishing slate, amounts upon an average, and in the greatest part, to one-sixth of the thickness of a human hair. Such is the statement of

Ehrenberg, which naturally suggests the reflection of the French philosopher, that if the Almighty is great in great things, he is still more so in those which are minute; and furnishes additional data for the well known moral argument of the theologian, derived from a comparison of the telescope and the microscope: The one led me to see a system in every star; the other leads me to see a world in every atom. The one taught me that this mighty globe, with the whole burden of its people and of its countries, is but a grain of sand on the high field of immensity; the other teaches me that every grain of sand may harbor within it the tribes and the families of a busy population. The one told me of the insignificance of the world I tread upon; the other redeems it from all insignificance -for it tells me that in the leaves of every forest and in the flowers of every garden, and in the waters of every

rivulet, there are

worlds teeming with life, and numberless as

the stars above.

The composition of the polishing slate of Bohemia is far from being unique; for in several other European localities, and very largely in America, strata consisting mainly of fossil animalcules have been observed. This is the case with the infusorial earth of Virginia, a yellowish clay, forming a deposit from twelve to fifteen feet in thickness, upon which the towns of Richmond and Petersburg are built. The surface of the country over which it extends is characterized by a scanty vegetation, owing to the nature of the soil dependent on the minute organisms of which it almost entirely consists. When a few grains of this earth are properly prepared for microscopic examination, immense numbers of the shields or

cases of animalcules are visible under a magnifying power of three hundred diameters; in fact, the merest stain left by the evaporation of water in which some of the marl has been mixed, teems with these fossil remains. The farther we pursue our investigations in this direction, the more wonderful do the discoveries become.

These organisms are of exquisite structure and comprise many species and genera. The most beautiful and abundant are the circular shields, which are elegant saucer-shaped cases, elaborately ornamented with openings disposed in curves, somewhat resembling the machine-turned sculpturing of a watch. These shells are from one-hundredth to one-thousandth of an inch in diameter. The body of the living animalcule was protected and enclosed by a pair of these concave shells.

The Smallest Creatures ever Discovered.

Beds of infusorial earth occur in almost every quarter of the globe. A large proportion of the sand of the Libyan desert consists of microscopic fossil remains; and the marine sands of the Paris basin are in some localities so full of microscopic forms, that it is calculated that a cubic inch of the mass contains sixty thousand. Many of the peat bogs of Ireland contain layers of a white, earthy substance, which, when dry, is of the appearance and consistence of brittle chalk, and this consists of the cases of animalcules.

Infusoria abound also at the present time. They are generally to be found in stagnant pools, and not unfrequently in springs, rivers, lakes and seas; also in the internal moisture of living plants and animal bodies, and are probably at times carried about in the vapor and dust of the atmosphere. Unlike the larger animals, throughout the whole of which we can trace one common type, the forms of these minute creatures are varied and singular. Some are egg-shaped, others resemble spheres; others again different kinds of fruit, funnels, tops, cylinders, pitchers, wheels, flasks, eels, serpents and many classes of animals with jointed skeletons.

Some of the animalcules are visible to the naked eye, as moving points though the smallest are not more than the 24,000th of an inch in diameter, a single drop of water having been estimated to contain many thousands of them. They were formerly supposed to be little more than mere particles of matter endowed with vitality; but Ehrenberg has discovered in them an apparatus of muscles, intestines, teeth, different kinds of glands, eyes, nerves, and organs of reproduction. They not only propagate by eggs, but by self-division; and are the most reproductive of all organized bodies. They possess a comparatively long life, and in general main

tain themselves pretty uniformly against all external influence, as do larger animals. As far as is yet known, they appear to be sleepless.

It cannot but be a matter of great interest to learn, if possible, the use of these minute animals in the economy of nature. That they are not merely accidents in creation we may be quite certain, and that they simply enjoy life and do not contribute to the well-being of the whole, may be considered equally improbable, and too unlike the ordinary course of

A DROP OF WATER AS SEEN UNDER THE MICROSCOPE.

nature to be admitted for a moment. All things work together, and we may in all cases, safely inquire concerning the adaptation of any group, however minute or apparently unimportant it may at first appear.

It has been ingeniously suggested by Professor Owen that these little creatures are the appointed devourers of organic matter immediately before its final decomposition into inorganic elements. For, consider, says he, their incredible numbers, their universal distribution, their insatiable.