The graduating class of Michigan University lias placed iD the campus, at Ann Arbor, an immense boulder. Dr. Win-chell, at the solicitation of the class, gave the following history of this gigantic " specimen :" THE BOULDER OF 1869. This stranger to our precincts, appropriated and adopted by the class of 1869, has traveled hither from the far north. It is probable its home, for many ages, was upon the northern shore of Lake Huron. There it was wrenched from its ancient fastenings by a geological convulsion, seized in the grip of the glacier, borne three hundred miles over obliterated river and lake, and relinquished, at last, within sight of the future temple of Western learning. Here it has lain for perhaps a hundred ages, awaiting the advent of the class of 1869, and its final installation in the University as voiceless lecturer on the history and mutations of the world. This traveled rock, to those who can enter into communion with it, recites a tale of varied adventure. It is a rock of much more than usual interest. It is a rock of rocks. It is not the stone of which the contemptuous could say," A stone's a stone and nothing more." It is an epitome of petrology; it is alithological museum ; it is a geological science converged to a focus ; it is a table of contents of the book of nature. Let us look into it. This interesting rock is a heterogeneous conglomerate, containing about seventeen cubic feet, and weighing, consequently, about three thousand pounds. Whatever angularities it possessed when first venturing from home, have all been worn off by contact with the world. On one side may be discovered not only the polish due to the action of the glacier, but also one or two distinct furrows scored into the flinty substance of the rock. The constituents of the conglomerate vary in size from grains of sand to fragments four or five inches in diameter. Most of these are themselves rounded and worn by some ancient conflict with geologic forces; but a few preserve still a rounded angularity. The constituent pebbles present a lively assortment of colors, from black to greenish blue, drab, rose-color, red, and white. The surface of the boulder intersects these various-colored pebbles without regard to hardness, quality, or complexion. It thus presents a diversity of colors worthy of some of the dashing patterns of modern calicoes. Indeed this rock, long familiar to all travelers over the " middle Ypsilanti road," has always been known as " the calico rock," and it is not impossible that this name gave it a charm in seniors' eyes. In studying carefully the composition of the boulder, I have recognized no less than twenty-one varieties of rocks and minerals: 1. Chlorite rock, a soft, homogeneous, blueish-green material, in fragments an inch or less in diameter; this is also called melaphyre by some writers. 2. Chlorite schist, in somewhat angular slaty fragments, on one side exposing a layer of about a square foot in extent. 3. Chloritic scales, or white crystalline chlorite. 4. Mica (muscovite) in scattered scales. 5. Argillite, of a reddish color, in limited amount. 6. Red jasper in small quantity. 7. Black jasper in smaller quantity. 8. Orthoclase in detached broken crystals, and as constituent of numerous pebbles. 9. Porphyrine, in numerous fragments of a homogeneous, reddish color. 10. Petrosilex, moderately abundant, and very hard. 11. Glassy quartz in detached fragments of the size of a marble and less. 12. Eose quartz. 13. Smoky quartz. 14. Silicious schist. 15. Granular Quartzite. 16. Quartzose grit. 17. Quartzose conglomerate. 18. Granulite, with abundant deep red orthoclase. 19. Granulite, with abundant pale red orthoclase—the last two and the Second named constituting half of the bulk of the boulder. 20. Gneiss, in limited amount. 21. Pyroxenic gneiss in greater abundance. The boulder illustrates, moreover, the phenomena of—1. Massive structure. 2. Schistose structure. 3. Gritty structure. 4. Pudding stone. 5. Semi-breccia. 6. Glacial polish. 7. Glacial grooves. 8. Glacial transportation. Here are not less than twenty-nine geological phenomena set forth by the teaching of a single stone. But this is not all. It is a revelator of unseen and impalpable facts. It speaks a history. In contemplating this lost rock we are led to think of the modern epoch, during which it has lain exposed upon the surface of the earth, beaten by a thousand wintery storms, the witness of the life and history of the savage tribes which pursued their game or fought theii battles among the hills and vales of the " beautiful peninsula." And then we think of the time when it was first transported to this region, and picture to ourselves the wrestling and the crashing of the great glacier along a journey of three hundred miles, and continued over a period of a thousand years or more. And next, we ask where the glacier picked it up, and under what circumstances it found our boulder existing. It may have wrenched it from a projecting crag ; it may have found it a fragment torn by an earthquake convulsion from its parent bed. But the parent bed, where was that ? What had been its history ? There was, and probably still remains, an extensive formation of rock, of which the glacier has brought us this specimen. There was an older time, then, when the powers of geology in their untamed energy were engaged in bringing together from twenty shores the materials which were to enter into the constitution of that formation. Who shall discover the shores whence they were gathered ? They are the ruins of a continent which nourished the growth even of the eozoic continent—the growth even of the germ of North America. Into the dim horizon of eternity sink the desolate undiscovered shores of that firstborn land. But it existed. Nor was that even the beginning. Imagination is called upon to take another flight into the retreating ages of terrestrial history. This granulite, this gneiss, this chloritic schist—these are themselves products of sedimentary deposition which went forward during an age anterior to the time when these rocks were bluff-bound shores yielding debris for our conglomerate. If the constituents of these were not themselves ground from some still more ancient beach, they show at least that old ocean existed, and was even then occupied in laying down courses of sediment —even of pure chemical precipitates—which were destined to be rewrought into rocks that should stand to the age of man. Perhaps the visible testimonies of our boulder go no further. But they have given thought an impulse which refuses to be arrested even at this limit. She demands what sort of a sea-bottom that primeval ocean rested upon. Was it also a bed of rock that had been accumulated in an ocean ? If so, upon what sort of a bottom did that older ocean rest 1 There must have been an ocean, in the history of the world, which rested on a floor of refrigerated lava. There must have been a, first ocean. To deny it is to deny that our globe has been in progress of cooling from a natural beginning. To deny it is to assume that its history began in the midst of an evolution that, under the laws of nature, is as likely to have had antecedent as subsequent terms. It is to deny that the earth has been cooling as long as physical laws render possible. It is to assume that it was created in mid career instead of at the commencement of it. Itis a suicide of the positive philosophy which makes the denial, since, by denying the existence of an antecedent molten condition of the globe the positivist postulates a creation at a point where creation was not necessary—obtrudes the ever incomprehensible miracle of creation at a juncture when he must perform another miracle by interrupting the spontaneous course of nature. So builds reason on the foundation stones bound up in this boulder. Even from this rock we mount into the past eternity, and grope for that beginning which was the source, the fountain—ieresMtli—whence flowed naturally the stream of events which we trace, by the lamp of science, down through the geologic ages, and witness, even to-day, rushing- like a mighty tide before our eyes, and bearing man himself along, with all his works, into the abyss of future years. And when thought reaches this limit she finds herself confronted by an adamantine wall. Beyond this is only Omnipotence ; and while the deep utterances of the soul of man speak ever of primary causation, reason discovers here that primary cause. This is the response of science to the intuitions of the soul. This is the triumph of the soul when science falls disabled. This is the harmony between nature and mind; this is the unison of philosophy and faith. Thanks, from the depths of the heart, that this ancient, war-worn boulder, smitten by the wandof science, has opened such a permanent fountain of God's eternal truth. The Fire Alarm for New York CUT. A new fire alarm for New York city is now in process of construction.the details of which are important as foreshadowing a general improvement in the methods now employed in giving notice of fires in most of the large cities in the United States. The system will differ in many respects from any system of fire alarm now in existence, but will combine all the best features of the telegraphic fire alarms now in use in other cities, the external apparatus to be made in a tasty and ornamental style. The Central Office of the new system will be established in the building known as Firemen's Hal], in Mercer St., and is to be provided with the following appliances: A sufficient number of self-acting, paper-registering apparatuses (with or without accompanying " relays," as may be deemed necessary), attached to the signal circuits, whereby alarms for fire received may be printed upon paper, to be detached and filed away for reference ; a test indicator for each circuit, whereby its general condition may be ascertained at any time, and, in addition, apparatus and appliances, to be on the principle of that used in testing the Atlantic Cable, enabling the operators to examine and test for faults, breakages, and the usual disturbances to which telegraph lines are subject; an "electro-magnetic watch clock," by means of which the tests made by the operators in charge, at stated intervals during the twenty-four hours, may be recorded; one or more alarm bells, so arranged that a break in the continuity of any of the several circuits shall be indicated, and notice given to the operator ; an apparatus for automatically sending out to the various alarm stations the signal number which may be required, and so arranged that, being capable of being set to any number, from 1 to 999, when thus set and started into action, its circuit wheel, set to the required number or alarm, acts by proper appliances, so that the alarm is sent out on each circuit successively, and with equal and great force, and in so rapid a manner that the entire number of alarm stations shall receive one blow on the gong within one and one half seconds, although the force of the battery is thrown on only ten circuits at one time. One such apparatus shall also be attached to the " signal station " circuits, and in like manner as above, the " alarm " shall be tapped on each or all the signal boxes ; also,one or more switch-boards,with sufficient switches, circuit-breaking keys, and other appliances as shall permit alarms being sont on one or more of the several circuits as may be desired. All of the machines and other attachments and appli-pliances are to be of the finest workmanship, elaborately finished and mounted, and so designated in all their multitucin-ous functions that the operator in charge shall be able to handle them with celerity, and have the fullest and most complete command over all the circuits at all times. Communication with, the central office of the Police telegraph will be established by means of improved " dial machines," so arranged as to be capable of expressing in a comprehensive and rapid manner the peculiar style of message relating to fires, which are usually forwarded to and from that office. The chief innovation of the new system, and the one in which a belief in its usefulness is mainly placed, is in the alarm stations scattered throughout the city, but conforming as nearly as possible to the code of signal stations now in use. The stations will be placed nearer together in the upper part of the city, and the time to be gained in giving notices Df fires is to be found in the fact, that from each one of these 3tations an alarm can be given, which is not now the case. At each of these stations is to be placed a mechanical gong ringer, so constructed that the power of a single cup of small capacity shall start the machinery, which strikes a gong or bell of about twenty pounds weight, and the machine is con-Jtructed to work upon either an open or closed circuit. The machine, with the weight, will be inclosed in a black walnut Jase with glass front—the door having a good brass tumbler lock and one key—and securely fastened to the wall of the station in such part of the building as may be indicated. The The case is so constructed that the weight can be wound up without the case being opened, and an indication given when the weight is run down. Each is supplied with a good lightning arrester, and a telegraph key, and the wires, leading from the poles to and from these machines will be suitably insulated and properly protected. Each " street box " will be constructed of iron, roof-shaped, with an outer and an inner case, containing an automatic signal machine, which is wound up and started into operation by pulling a button or similar device ; the door of the outer case to be opened to obtain access to the button. The inner case is to contain the automatic machine—itself securely incased in an iron box—which is to have its circuit-wheel cut corresponding to the station number, and must be capable of Signaling that number with perfect exactness and uniformity; the machines on each circuit to be so speeded as to give a slightly different rate of signal, so that when two or more signals are to be received at the Central Office.they may be readily distinguished. This machine is to be of the finest constrnc-tion.and capable of running with a one-ounce weight attached to the handle. The inner case is also to contain a bell magnet, or electric alarm bell, which will sound sufficiently loud to be heard ten feet from the boxes when closed, a signaling key, and a good lightning arrester. The outer door is to be provided with a strong brass tumbler lock, with five keys. The inner door, to which is attached the button or device for starting the machinery,will also be provided with a strong brass tumbler lock and one key. All the locks of the outer cases are to be uniform in style and wards. The keys of tlicsa boxes are to be in the charge of the policemen and firemen, except one for each box, which is to be left at a place to tic stated by a plate on the box itself, so that it can be accessible at all hours to any person discovering a fire. The boxes are to be placed, whenever practicable, in such public places as hotels and drug stores, which ar open all the time, and arr uniformly to be made long and narrow, so that they will not be cumbersome when placed upon the telegraph poles, as in many parts of the city they must be. Bubbles of Mercury Floating on "Water, When the lecture room of a chemical laboratory is provided with a sufficient supply of water under strong pressure, it is possible to make, and .exhibit there an experiment, which, owing to a deficient pressure of water in such rooms, has been almost unnoticed. The experiment is the following: Under an ordinary water tap, the opening of which has from 10 to 12 m. m. diameter, a large sized porcelain basin is placed, containing from 15 to 20 kilos, of mercury ; the water tap being suddenly opened, a strong flow of water is caused to fall into the basin at a hight of from 8 to 10 centimeters from its tot-tom. On turning off the flow of water again, it will be seen that on the surface of that fluid there float about bubbles of mercury, usually exhibiting a diameter of only one centimeter, but occasionallysome are found of two or three times that size. As a rule these bubbles are very ephemeral ; now and then, however, it happens that some may be caught, along with a quantity of water, in a small beaker glass, and, on the mercurial bubbles bursting, it will be seen how very sm all a quantity of mercury these bubbles consist of. Professor Hof-mann mentions that he saw this experiment first exhibited in the lecture room of the Royal College of Chemistry, London, when, some twenty years ago, Professor Melsens, from Brux-elles, was on a visit there. The pressure of water at the lecture room just named is from 10 to 12 meters; in the now laboratory of Berlin University the pressure of the water cir culating in the tubes and pipes is from 20 to 25 meters. A New Pyrometer, Everybody knows the difficulties which stand in the way of exactly estimating high temperatures. The best pyrometers we have had hitherto can only be supposed to give approximate results, and some of them may be very wide of the truth. It is now announced that M. Lamy has devised an instrument which shows within two or three degrees Centigrade the temperature of a furnace heated up to redness, and gives its indication at a distance from the furnace, so that at a porcelain factory, for example, a manager can sit in his office and see the temperatures of all the furnaces in his establishment. The instrument is as simple as it seems to be efficient. It is merely an iron retort, containing marble, the neck of which communicates, by means of a narrow tube, with a needle moving over a dial plate. As the heat rises, the marble is decomposed, and carbonic acid set at liberty. A special contrivance measures the tension the gas arrives at, and as this has a direct relation to the temperature, the measure of the one is made the measure of the other. Up to a certain point, we have little doubt this instrument may be relied upon. The Reef-building Corals. The variety of compact and branching corals far exceeds description : 120 species are inhabitants of the Red Sea alone, and an enormous area of the tropical Pacific is everywhere crowded with the stupendous works of these minute agents, destined to change the present geological features of the globe, :: s their predecessors have done in the remote ages of its existence. Four distinctly different formations are due to the coral-building polypes in the Pacific and Indian Oceans : namely, lagoon islands or atolls, encircling reefs, barrier reefs, and coral fringes, all nearly confined to the torrid zone. An atoll is a ring or chaplet of coral, inclosing a lagoon, or portion oi the ocean, in its center. The average breadth of that part of the ring which rises above the surface of the sea is about a quarter of a mile, often less, and it is seldom more than from six to ten or twelve feet above the waves ; hence the lagoon islands are not visible, even at a very small distance, unless when they are covered by the cocoanut palm, or the pandanus, which is frequently the case. On the outside, the ring or circlet shelves down for a distance of one or two hundred yards from its edge, so that the sea gradually deepens to about twenty-five fathoms, beyond which the sides of the ring plunge at once into the unfathomable depths of the ocean, with a more rapid descent than the cone of any volcano. Even at the small distance of some hundred yards, no bottom has been reached with a sounding line a mile and a half long. All the coral in the exterior of the ring, to a moderate depth below the surface of the water, is alive ; all above it is dead, being the detritus of the living part, washed up by the surf, which is so heavy on the windward side of the tropical islands of the Pacific and Indian Oceans, that it is often heard miles off, and is frequently the first warning to seamen of their approach to an atoll. The outer margins of the Maldive atolls, consisting chiefly of millepores and porites, are beat by a surf so tremendous that even ships have been thrown by a single heave of the sea, high and dry on the reef. The waves givj innate vigor to the polypes by-bringing an ever-renewed supply of food to nourish them, and oxygen to aerate their juices; besides, uncommon energy is given and maintained by the heat of a tropical sun, which gives them power to abstract enormous quantities of solid matter from the water to build their stony homes, a power that is efficient in proportion to the energy of the breakers which furnish the supply. On the margin of the atolls, close within the line where the coral is washed by the tide, three species of nullipores flourish ; they are beautiful little plants, very common in the coral islands. One species grows in thin spreading sheets, like a lichen ; the second in strong knobs as thick as a man's finger,radiating from a common center; and the third species, which has the color of peach blossom, is a reticulated mass of stiff branches about the thickness of a crow's quill. The thi.:e species either grow mixed or separately, and although they can exist above the line of the corals, they require to be bathed the greater part of each tide ; hence, a layer two or three feet thick, and about twenty yards broad, formed by the growth of the nullipores, fringes the circlet of the atolls and protect the coral below. The lagoon in the center of these islands is supplied with water from the exterior, by openings in the lee side of the ring, but as the water has been deprived of the greater part of its nutritious particles and inorganic matter by the corals on the outside, the hardier kinds are no longer produced, and species of more delicate forms take their place. The depth of the lagoon varies from fifty to twenty fathoms or less, the bottom being partly detritus, and partly live coral. In these calm, limpid waters the corals are of the most varied and delicate structures, of the most charming and dazzling hues. When the shade of evening comes on, the lagoon shines like the Milky Way, with myriads of brilliant sparks. The microscopic medusae and crustaceans, invisible by day, form the beauty of the night, and the sea-feather, vermilion in daylight, now waves with green, phosphorescent light. This gorgeous character of the sea-bed is not peculiar to the lagoons of the atolls; it prevails in shallow water throughout the whole coral-bearing regions of the Pacific and Indian Oceans. Encircling reefs differ in no respect from the atoll ring, except in having islands in their lagoons, surrounded also by coral reefs. Barrier reefs are of the same structure as the atoll rings, from which they only differ in their position with regard to land Thoy form extensive lines along the coasts, from which they are separated by a channel of the sea of variable depth and breadth, sometimes large enough for ships to pass. A very long one runs parallel to the west coast of New Caledonia, and stretches for 120 miles beyond the extremity of the island. But a barrier reef off the northeastern coast of the Australian Continent is the grandest coral formation existing. Rising at once from an unfathomable depth of ocean,it extends for 1000 miles along the coast,with a breadth varying from 200 yards to a mile, End at an average distance of from SO to 60 or 70 miles from the coast, the depth of the channel being from 10 to 60 fathoms. The pulse of the ocean, transcendently sublime, beats perpetually in peals of thunder along that stupendous reef, the fabric of almost microscopic beings.—Mrs. SomermUe. An Old Map of Pittsburgh. By the kindness of Mr. A. T. Haumann, Civil and Mining Engineer, of Pittsburgh Pa., we are in receipt of a map of Pittsburgh as it was in 1795. It is a very interesting document, and shows the exact position of the fortifications and barracks, of historical importance in connection with the early frontier wars of this country. The years which have since elapsed have made immense changes in the appearance of the town. At the period mentioned the fky was occasionally clouded by the smoke of artillery ; now it is almost constantly veiled by the smoke of its manufactories, and its atmosphere resounds with the din of giant industries. Mr. Haumann will please accept our thanks. The map is photographed, and we presume may be obtained on application to Mr. Haumann at 130 Smithfield street, Pittsburgh, Pa.