vast lapse of time consumed in their growth, the elements were gnawing, carving and channeling the surface, and the outcropping edges of the formations were becoming more and more jagged, and now, after the last stratum had been added, and the whole had been lifted from the waters that gave it birth, there ensued perhaps a still vaster era, during which the history was simply that of surface erosion. The face of the state became creased with the wrinkles of age. The edges of her rocky wrappings became ragged with the wear of time. The remaining Devonian periods, the great Carboniferous age, the Mesozoic era, and the earlier Tertiary periods passed, leaving no other record than that of denudation.

THE GLACIAL PERIOD.

With the approach of the great Ice Age, a new chapter was opened. An immense sheet of ice moved slowly, but irresistibly, down from the north, planing down the prominences, filling up the valleys, polishing and grooving the strata, and heaping up its rubbish of sand, gravel, clay and bowlders over the face of the country. It engraved the lines of its progress on the rocks, and, by reading these, we learn that one prodigious tongue of ice plowed along the bed of Lake Michigan, and a smaller one pushed through the valley of Green bay and Rock river, while another immense ice-stream flowed southwestward through the trough of Lake Superior and onward into Minnesota. The diversion of the glacier through these great channels seems to have left the southwestern portion of the state intact, and over it we find no drift accumulations. With the approach of a warmer climate, the ice-streams were melted backward, leaving their debris heaped promiscuously over the surface, giving it a new configuration. In the midst of this retreat, a series of halts and advances seem to have taken place in close succession, by which the drift was pushed up into ridges and hills along the foot of the ice, after which a more rapid retreat ensued. The effect of this action was to produce that remarkable chain of drift hills and ridges, known as the Kettle range, which we have already described as winding over the surface of the state in a very peculiar manner. It is a great historic rampart, recording the position of the edge of the glacier at a certain stage of its retreat, and doubtless at the same time noting a great climatic or dynamic change.

The melting of the glacier gave rise to large quantities of water, and hence to numerous torrents, as well as lakes. There occurred about this time a depression of the land to the northward, which was perhaps the cause, in part or in whole, of the retreat of the ice. This gave origin to the great lakes. The waters advanced somewhat upon the land and deposited the red clay that borders Lakes Michigan and Superior and occupies the Green bay valley as far up as the vicinity of Fond du Lac. After several oscillations, the lakes settled down into their present positions. Wherever the glacier plowed over the land, it left an irregular sheet of commingled clay, sand, gravel and bowlders spread unevenly over the surface. The depressions formed by its irregularities soon filled with water and gave origin to numerous lakelets. Probably not one of the thousands of Wisconsin lakes had an existence before the glacial period. Wherever the great lakes advanced upon the land, they leveled its surface and left their record in lacustine clays and sandy beach lines.

With the retreat of the glacier, vegetation covered the surface, and by its aid and the action of the elements our fertile drift soils, among the last and best of Wisconsin's formations, were produced. And the work still goes on

CLIMATOLOGY OF WISCONSIN.

BY PROF. H. H. OLDENHAGE.

The climate of a country, or that peculiar state of the atmosphere in regard to heat and moisture which prevails in any given place, and which directly affects the growth of plants and animals, is determined by the following causes: Ist. Distance from the equator. 2d. Distance from the sea. 3d. Height above the sea. 4th. Prevailing winds; and 5th. Local influences, such as soil, vegetation, and proximity to lakes and mountains.

Of these causes, the first, distance from the equator, is by far the most important. The warmest climates are necessarily those of tropical regions where the sun's rays are vertical. But in proceeding from the equator toward the poles, less and less heat continues to be received by the same extent of surface, because the rays fall more and more obliquely, and the same amount of heat-rays therefore spread over an increasing breadth of surface; while, however, with the increase of obliquity, more and more heat is absorbed by the atmosphere, as the amount of air to be penetrated is greater. If the earth's surface were either wholly land or water, and its atmosphere motionless, the gradations of climate would run parallel with the latitudes from the equator to the poles. But owing to the irregular distribution of land and water, and the prevailing winds, such an arrangement is impossible, and the determination of the real climate of a given region, and its causes, is one of the most difficult problems of science.

On the second of these causes, distance from the sea, depends the difference between oceanic and continental climates. Water is more slowly heated and cooled than land; the climates of the sea and the adjacent land are therefore much more equable and moist than those of the interior.

A decrease of temperature is noticeable in ascending high mountains. The rate at which the temperature falls with the height above the sea is a very variable quantity, and is influenced by a variety of causes, such as latitude, situation, moisture, or dryness, hour of the day and season of the year. As a rough approximation, however, the fall of 1° of the thermometer for every 300 feet is usually adopted.

Air in contact with any part of the earth's surface, tends to acquire the temperature of that surface. Hence, winds from the north are cold; those from the south are warm. Winds from the sea are moist, and winds from the land are usually dry. Prevailing winds are the result of the relative distribution of atmospheric pressure blowing from places where the pressure is highest, toward places where it is lowest. As climate practically depends on the temperature and moisture of the air, and as these again depend on the prevailing winds which come charged with the temperature and moisture of the regions they have traversed, it is evident that charts showing the mean pressure of the atmosphere give us the key to the climates of the different regions of the world. The effect of prevailing winds is seen in the moist and equable climate of Western Europe, especially Great Britain, owing to the warm and moist southwest winds; and in the extremes of the eastern part of North America, due to the warm and moist winds prevailing in summer and the Arctic blasts of winter.

Among local influences which modify climate, the nature of the soil is one of the most important. As water absorbs much heat, wet, marshy ground usually lowers the mean temperature. A sandy waste presents the greatest extremes. The extremes of temperature are also modified by extensive forests, which prevent the soil from being as much warmed and cooled as it would be if bare. Evaporation goes on more slowly under the trees, since the soil is screened from the sun. And as the air among the trees is little agitated by the wind, the vapor is left to accumulate, and hence the humidity of the air is increased. Climate is modified in a similar manner by lakes and other large surfaces of water. During summer the water cools the air and reduces the temperature of the locality. In winter, on the other hand, the opposite effect is produced. The surface water which is cooled sinks to lower levels; the warmer water rising to the surface, radiates heat into the air and thus raises the temperature of the neighboring region. This influence is well illustrated, on a great scale, in our own state by Lake Michigan.

It is, lastly, of importance whether a given tract of country is diversified by hills, valleys and mountains. Winds with their warm vapor strike the sides of mountains and are forced up into higher levels of the atmosphere, where the vapor is condensed into clouds. Air coming in contact, during the night or in winter, with the cooled declivities of hills and rising grounds becomes cooled and consequently denser and sinks to the low-lying grounds, displacing the warmer and lighter air. Hence, frosts often occur at these places, when no trace of them can be found at higher levels. For the same reason the cold of winter is generally more intense in ravines and valleys than on hill tops and high grounds, the valleys being a receptacle for the cold-air currents which descend from all sides. These currents give rise to gusts and blasts of cold wind, which are simply the out-rush of cold air from such basins. This is a subject of great practical importance to fruit-growers.

In order to understand the principal features of the climate of Wisconsin, and the conditions on which these depend, it is necessary to consider the general climatology of the eastern United States. The chief characteristic of this area as a whole is, that it is subject to great extremes-to all those variations of temperature which prevail from the tropical to the Arctic regions. This is principally due to the topographical conditions of our continent. The Rocky mountains condensing the moisture of the warm winds from the Pacific and preventing them from reaching far inland, separate the climate of the Mississippi valley widely from that of the Pacific slope. Between the Gulf of Mexico and the Arctic sea there is no elevation to exceed 2,000 feet to arrest the flow of the hot southerly winds of summer, or the cold northerly winds of winter. From this results a variation of temperature hardly equaled in any part of the world.

In determining the climates of the United States, western Europe is usually taken as the basis of comparison. The contrast between these regions is indeed very great. New York is in the same latitude with Madrid, Naples and Constantinople. Quebec is not so far north as Paris. London and Labrador are equi-distant from the equator; but while England, with her mild, moist climate, produces an abundance of vegetation, in Labrador all cultivation ceases. In the latitude of Stockholm and St. Petersburg, at the 60th parallel, we find in eastern North America vast icefields which seldom melt. The moist and equable climate of western Europe in high latitudes is due to the Gulf Stream and the southwest winds of the Atlantic, which spread their warmth and moisture over the western coast. Comparison, however, shows that the climate of the Pacific coast of North America is quite as mild as that of western Europe; and this is due to the same kind of influences, namely, to the warm, moist winds and the currents of the Pacific. And to coptinue the comparison. still further, in proceeding on both continents from west to east, or from ocean into the interior, we find a general resemblance of climatic conditions, modified greatly, it is true, by local influences.

The extreme summer climate of the eastern United States is owing to the southerly and southwesterly winds, which blow with great regularity during this season, and, after traversing great areas of tropical seas, bear the warmth and moisture of these seas far inland, and give this region the peculiar semi-tropical character of its summers. The average temperature of summer varies between 80° for the Gulf states, and 60° for the extreme north. While in the Gulf states the thermometer often rises to 100°, in the latitude of Wisconsin this occurs very seldom. During winter the prevailing winds are from the northwest. These cold blasts from the Arctic sea are deflected by the Rocky mountains, sweep down unopposed into lower latitudes, and produce all the rigors of an arctic winter. The mean temperature for this season varies between 60° for the Gulf coast and 15° for the extreme northern part of Wisconsin. In the northern part of the valley the cold is sometimes so intense that the thermometer sinks to the freezing point of mercury.

The extreme of heat and cold would give a continental climate if this extreme were not accompanied by a profusion of rain. The southerly winds, laden with moisture, distribute this moisture with great regularity over the valley. The amount of rainfall, greater in summer than in winter, varies, from the Gulf of Mexico to Wisconsin, from 63 inches to 30 inches. On the Atlantic coast, where the distribution is more equal throughout the year on account of its proximity to the ocean, the amount varies, from Florida to Maine, from 63 to 40 inches. The atmospheric movements on which, to a great extent, the climatic conditions of the eastern United States depend, may be summed up as follows:

"1. That the northeast trades, deflected in their course to south and southeast winds in their passage through the Carribean Sea and the Gulf of Mexico, are the warm and moist winds which communicate to the Mississippi valley and the Atlantic slope their fertility.

"2. That the prevalence of these winds from May to October communicates to this region a sub-tropical climate.

"3. That in the region bordering on the Gulf of Mexico, the atmospheric disturbances are propagated from south to north; but in the northern and middle states, owing to a prevailing upper current, from west to east.

"4. That while this upper current is cool and dry, and we have the apparent anomaly of rain storms traveling from west to east, at the same time the moisture supplying them comes from the south.

“5. That, in the winter, the south and southeast winds rise into the upper current, while the west and northwest winds descend and blow as surface winds, accompanied by an extraordinary depression of temperature, creating, as it were, an almost arctic climate.

"6. That the propagation of the cold winds from west to east is due to the existence of a warmer and lighter air to the eastward.

"7. That in summer the westerly currents seldom blow with violence, because, in passing over the heated plains, they acquire nearly the same temperature as the southerly currents, but in winter the conditions are reversed."

The line of conflict of these aerial currents, produced by unequal atmospheric pressure, shift so rapidly that the greatest changes of temperature, moisture, and wind, are experienced within a few hours, these changes usually affecting areas of great extent. In the old world, on the other hand, the mountain systems, generally running from east to west, offer an impediment, especially to the polar currents, and the weather is therefore not so changeable.

Wisconsin, situated in the upper and central part of the Mississippi valley, is subject to the same general climatic conditions which give this whole area its peculiar climate.

The highest mean summer temperature is 72° Fahrenheit in the southwestern part of the

state, and the lowest 64° at Bayfield, Lake Superior. During the months of June, July and August, the thermometer often rises as high as 90°, seldom to 100°. In 1874 the mercury reached this high point twice at LaCrosse, and three times at Dubuque, Iowa. There are usually two or three of these "heated terms " during the summer, terminated by abrupt changes of temperature. The isotherm of 70° (an isotherm being a line connecting places having the same mean temperature) enters this state from the west. in the northern part of Grant county, touches Madison, takes a southerly direction through Walworth county, passes through southern Michigan, Cleveland, and Pittsburg, reaching the Atlantic ocean a little north of New York city. From this it is seen that southern Wisconsin, southern and central Michigan, northern Ohio, central Pennsylvania, and southern New York have nearly the same summer temperature. Northwestward this line runs through southern Minnesota and along the Missouri to the foot of the mountains. Eastern Oregon, at 47° 30′ north latitude, has the same average summer temperature; the line then returns and touches the Pacific coast at San Diego.

The remarkable manner in which so large a body of water as Lake Michigan modifies the temperature has been carefully determined, so far as it relates to Wisconsin, by the late Dr. Lapham, of Milwaukee. It is seen by the map that the average summer temperature of Racine is the same as that of St. Paul. The weather map for July, 1875, in the signal service report for 1876, shows that the mean temperature for July was the same in Rock county, in the southern part of the state, as that of Breckenridge, Minn., north of St. Paul. The moderating effect of the lake during hot weather is felt in the adjacent region during both day and night.

Countries in the higher latitudes having an extreme summer temperature are usually characterized by a small amount of rain-fall. The Mississippi valley, however, is directly exposed in spring and summer to the warm and moist winds from the south, and as these winds condense their moisture by coming in contact with colder upper currents from the north and west, it has a profusion of rain which deprives the climate largely of its continental features. As already stated, the average amount of rain-fall in Wisconsin is about 30 inches annually. Of this amount about one-eighth is precipitated in winter, three-eighths in summer, and the rest is equally distributed between spring and autumn-in other words, rain is abundant at the time of the year when it is most needed. In Wisconsin the rainfall is greatest in the southwestern part of the state; the least on and along the shore of Lake Michigan. This shows that the humidity of the air of a given area can be greater, and the rainfall less, than that of some other.

In comparison with western Europe, even where the mean temperature is higher than in the Mississippi valley, the most striking fact in the climatic conditions of the United States is the great range of plants of tropical or sub-tropical origin, such as Indian corn, tobacco, etc. The conditions on which the character of the vegetation depends are temperature and moisture, and the mechanical and chemical composition of the soil.

"The basis of this great capacity (the great range of plants) is the high curve of heat and moisture for the summer, and the fact that the measure of heat and of rain are almost or quite tropical for a period in duration from one to five months, in the range from Quebec to the coast of the Gulf." Indian corn attains its full perfection between the summer isotherms 72° and 77°, in Illinois, Iowa, Missouri, and Kansas; but it may be grown up to the line of 65°, which includes the whole of Wisconsin. The successful cultivation of this important staple is due to the intense heat of summer and a virgin soil rich in nitrogen.

While Milwaukee and central Wisconsin have a mean annual temperature of 45°, that of southern Ireland and central England is 50°; the line of 72°, the average temperature for July, runs from Walworth county to St. Paul, while during the same month Ireland and England have a mean temperature of only 60°. In Wisconsin the thermometer rises as high as 90° and above,