Between these two craters lies a group of volcanos of which Mayon is the most important, rising 9,000 feet. The highest peak in the archipelago is Mt. Apo, a volcano in Mindanao, which is 10,312 feet.

The United States Geographical Survey has been engaged for many years in making a topographic survey and map of the United States. The unit of survey is 15', 30' or 1° in extent each way, covering an area of one-sixteenth, one-fourth or one square degree. The unit of publication is an atlas sheet sixteen and one-half by twenty inches, and each sheet is a topographic map of one of the above areas. The scale of the full degree sheet is 1:250,000, that of the thirty minute sheet 1:125,000, and that of the fifteen minute sheet 1 :62,500. The artificial features such as roads, railroads, towns and cities, etc., as well as all lettering are in black; water features are printed in blue, while the features of relief, hills, mountains, etc., are shown by brown contour lines. Some maps of areas that are economically important are called special maps, and these as well as the ordinary maps are shown on the index map issued by the department on application.

Topographic maps have been made covering the greater part of the New England States, and the States of New York, New Jersey, Pennsylvania, Delaware, Maryland, Virginia, West Virginia, Ohio, Missouri, Kan

sas, Arkansas, Colorado, Oklahoma, Texas, Utah, Montana and California. Maps of sections of North Carolina, South Carolina, Kentucky, Tennessee, Alabama, Florida, Louisiana, Mississippi, Indiana, Illinois, Iowa, Michigan, Minnesota, Wisconsin, North Dakota, Nebraska, South Dakota, Wyoming, New Mexico, Arizona, Idaho, Nevada, Oregon and Washington have also been issued.

Each of the rectangles outlined in red on the index map shows the location and area of a quadrangle of which a topographical survey has been made. The price of the maps is five cents each of standard size.

Hydrography.

The chief hydrographic system of the United States is the MississippiMissouri system. Although the river from its source to its delta is known by two different names, yet its geography knows no artificial appellations, for whether flowing through the gloomy gorges of the Rocky Mountains near its source, or meandering through the prairies, savannahs or cypress swamps of the Southern States, it is still the "Father of Waters," the greatest river on the globe except the mighty Amazon of South America. That part of the river known as the Missouri takes its rise in a lake near the source of the Snake River on the continental divide. The Missouri flows northward through a succession of romantic

ravines and gorges, and at Fort Benton, the head of navigation, makes a bend to the northeast before finally taking a southeasterly direction.

The Yellowstone River, draining the wonderland of Yellowstone Park, is an important affluent. Where the river makes its leap of 300 feet at the Great Falls it forms a superb picture. Below the confluence with the Yellowstone the Missouri assumes the proportions it retains throughout its entire course, save that its depth increases; its course east is deflected by the escarpment of the Couteau du Missouri south and southeast. It now meanders through a vast prairie region, developing complex sinuosities and constantly changing the form of its alluvial banks. The Big Cheyenne, White, Niobrara and Platte rivers are its main affluents. The Missouri joins the Mississippi north of St. Louis, where the rivers are each a mile in width.

The Mississippi has its source in Lake Itasca in Minnesota, where it here flows north, and after passing through Winnebigoshish Lake takes a winding course to the south, close to the watershed of the St. Louis River, which enters Lake Superior at Duluth. The upper waters of the Mississippi naturally terminate at the Falls of St. Anthony at Minneapolis, which are rather a cascade, having a fall of 65 feet and a width of 1,000 feet. Below St. Anthony's Falls the main affluents are the Minnesota, St. Peter,

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Cedar, Turkey, Iowa, Skunk and Desmoines rivers, on the right bank, and the St. Croix, Chippewa, Wisconsin, Rock and Illinois rivers on the left.

Lake Michigan is connected with the Illinois River by means of a canal dug about ten feet below the level of the lakes.

The Mississippi, after leaving St. Louis, cuts its way through the barrier of the Ozark Hills and at the confluence of the Ohio enters an alluvial plain studded with lagoons and morasses, where the huge river like a snake coils and uncoils itself in the alluvial valley.

Levees or embankments have been constructed with vast labor to protect the low-lying land from inundations. These skirt the river on both sides for over 1,000 miles. Frequently crevasses occur, and millions of acres disappear beneath the floods.

Below Cairo the affluents of the river are the Arkansas, the Red, the St. Francis and the Yazoo rivers. Beyond New Orleans the river enters the Gulf of Mexico by means of several mouths.

The St. Lawrence River, including the Great Lakes, is the most dramatic river system on the globe. All rivers were originally a series of lakes that overflowed from one to another at the lowest points of their containing basins. In time the connecting streams cut connecting channels deep enough to drain the lakes, and the re

sulting river flows in a smooth and well-defined course. At one time the At one time the overflow of the Great Lakes passed into the Mississippi, either by way of the St. Croix River at Ashland, Lake Superior, or by way of the Illinois River where Chicago is located. But about 75,000 years ago the western watershed of the lakes became sufficiently elevated to cause the overflow to pass down the Niagara River, producing that marvelous cataract and the River St. Lawrence.

The Niagara River is industriously at work cutting a chasm for its waters back to Lake Erie, and many thousands of years hence will drain that lake as well as Lakes Huron, Michigan and Superior.

The Colorado River, which drains the Rocky Mountain plateau lying between Utah and Colorado, is a magnificent example of the power of water to cut a channel deep into the rocky crust of the earth. The great chasm is of unrivaled grandeur. The river seems to flow in a trough more than a mile in depth, where it roars in whirlpools and rapids between the colossal walls of sandstone, marble and granite that rise in imposing majesty, reared indeed by the invincible power of the torrent.

The basin of the Columbia River adjoins that of the Colorado on the north in the watershed of its chief affluent, the Snake River, but its northern section lies in British Columbia. The Snake River has its

source in the Wind River Mountains of Wyoming, and flows into the Columbia, in a serpentine fashion, at a point where that river first begins to turn to the west also. The Columbia has already received the waters of the Spokane and Yakima rivers. It breaks through the Cascade mountains, and, receiving the Willamette, flows some miles in width into a tidal estuary, draining a basin of 214,000 square miles.

The great basin that lies between the basins of the Colorado and Columbia and the Sierra Nevada mountains on the west is mostly an arid region. In the northeast angle lies Great Salt Lake, a shallow expanse of water which in past ages was at least nine times larger than its present area. It has no outlet to the ocean but rises and falls according to the seasons, its oscillations varying from 1,730 square miles to 2,200 square miles. Pyramid Lake, Lake Tahoe and Humboldt Lake, Goose Lake, Sevier Lake and Lake Malheur are other land-locked bodies of water in this great basin.

The Sacramento and San Joaquin rivers, watering the north and south sections, respectively, of the California valley, find their outlets in the Bay of San Francisco.

The rivers of the Atlantic slope form a separate coastal basin of New England, the largest river being the Connecticut. The Hudson is rather a marine channel than a river, and was

formerly connected with Lake George and Lake Champlain. The Delaware, Susquehanna and Potomac are remarkable for having penetrated the Alleghenies and draining wide territories west of the mountains. All the streams that drain the Atlantic plain resemble each other, having pure water in their upland courses, and winding sluggishly through the swamps that fringe the seaboard. The rivers of Florida have a direction of flow peculiarly their own and occupy the beds of old sea channels.

The Atlantic coast basin is supplemented by the basin of Alabama and Mississippi, whose rivers flow directly into the Gulf of Mexico.

A hydrographic feature of Alaska is its glaciers. The most notable are the Muir Glacier, at the head of Glacier Bay, and Malaspina Glacier in Yakutat Bay, which has an area of 600 square miles. The ice cliffs of Valdez Glacier are 15 miles long.

In the Philippines the largest river is the Rio Grande de Cagayan, which drains 16,000 square miles and flows northerly into the Pacific Ocean. South of the Cagayan basin the central part of Luzon is drained by the Rio Grande de la Pampanga into Manila Bay. In Mindanao the rivers flow north and south. The Rio Grande de Mindanao flows through a fertile and populous valley, discharging into the Celebes Sea. Its length is 200 miles. The Rio Agusan rises near the southern coast and flows for

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125 miles into an arm of the Sulu Sea. The largest lakes are Laguna de Bay, 25 miles long and 21 miles wide, and Lake Bombon, 14 miles long by 11 miles wide.

Climate.

The mean annual temperature of the United States is 52° F., which is that of its mean latitude, the 37th parallel. This is the same temperature that prevails in Europe on a line drawn through that continent along the south of England, although that line is 1,000 miles nearer the North Pole.

The United States has a hotter climate in summer than that of Europe, owing to the fact that its large land surface occupies a more southerly position, but in winter it is proportionately colder by reason of the great area that approaches and lies within the Arctic Circle.

The climate of the Atlantic zone is characterized by the regularity with which the normal temperature decreases from north to south. This regularity is caused by the fact that the Allegheny Mountains have а trend parallel to the Gulf Stream, the Arctic current, and the prevailing aerial currents that move from northeast to southwest and from southwest to northeast. While the climate of the uplands of the Alleghenies naturally varies with the altitude, yet both slopes, being swept by the same winds, have a similar climate.

There is an exception to this regularity in that the greatest summer heats of the Atlantic seaboard are hotter than the south of Florida, which is a distinctly insular climate, while the seaboard is bathed in the hot southwestern winds that prevail. In winter also the cold is increased by northwest winds, severe enough frequently to freeze oranges growing in northern Florida. Thus the variations of the thermometer, which amount to only a few degrees either few degrees either in winter or summer or from day to night in Key West, increase as we go north, the range being 20° F. at Charleston, 36° F. at Philadelphia, and 40° F. at Boston.

In general the rainfall bears a direct ratio to the temperature, and is therefore heavier in the Southern than in the Northern States.

In the Mississippi Valley the junction of the Missouri and Mississippi rivers may be regarded as the meteorological centre both of the central basin and of the whole United States. The mean temperature is 53° F., which oscillates between 20 and 23 degrees, but the extremes of temperature for winter and summer reach 126 degrees. The mean temperature gradually decreases from New Orleans to Duluth, while the range of temperature undergoes a corresponding increase of amplitude between the same two points as shown in the following table, based on observations made during 12 years:

The rainfall as a rule decreases according to latitude as we go north. Thus it is 50 inches at New Orleans, 39 at St. Louis and 28 at Milwaukee. But from east to west the decreasing precipitation is more marked. The mean annual rainfall between the Alleghenies and Texas ranges from 40 inches to 15 inches.

The Great Lakes exercise a moderating influence on the surrounding climate. In summer the temperature is lowered, while in winter it is raised several degrees in the contiguous territory. No part of the Mississippi basin is free from snow. A few flakes have fallen at New Orleans and Galveston, but they melt as soon as they fall, whereas in the northern part of the basin snow may lie two or more feet deep for several months. The abrupt changes of temperature sometimes produce the phenomenon of an ice storm, in which rain falling on the branches of the trees becomes crystal sheath of ice that sparkles in the sunlight like countless jewels.

a

Tornados, or cyclone storms, are peculiar to Kansas, Missouri, Iowa, and Illinois, and take place usually in May, June, or July. A funnel-shaped cloud is seen hanging out of a blackened sky. Its progressive movement varies from 15 to 70 miles an hour,