Another region in which the mountains have been reduced to inconspicuous heights is the Laurentian Plateau, the area around Hudson Bay. These mountains were very ancient and were worn down long, long ago. In some regions like southern New England, as the mountain structure has been worn down, it has left here and there a residual height like Mt. Monadnock which has not been fully reduced.
Although the general features of such a country are those of hills and valleys and it has little of the appearance of a plain as one passes over it, yet it will be found that the uplands have a general uniformity of elevation. Such an area is called a peneplain. The residual mountains which rise above the general level of the country and of which Monadnock is a sample have been named monadnocks. This is simply a name for a mountain left above a region which has been cut down by erosion to an irregular plain.
200.Mountain Peaks. -In mountain regions the features which are often most impressive are the serrated peaks which rise above the main mass of the mountains. The shapes of these peaks vary greatly indifferent mountain regions and tend to give individuality to the moun- tains. The peaks have been formed by erosion, and their peculiarities are due to the different kinds and positions of the rocks from which they have been carved.
The younger mountains which have not been subjected to erosion for a long time do not show the peak and ridge structure. Their personal characteristics have not had time enough yet to assert themselves. All these peaks are the result, not only of original uplift, but of subsequent carving.
THE TETON RANGE.
201.Mountain Ranges. -As a rule mountains are found in ranges. The mountains in the range are by no means all the same elevation, nor is the range necessarily continuous, there being often gaps along its course. Neither were all ranges in a mountain region elevated at the same time. Those which make up themountain region of the western United States differ much in the time of their el- evation.
202.Earthquakes. -In mountain
regions which are young or still growing, earthquakes are not uncommon. These are due to breaks or slips of a few inches or a few feet in the rock structure. From the place at which the break or slip takesplace the motion is transmitted through
FAULT LINE OF AN EARTHQUAKE.
the rock mass to the surface, where it causes sudden and often tremen- dous shocks. These slippings may occur occasionally for ages along the same fault line. Sometimes they are intense enough to cause great damage; at other times only a slight tremor is felt.
The rapidity of the transmission of the shock differs with the kind of material through which it is transmitted, varying from a few hundred feet to several thousand feet per second. The nearer a place is to the break or slip the greater is the intensity of the shock. Sometimes thecrack or fault along which the movement occurs reaches to the surface and makes the displacement apparent.
If an earthquake originates under the sea, a great wave may be developed which rushes inland from the coast, causing great destruction. One of the most fearful of these waves occurredat Lisbon, Portugal, in 1755, sweeping
FENCE BROKEN BY SLIPPING
OF THE EARTH ALONG A FAULT LINE.
away thousands of people who had
THE RESULT OF AN EARTHQUAKE.
PLACEE MINING IN THE SIERRAS.
The sand is washed from the gold by huge streams of water.
rushed into an open part of the city to get away from the falling buildings caused by the earthquake shock.
Sometimes earthquakes are followed by terrible fires which cannot be extinguished on account of the disarrangement of the water supply. This was the case in the San Francisco earthquake.
203.Products of Mountain Regions. -When rocks are foldedand crushed, in forming mountains, heat is generated, and heated water under pressure acts upon the com-ponents of the rocks and dissolves some of their minerals, which accumulate in cracks and crevices called veins. When the overly- ing beds have been worn away, these mineral veins, formed deep below the surface, are exposed and can be mined. Mountains are therefore the great mining regions.
In this country mining is a most important industry in the Sierra Nevada Mountainsand in the Appalachian region. In one are found great quantities of copper, silver andDEEP DOWN IN THE CALUMET AND HECLA MINE.
The world"s greatest copper mine.
gold, and in the other iron and coal. In the old Laurentian Mountain region, near the Great Lakes, much copper is found. The Alps and the Pyrenees are among those mountains that have few minerals.
If mountains are not too high, they are also regions of forests and furnish great quantities of lumber. The surface is so rough that agriculture is not easily carried on, but they have great areas of pasture which often support large herds of cattle, sheep, and goats.
204.Effect of Mountains on Climate. -All over the world wherepeople have the money and the leisure they are accustomed to go ei- ther to the mountains or the seashore in summer in order to get where it is cooler. They might for the same purpose travel northward in theTOP OF PIKE"S PEAK IN SUMMER.
Notice the snow and the rocks broken up by the freezing water.
northern hemisphere, but they would need to go many times as far to get the same fall of temperature.
In summer one must ascend a mountain on an average about 300 feet vertically to get a mean fall of 1℉., whereas one must travel over 60 miles north to get the same change. In winter one must ascendfarther on the mountain and travel not so far north, to get a change of a degree. As one ascends a mountain it grows colder and colder. In ascending a high mountain in the tropics one passes through all thechanges in climate which one would pass in going from the equator toward the poles.