Usually earthquakes merely cause the earth to vibrate and even rumble, but do no harm. Sometimes, however, they cause cities to crumble to dust, start conflagrations which cannot be checked, and overwhelm whole provinces with terror. In our own country the one volcano that has been active in recent years, Lassen Peak, is located in the southernmost extension of the Cascade Range about 140 miles from the deep Pacific Ocean and two hundred from San Fran cisco, where some of the greatest recent earthquakes have taken place.
The Continuity of the Lands.—The same internal forces which cause earthquakes and volcanoes have heaved up the mountainous edges of the earth's rough tetrahedron so fully that aside from Ant arctica the continents almost unite into one connected series. There would be no insuperable difficulty in building a railroad from the southern tip of South America to Bering Strait, under the strait by tunnel to Asia, then to Suez, and so to South Africa. A branch might run to the Atlantic coast either at Lisbon or by tunnel to Eng land and Ireland. Another branch might run southward in Asia along the Malay Peninsula and then, with several ocean ferries, could be continued through the East Indies to Australia.
How Plants, Animals and Man Spread from Eurasia to North America.—The continuity of the lands has had a great effect on the distribution of plants, animals, and man. Eurasia is not only by far the largest of the continents, but has been most subject to changes of altitude, climate, and size. Hence it has been the region where new forms of life have developed most rapidly during untold millions of years. The horse, ox, camel, sheep, deer and elephant; the ash, poplar, onion and wheat; and countless other animals and plants, as well as man himself, al] originated there. In recent geological times a bridge of land connected Eurasia and North America where Bering Strait now lies, so that all the continents except Australia and Ant arctica were united. Moreover, the climate for a while was com paratively warm even in the Far North, so that plants and animals spread from Eurasia to America. For that reason when we go to Europe or northern Asia the oaks, pines, maples, birches, and other trees have a familiar look. The wild animals, too, such as rabbits, squirrels, foxes, bear, and many others are also essentially the same.
Early man seems to halie followed the plants and animals to America. Hence, the American Indians are more closely related to the Mongols of eastern Asia than to any other race.
Land Connections of Africa and of South America.—The tropical climate of Africa and South America causes their living creatures to differ greatly from those of temperate regions. Africa, however, can easily be reached by land from Asia. Hence such African animals as the elephant, lion, and horse-like zebra are closely related to the animals of Asia. Not only have animals been able to pass over from Asia to Africa, but the Indo-European, Semitic, and Negroid races have all done likewise. South America, on the contrary, can be reached by plants and animals from Asia only by way of North Amer ica and the Isthmus of Panama. Hence its animals and plants differ greatly from those of Eurasia. The little llama, for instance, is the nearest American relative of the camel. Again America has no native animal corresponding to the horse and zebra. The modern horse was introduced into both North and South America by man only after Columbus opened the way across the sea. The native Indians of South America are also so different from the native races of Asia that few resemblances can be seen comparable with those that are so marked when one compares the people of North Africa such as the Berbers and Bedouins with those of Europe and Asia.
The Breaks between the Continents: How the Australian Break has Isolated Australia.—Although the continuity of the lands has been of great importance in allowing plants, animals, and man to spread freely, the breaks in this continuity are no less important. One of these breaks has isolated Australia. Because of the inter vening sea that continent remained unknown even longer than Amer ica. When finally explored it was found to contain strange forms of life like the kangaroo, cassowary, coeka coo, honey-suckers, and the eucalyptus tree. The people, too, were found to have little in common with other races, and to be the most backward in the world. They had no permanent dwellings, no knowledge of farming, no ability to count more than four, and went about entirely nude. Like gorillas, they have thick skulls, small brains, thick broad noses, heavy arms, receding chins, thick necks, and hairy bodies.