The peculiarities of Australia do not mean that the continent is unfit for the forms of life found in other continents, but merely that the other forms have never had a chance to get there. This is proved by the way Eurasian animals flourish when introduced to Australia. For instance, under the influence of energetic British settlers that continent has become one of the world's great sheep-raising regions. European rabbits thrive wonderfully, and have become such a pest in pastures and farms that rabbit-proof wire fences have been built for hundreds of miles to keep them out. •Their astounding increase is due to the fact that the break between Asia and Australia has kept out foxes, wolves, and other flesh-eating animals.
How the Mediterranean Break Influences Commerce and Cli mate.—The most important of the breaks between the continents begins at Gibraltar. After stretching eastward for nearly two thou sand miles as the Mediterranean Sea it splits into two arms. One leads northward through the Bosphorus to the Black Sea. The other leads southward through the Red Sea to the Indian Ocean, but is interrupted by the Isthmus of Suez, which once obliged Europeans to sail around Africa to reach India. The Isthmus was such a hin drance that the Suez Canal was finally completed in 1869. Through Suez to-day passes practically all the commerce of Europe with the Far East and Australia.
In addition to all this the Mediterranean break is of great impor tance in its influence upon climate. Without the water evaporated from the Mediterranean Sea Italy, Greece, and the coasts of Asia Minor and Syria would be as dry and scantily populated as Persia or Arizona.
Why Gibraltar is of Supreme Military Importance.—Because Gibraltar guards the western entrance to the two-branched Mediter ranean break in the continents, it is the most important military position in the world. In case of war the country that holds it can prevent the ships of America and all the countries of northern Europe from reaching southern France, Italy, Austria, Greece, the Balkan States, southern Russia, and Turkey. Since Britain also holds Aden, she was able during the Great War to examine the cargo of every ship entering the Red Sea or the Mediterranean, and thus to prevent ammunition or ..ther supplies from being shipped to her enemies.
How Constantinople Rivals Gibraltar.—In the same way Con stantinople guards the northern branch of the Mediterranean break. The country that holds it is in a position to impose enormous suffer ing on Rumania and Russia by throttling their trade. For gener ations Russia coveted Constantinople so that she might have at least one outlet to the sea through ports that are not blocked with ice foi months each year. In the Great War the fate of Constantinople was one of the deciding factors. The British and French made great sacrifices in a vain attempt to open the Dardanelles. They hoped to secure a waterway whereby Russia could ship grain to her allies, while she herself received the guns and ammunition which her own factories could not supply. If they had succeeded the war might have ended
much sooner and Russia might have been saved from the terrible massacres, famine, and plague which prevailed under the Bolsheviki.
Why the North Atlantic Break is Important Climatically and Not Otherwise.—Another place where a tetrahedral edge of the earth breaks down is between western Europe and Newfoundland, where the Atlantic Ocean projects north to the Arctic. This has no great effect on shipping, but its climatic effect is far greater than that of the Mediterranean. Because the Gulf Stream and Atlantic Drift find this outlet to the north, the waters west of England and Norway are warmed so that the winds from them give all the countries of north western Europe a climate adapted in the highest degree to the pro motion of civilization. Without this warm branch of the ocean England and Germany would have a climate about like that of south ern Alaska and the neighboring parts of British Columbia to the eastward. Not only would agriculture be less successful than now, but stimulating changes of weather from day to day because of storms would be less frequent.
West of Newfoundland and still more to the west of Greenland, the North Atlantic break ceases to be an advantage, for it permits a cold current to come from the north. The presence of cold currents on both coasts is one reason why Greenland is covered with a vast continental glacier, a genuine ice-sheet. The other break leading to the Arctic Ocean at Bering Strait is of little importance, because it is so narrow and lies so far north.
The "American Mediterranean" Break.—The last of the great breaks, sometimes known as the American Mediterranean, is occupied by the Caribbean Sea and the Gulf of Mexico. Like the European Mediterranean it not only exercises a strong influence upon commerce, but is highly important climatically, and is closed by an isthmus across which men have found it worth while to dig a canal at enor mous expense. Since the American Mediterranean is surrounded by islands and can be entered at many points, no one place exercises a military control like that of Gibraltar or Aden. Yet in order to guard the Panama Canal the United States bought the Danish West Indies, or Virgin Islands, in 1917, and maintains an important naval station at Guantanamo in Cuba. It also has strongly fortified Panama itself, so that the Canal is now one of the world's most im portant military positions. The relation of the United States to Panama is strikingly like that of England to Suez. Just as England has been obliged to assume a protectorate over Egypt in order to protect Suez, so we have had to protect the Republic of Panama for r 5 the sake of canal. As England has military centers at Gibraltar and Aden whose importance is due largely to Suez, so our stations at Guantanamo, the Virgin Islands, and Honolulu owe their chief im portance to Panama.