The geographical conditions of Mexico and its geology and accompanying topography are peculiar, and indeed in some respects unique. Mexico has been termed "the bridge of the world's commerce,"[24] and, in fact, its geographical position between the two great oceans of the world--the Atlantic and the Pacific, and between, or joining, two great continents, North and South America--would seem to warrant such a description, especially having regard to the coming development of that part of the world and the rise of the Pacific Ocean in commercial importance. It is indeed a favourite theory of some writers that the commercial and civilised centre of the world is destined to shift from the Atlantic to the Pacific Ocean. This theory, which must be characterised, however, as open to much conjecture, has been lightly discussed elsewhere in these pages. But be it as it may, the situation of the cornucopia-shaped land of Mexico is of great and growing importance. Among the geographical features of almost international importance is the remarkable isthmus of Tehuantepec--now traversed by a railway--which separates by only 120 miles the deep waters of the Atlantic and Pacific Ocean systems. It is an isthmus of Panama of greater width, and certainly may form a "bridge of commerce." [Footnote 24: Humboldt.] Mexico--apart from the Yucatan peninsula--consists of a great triangular-shaped area, forming the tapering end of the North American Continent. It is bounded on the north and north-east by the United States; on the east by the Atlantic waters of the Gulf of Mexico, Gulf of Campeche, and Caribbean Sea; on the west and south by the Pacific Ocean; and on the south-east by Guatemala and British Honduras. Mexico is, therefore, a close neighbour of a part of the British Empire! The greatest length of the country is 2,000 miles nearly, its greatest width 760 miles, and its area 767,000 square miles. Thus it is nearly nine times the size of Great Britain, or as large as Great Britain, France, Germany, and Austria-Hungary all joined together; and this enormous area is inhabited at present by only fourteen or fifteen million people. Although Mexico lies half within and half without the tropics, it is generally known as a tropical country; and, indeed, the main gateway to it, Vera Cruz, is a tropical seaport, which may well give rise to such a general impression upon the part of the European traveller. A different impression, however, is acquired upon entering the country from the United States to the north. No tropic forests and bright-plumaged birds are encountered there as at Vera Cruz; instead are vast stretches of desert lying within the temperate zone, alternating with cultivated plains and interspersed with large towns. The traveller, roused by the shriek of the locomotive, looks forth into the clear dawn of the chill Mexican morning from the window of his sleeping-berth upon the Pullman car, as the train speeds over the plateau.