Still onwards and upwards lies the way. One of the most remarkable railways in the world ascends this steep zone, and serpentines among sheer descents to gain the summits of abrupt escarpments, from which--a remarkable feature of the topography of the eastern slope of Mexico--the traveller looks down as into another country and climate, upon those tropical valleys which he has left below. This is the Mexican Vera Cruz railway. [Illustration: THE ATLANTIC SLOPE: TUNNEL AND BRIDGE OF THE INFIERNILLO CANYON, ON THE MEXICAN RAILWAY, IN THE STATE OF VERA CRUZ.] Let us pause a moment and gain a comprehensive idea of the character of Mexico's configuration and climate. It is to be recollected that Mexico, like other lands of Western America, is a country of relatively recent geological birth. The form of the country is remarkable. It shares the topographical features of others of the Andine countries of America--of tropical lowlands and temperate uplands, in which latter nearness to the heat of the Equator is offset by the coolness of the rarefied air of high elevations above sea-level. This structure is the dominant note of the scheme of Nature in Mexico--as it is in Peru and other similar countries--and the anthropo-geographical conditions are correspondingly marked. The region first passed is known as the _tierra caliente_, or hot lands. Its climatic limit extends up the slopes of the Sierras to an elevation of some 3,000 feet or more, embracing the lowlands, hot and humid generally, of the whole of the Gulf coast and of the peninsula of Yucatan, all of which regions are subject to true tropical conditions--the dense forests, the great profusion of animal life, the wonderful abundance and colour of Nature, and in places the swamps and their accompanying malarias, shunned by the traveller. But yellow fever and malaria are much less dreaded now than heretofore. In the city of Vera Cruz and in Tampico the new era of sanitation, brought about by British and American example and seconded by the Mexican authorities, has almost banished these natural scourges.