attains a development sufficient to form true glaciers. On the western coast the principal ports are Guaymas, Mazatlan, Topolobampo, Acapulco, La Paz and Salina Cruz; on the eastern seaboard, Tampico, Vera Cruz, Puerto Mexico, Campeche and Merida. Of the numerous rivers, the most important is the Rio Grande, 1550 miles long, which forms a natural boundary between Mexico and the United States from El Paso to the Gulf. However, the conformation of the country does not admit of river navigation to any extent. According to the census of 1910, the population was 15,063,207, of which 20 per cent were whites, 43 per cent of mixed blood and the remainder of Indian extraction. In Mexico there are three distinct climates and a wide range of temperature. The hot country, _tierra caliente_, extends from the seacoast inland to an altitude of about 3000 feet. Here the mean annual temperature is between 80 degrees and 88 degrees, and the highest between 100 degrees and 105 degrees Fahrenheit. In this region the winter climate is delightful, except when severe gales sweep down from the north. In summer the extreme heat is not so great as in New York, because of the moderating effect of cool breezes. The temperate region, _tierra templada_, extends from 3000 to 6500 feet above sea-level, and it is here that the ideal climate of Mexico is found, the mean annual temperature being between 73 and 77 degrees Fahrenheit, with a total variation of possibly not over 6 or 8 degrees during a season. In this dry, clear atmosphere the hygienic disadvantages of the seacoast, the sharp, cold winds of the upper altitudes, sudden changes in temperature, heavy frosts, extreme humidity and harmful insects are unknown, and in the dry season there is no malaria. Tropical and semi-tropical growths flourish side by side, and there are estates on which wheat and sugar cane are raised almost in touch of each other. The cold country, _tierra fria_, extends from the 6500-foot level to the snow line, but here the term cold is used in a comparative sense, as distinguished from the heat of the seacoast. The average temperature runs between 59 degrees and 62 degrees Fahrenheit, with slight variations. At times, however, a norther will drive the mercury down to 40 degrees or 35 degrees and sprinkle the streets of Mexico City with white. As a rule, in Mexico the rainy season begins in May or June and ends in October. The annual rainfall varies greatly according to locality, ranging all the way from fifteen to fifty inches. Earthquakes are of common occurrence, especially on the western coast.