only active crater in Mexico at the present time. The great Malinche, or Malintzin--possibly named after the fair interpreter of Cortes--is a mountain of striking form, with its brow often snow-covered, upon the borders of the plateau of Tlaxcala, whilst the singular Cofre de Perote, with its box or coffin-like summit (13,400 feet above sea-level), is a prominent landmark of the eastern slope of Mexico's road from Vera Cruz, overhanging the summit of the Sierra Madre at the limit of the lowlands. Other high peaks are the Nevedo de Toluca, often snow-crowned, 14,950 feet; and Tancitaro, 12,660 feet. The Mexican mountains are mainly of underlying granite formation. The Jurassic, Cretaceous, and Tertiary Ages rocks are much in evidence throughout the country, whilst the highest ranges, as we have seen, are of volcanic origin. The singular plains of Yucatan are largely of calcareous formation, probably a Tertiary limestone. One of the most plentiful rocks over vast areas of Mexico, and that which forms the striking variation of scenery, is the mountain limestone, the excessively hard stratified crystalline rock of the Lower Cretaceous period. This rock formation extends right across Mexico--although isolated in places--from sea to sea, and its existence possibly goes to show that the Pacific and the Gulf were one, in earlier geological times. The predominating shades of these extensive strata are blue and grey; occasionally there are black bands alternating, and they lie upheaved at such angles as remind the traveller of the still more pronounced strata of the high summits of the Peruvian Andes.[25] The mountain limestone is of very hard texture; white and crystalline, it wears away but slowly under the action of the elements, although on the steep mountain tracks over which we are journeying we shall observe it broken into cubes like sugar, beneath the incessant trampling of hoofs, or worn away to silver-sand and borne down by the streamlets into the river valleys. [Footnote 25: See my book, "The Andes and the Amazon."] The rock-formations of the tablelands are those to which Mexico owes her fame as a silver-producing country, and it is in the high region, from 5,000 to 9,500 feet above sea-level, that her historical mines are encountered; and the zone of territory embraced by these well-known centres, from Pachuca to Guanajuato and onwards to Chihuahua, may be described without exaggeration as the richest argentiferous region on the surface of the globe. It is to the metamorphic formation that the abundance of mineral ores is due, and the igneous rocks which have given rise thereto--the granites, basalts, diorites, porphyries, and others. This metalliferous zone is more than 1,500 miles long, extending from the State of Chihuahua and Sonora in the north to Oaxaca and Chiapas in the south.