The prisoner was moving forward as briskly as any of them, and the big fellow appeared to be paying special attention to him, as he was walking by his side most of the time.
The distance to the level plain below did not seem to be great.
Although the peaks of the Sierra del Fierro range seem high when looked upon from the level of the Rio Grande, they do not appear to be so lofty when viewed from the plateau upon which the actual ascent begins.
The level table-lands or plateaux of Mexico lie from four to nine thousand feet above sea level, making many distinct climates as one goes up or down.

These plateaux are girt by mountain chains.

The high summits are those of Cofre del Perote, 13,400 feet; Origava, 17,870 feet; Istaccihuatl, or the White Woman, 16,000 feet, and the famous Popocatapetl, known as "Smoking Mountain," which lifts its fire-scarred head 17,800 feet above the level of the ocean.
It seemed to the boys that the distance between the summit where they stood and the plain below might, even at the slow pace at which the outlaws were moving, be made by nightfall.

The eastern slope was not so rough and broken as that on the west.

In fact, the outlaws were now traveling down a declivity so clear of cliffs and breaks that the boys did not dare follow them.