APPENDIX NO. 1.

"If we consider,"—says Humboldt in his Views of Nature,—"that in the north and south direction the difference of latitude between Santa Fé and the city of Mexico is more than sixteen degrees, and that consequently the distance in a meridian direction, independently of curvatures on the road is more than 960 miles, we are led to ask whether in the whole world, there exists any similar formation of equal extent and height, between 5,000 and 7,500 feet, above the level of the sea. Four-wheeled wagons can travel from Mexico to Santa Fé. The plateau whose levelling is here described is formed solely by the broad undulating flattened crest of the chain of the Mexican Andes; it is not the swelling of a valley between two mountain chains, such as the Great Basin between the Rocky Mountains and the Sierra Nevada of California in the Northern Hemisphere; or the elevated plateau of the Lake of Titicaca, between the eastern and northern chains of Bolivia; or the plateau of Thibet between the Himilaya and Quenlun, in the Southern Hemisphere."—Page 209, Humb. Views of Nature.