I have already referred, p. 43, to a hypsometric levelling, and to barometric measurements made from the junction of the Kanzas River with the Missouri to the Pacific, or throughout the immense extent of 28 degrees of longitude. Dr. Wislizenus has now successfully continued the levelling began by me from the city of Mexico, in the Equinoctial Zone, to the North as far as Santa Fé del Nuevo Mexico, in lat. 35° 38′. It will be seen, perhaps, with surprise, that the elevated plain which forms the broad crest of the Mexican Andes is far from sinking down, as had long been supposed, to an inconsiderable height. I give here for the first time, according to the measurements which we at present possess, the elevations of several points, forming a line of levelling from the city of Mexico to Santa Fé, which latter town is less than four German (sixteen English) geographical miles from the Rio del Norte. French Feet. Eng. Feet. Observer. Mexico 7008 7490 Ht. Tula 6318 6733 Ht. San Juan del Rio 6090 6490 Ht. Queretaro 5970 6363 Ht. Celaya 5646 6017 Ht. Salamanca 5406 5761 Ht. Guanaxuato 6414 6836 Ht. Silao 5546 5910 Br. Villa de Leon 5755 6133 Br. Lagos 5983 6376 Br. Aguas Calientes 5875 6261 Br. San Luis Potosi 5714 6090 Br. Zacatecas 7544 8040 Br. Fresnillo 6797 7244 Br. Durango 6426 6848 (Oteiza) Parras 4678 4985 Ws. Saltillo 4917 5240 Ws. El Bolson de Mapimi {3600 to 3837 to} Ws. { 4200 4476 } Chihuahua 4352 4638 Ws. Cosiquiariachi 5886 6273 Ws. Passo del Norte, on the} Rio Grande del Norte } 3557 3812 Ws. Santa Fé del Nuevo Mexico 6612 7047 Ws.