seconds; longitude 77 degrees 35 minutes 7 seconds east of Paris, height 4026 toises, according to MM. Hodgson and Herbert.); Chimborazo is 900 toises higher than Mont Blanc; and Mont Blanc 653 toises higher than the peak of Nethou.* (* This peak, called also peak of Anethou or Malahita, or eastern peak of Maladetta, is the highest summit of the Pyrenees. It rises 1787 toises and consequently exceeds Mont Perdu by 40 toises.) These differences do not furnish the relative average heights of the Himalayas, the Andes, the Alps and the Pyrenees, that is, the height of the back of the mountains, on which arise the peaks, needles, pyramids, or rounded domes. It is that part of the back where passes are made, which furnishes a precise measure of the minimum of the height of the great chains. In comparing the whole of my measures with those of Moorcroft, Webb, Hodgson, Saussure and Ramond, I estimate the average height of the top of the Himalayas, between the meridians of 75 and 77 degrees, at 2450 toises; the Andes* (at Peru, Quito and New Grenada), at 1850 toises (* In the passage of Quindiu, between the valley of the Magdalena and that of the Rio Cauca, I found the culminant point (la Garita del Parama) to be 1798 toises; it is however, regarded as one of the least elevated. The passages of the Andes of Guanacas, Guamani and Micuipampa, are respectively 2300, 1713, and 1817 toises above sea-level. Even in 33 degrees south latitude the road across the Andes between Mendoza and Valparaiso is 1987 toises high. I do not mention the Col de l'Assuay, where I passed, near la Ladera de Cadlud, on a ridge 2428 toises high, because it is a passage on a transverse ridge joining two parallel chains.); the summit of the Alps and Pyrenees at 1150 toises. The difference of the mean height of the Cordilleras (between 5 degrees north and 2 degrees south latitude) and the Swiss Alps, is consequently 200 toises less than the difference of their loftiest summits; and in comparing the passes of the Alps, we see that their average height is nearly the same, although peak Nethou is 600 toises lower than Mont Blanc and Mont Rosa. Between the Himalaya* (* The passes of the Himalaya that lead from Chinese Tartary into Hindostan (Nitee-Ghaut, Bamsaru, etc.) are from 2400 to 2700 toises high.) and the Andes, on the contrary, (considering those chains in the limits which I have just indicated), the difference between the mean height of the ridges and that of the loftiest summits presents nearly the same proportions. Taking an analogous view of the groups of mountains at the east of the Andes, we find the average height of the coast-chain of Venezuela to be 750 toises; of the Sierra Parime, 500 toises; of the Brazilian group, 400 toises; whence it follows that the mountains of the eastern region of South America between the tropics are, when compared to the medium elevation of the Andes, in the relation of one to three.