THE SNOW-LINE. 



the heat which prevails daily on the woody shores of the 

 Orinoco exceeds by 7° "2 that of the month of August at Pa- 

 lermo, we find, on ascending the chain of the Andes, at Po- 

 payan, at an elevation of 5826 feet, the temperature of the 

 three summer months of Marseilles ; at Quito, at an eleva- 

 tion of 9541 feet, that of the close of May at Paris ; and on 

 the Paramos, at a height of 11,510 feet, where only stunted 

 Alpine shrubs grow, though flowers still bloom in abund- 

 ance, that of the beginning of April at Paris. The intelligent 

 observer, Peter Martyr- de Anghiera, one of the friends of 

 Christopher Columbus, seems to have been the first who rec- 

 ognized (in the expedition undertaken by Rodrigo Enrique 

 Colmenares, in October, 1510) that the limit of perpetual 

 snow continues to ascend as we approach the equator. We 

 read, in the fine work De Rebus Oceanicis* " the River Gaira 

 comes from a mountain in the Sierra Nevada de Santa Marta, 

 which, according to the testimony of the companions of Col- 

 menares, is higher than any other mountain hitherto discov- 

 ered. It must undoubtedly be so if it retain snoio perpet- 

 ually in a zone which is not more than 10° from the equi- 

 noctial line." The lower limit of perpetual snow, in a given 

 latitude, is the lowest line at which snow continues during 

 summer, or, in other words, it is the maximum of height to 

 which the snow-line recedes in the course of the year. But 

 this elevation must be distinguished from three other phe- 

 nomena, namely, the annual fluctuation of the snow-line, the 

 occurrence of sporadic falls of snow, and the existence of gla- 

 ciers, which appear to be peculiar to the temperate and cold 

 zones. This last phenomenon, since Saussure's immortal 

 work on the Alps, has received much light, in recent times, 

 from the labors of Venetz, Charpentier, and the intrepid and 

 persevering observer Agassiz. 



We know only the lower, and not the upper limit of per- 

 petual snow ; for the mountains of the earth do not attain to 

 those ethereal regions of the rarefied and dry strata of air, in 

 which we may suppose, with Bouguer, that the vesicles of 

 aqueous vapor are converted into crystals of ice, and thus ren- 

 dered perceptible to our organs of sight. The lower limit of 

 snow is not, however, a mere function of geographical latitude 

 cr of mean annual temperature ; nor is it at the equator, or 



* Anglerius, De Rebus Oceanicis, Dec. xi., lib. ii , p. 140 (ed. Col., 

 1574). In the Sierra de Santa Marta, the highest point of which ap- 

 pears to exceed 19,000 feet (see my Rilat. Hist., t. ii., p. 214), there is 

 B peak that is still called Fico de Gaira. 



