282 Baron Humboldt on Hot Springs. 



volcanoes. I here refer to the Aguas calientes de Las Trin- 

 cheras between Porto Cabello and New Valencia, in South 

 America, and to the Aguas de Comangillas, near Guanaxuato, 

 in Mexico. The first spring, issuing from granite, indicated 

 90-3° C. ; the second, which issues from basalt, shewed 96-4° C. 

 The depth of the source of water of these temperatures, from 

 what we know of the law of increase of temperature in the inte- 

 rior of the earth, must probably be about 6700 feet (more than 

 half a geographical mile). If the cause of the heat of thermal 

 springs, as well as of active volcanoes, be the universally diffused 

 heat of the earth, then would rocks produce an effect only 

 through their capacity for, and their power of, conducting heat. 

 The hottest of all the permanent springs, those, namely, from 

 95° to 97° C. (204° to 207-6° F.), it is remarkable, are the 

 purest, are those that contain the smallest quantity of mineral 

 matter in solution. Their temperature appears, on the whole, 

 to be less permanent than that of springs between 50° and 74° 

 C, the invariableness of which, both in regard to temperature 

 and mineral impregnation, has been maintained so wonderfully, 

 within the confines of Europe at least, during the last fifty or 

 sixty years, i. e., since accurate thermometrical observations 

 and chemical analyses were made. Boussingault found that 

 the thermal springs of Las Trincheras had risen in temperature, 

 in the course of twenty-three years (from 1800, when my 

 jom-ney was jjerformed, to 1823), from 93-3° to 97° C. This 

 very smoothly-flowing spring is, consequently, at this time 7° 

 C. higher in temperature than the intermitting Geyser and 

 Stroki', the temperature of which has been lately more carefully 

 ascertained by Krug of Nidda. One of the most remarkable 

 proofs of the origin of these hot springs being due to the per- 

 colation of cold meteoric water into the interior of the earth, 

 and its contact there with a volcanic focus, was presented in 

 the preceding century, in connexion with the volcano of Jo- 

 luUo in Mexico, which was unknown to geography till after 

 my South American journey. When this mountain suddenly 

 made its appearance in September 1759, rising to a height of 

 1580 feet above the surrounding level, the two small streams 

 Rios de Cuitimba y de San Pedro disappeared ; but some time 



