ORIGIN AND NATURE OF SPRINGS. 7 



and passes downwards through pervious strata, 

 often finds vent in the sea, and thus the curious 

 spectacle is afforded of a fresh water spring bub- 

 bling up through a mass of salt water. Humboldt 

 mentions such a spring as occurring at the mouth of 

 the Rio Sargartos, off Cape Caloche, four hundred 

 yards from land. The inhabitants of Syracuse ob- 

 tain excellent fresh water by rowing off in boats into 

 the salt sea, and dipping it up into vessels as it rises 

 to the surface from the orifice below. It is difficult 

 to conceive of anything more paradoxical than this. 

 . If the mean annual temperature of the air is 

 taken as a standard of comparison, it will be found 

 that a majoritv of springs are thermal, or warm 

 springs, the temperature being above the mean of 

 the air of the locality in which they exist. The 

 earth is a great reservoir of heat, and as a rule the 

 heat increases the deeper we descend, and there- 

 fore 'deep springs uniformly supply warm water ; 

 cold springs usually flow from superficial rock or 

 soil coverings among hills, and in the gorges of 

 mountains. The elevated points in which they 

 originate are constantly under the influence of cool- 

 ing winds, and the shade of rocks and trees pre- 

 vents the action of the solar' rays in elevating the tem- 

 perature. It is not true that the gradual increase 

 of heat in the earth's crust is 1 F. for every fifty 

 feet of descent, although this statement is persist- 



