GEOLOGICAL EVIDENCES. 35 



Among the rocks, which compose the solid crust 

 of the earth, there are many whose entire structure 

 proves that they once were liquid, and that they 

 solidified after an extremely gradual cooling. Such 

 are the wide-spread masses of granite, syenite, and 

 felspar-porphyry, which form the lowest layers of 

 many mountains ; and the trachyte, dolerite, and 

 basalt, so frequently met with in every country in 

 the world, which, as has been established as a fact 

 by the researches of geologists, have come up in 

 the liquid state through other rocks, and have an 

 unmistakeable resemblance to the matter thrown up 

 from many volcanoes that are yet at work. Several 

 of these minerals have even been formed by ar- 

 tificial melting in our chemical laboratories. 



Besides we know, from the great number of 

 active volcanoes, that are scattered over every zone 

 of the earth from the farthest south to the highest 

 north, as well as from the numberless hot springs, 

 that a great part of this primaeval heat is even 

 now beneath us. It is true that some have endea- 

 voured to account for volcanic eruptions and hot 

 springs by causes at work in certain places only; for 

 instance by the action of the air, and especially of 

 water, on metals that easily burn, such as potas- 

 sium, sodium, silicium &c, which they have sup- 

 posed to be stored up in large masses in the bowels 

 of the earth. Some have pointed to the considerable 

 rise of temperature, which is so often engendered 



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