THE BOWELS OF THE EARTH. 305 



that deposited the silver ores, still at work. In the mines of this 

 region the miners, naked as savages, reeking with perspiration, 

 drinking pailful after pailful of ice water (twenty tons of ice, or, 

 in another case, ninety-five pounds per man, were used each day), 

 could labor but ten minutes at the drift (in imminent danger of 

 being scalded by striking a stream of hot water) before being 

 overcome by the heat and reeling to a cooler place. Fainting, 

 delirium, even death have been the effect of the reaction on 

 coming to the surface. Verily the Cuban proverb, that a Yankee 

 would be found to go after a sack of coffee though it were at the 

 gates of hell, was not far from the literal truth. 



However the rate of increase of temperature may vary, all 

 indications thus agree that less than ten miles below us a red 

 heat is attained and within twenty a white heat. Think of it ! 

 Ten miles below us it is red hot. Ten miles above we have the 

 pitiless cold, far below zero, of interplanetary space. To what 

 a narrow zone of delicately balanced temperature is life con- 

 fined ! 



From the deeper zones of higher temperatures we have sam- 

 ples furnished us by the volcanoes, opened along great cracks in 

 the earth, whence red or white hot foaming lava rises. They con- 

 firm our idea of the downward increasing heat of the earth. 

 These outpourings of molten matter from volcanoes give us some 

 idea also of the composition of the earth. To the path of investi- 

 gation thus opened we shall return in a moment. They have 

 also given rise to the very prevalent notion that the earth's sur- 

 face is but a solid crust over a fluid interior of the consistence 

 of lava. Observers on the Hawaiian Islands have even thought 

 they could hear the dashing of the lava waves beneath. But it is 

 not hard to see that the phenomena of volcanoes are far more 

 complex than the mere welling up of a fluid interior. The lava is 

 often more heavy than the crust, and it often stands at different 

 heights in neighboring vents. Moreover, contemporaneous, not 

 far distant vents sometimes furnish quite different material. This 

 could hardly be possible if all volcanoes had a common source. 

 The really essential and important part of a volcanic eruption is 

 the escape of gases, which are or soon become largely steam. 

 This forms the clouds which overhang a volcano, and descends in 

 time of violent eruptions in torrential rains, such as buried Pom- 

 peii in mud. Hence, some have supposed that a volcanic eruption 

 was due to the explosive action of sea water reaching the heated 

 interior. But it is perhaps more probable that the gases which 

 escape are originally contained in the lava and burst forth from 

 the interior of the earth on their own account wherever a crack 

 gives them a chance. According to this notion, the working of 

 volcanoes is not unlike that of a bottle of ginger ale. All that is 



VOL. XLVII. 25 



