270 ANNUAL OF SCIENTIFIC DISCOVERY. 



and 5 inches above high-water mark, — the air was perfectly calm 

 and the surface of the waters of the sea and port of Arica were 

 like burnished silver. 



For ten days subsequent to the 13th of August, shocks of earth- 

 quake — sometimes as many as 50 to 60 between sunrise and sun- 

 set — were frequent. 



A tidal wave occurred in the harbor of Yokohama, August 15th, 

 the day after the earthquake in South America. 



For further details see "American Journal of Science" for 

 November, 1868. 



THE USE OF EARTHQUAKES. 



From an article in the *' New York Times," the following ab- 

 stract is taken : — 



It is a matter of observation that everywhere around the coast- 

 line of every continent, the sea is constantly at work warring 

 against the land, crumbling away its edges, grinding it to pow- 

 der, and carrying the detritus away and spreading it out over its 

 own bottom. This process is slow, but it goes on forever, and 

 the result is that in time (that is, in the secular time in which geol- 

 ogy works) the structure of continents is entirely worn away, 

 and new ones are formed out of the ruins of the. former ones. It 

 is quite certain that our present land was formerly the bed of the 

 sea, and that continental masses once reared their forms where 

 now rolls the ocean. ' 



It is the earthquake and the volcano which place themselves in 

 opposition to this destructive tendency ; so thac we may regard 

 the igneous agents as in constant antagonism to the aqueous 

 agents, — the latter laboring incessantly to obliterate the land, 

 while the former are equally active in restoring it. What are 

 these igneous agents, and what is their source? 



It is a fact perfectly assured that, in proportion as we descend 

 into the earth, the heat augments, and the deeper we go the hot- 

 ter the earth is found to be. This increase is estimated at about a 

 degree of the thermometer additional warmth for every 90 feet 

 of additional depth ; or about 58° per mile. 



Now, though geology does not say that there may not be a solid 

 central mass in the interior of the earth, — •' kept solid in spite of 

 the heat by the enormous pressure," — it does say that an immense 

 range of terrestrial phenomena compels us to conclude that be- 

 neath the crust of the earth there is a sea of liquid fire, on which 

 the continents and the land underneath the ocean are floating. 

 This central fire is not only incandescent mtitter, but it is matter 

 in a state of energetic elasticity, continually reacting upon the 

 structure of the earth, and making itself felt more or less palpably, 

 — sometimes producing violent undulatory motions, and at other 

 times breaking!: throug^h the crust, and vomiting forth lava and the 

 central fluid. The former of these commotions are styled earth- 

 quakes ; the latter, volcanoes. There is little doubt that they 

 have a common origin, and, as has already been observed, it ia 



