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WONDERS OF GEOLOGY. Vol. I. 



with those of nature. The baths, erected there nearly twenty cen- 

 turies ago, present only heaps of ruins, and even the bricks of which 

 they were built, though hardened by fire, are crumbled into dust ; 

 whilst the masses of travertine around, though formed by a variable 

 source from the most perishable materials, have hardened by time ; 

 and the most perfect remains of the greatest ruins in the eternal city, 

 such as the triumphal arches and the Colosseum, owe their duration to 

 this source. 



How marvellous are those laws by which the humblest types of 

 organic existence are preserved, though born amidst the sources of 

 their destruction, and by which a species of immortality is given to 

 generations floating, as it were, like evanescent bubbles on a stream 

 raised from the deepest caverns of the earth, and instantly losing what 

 may be called its spirit in the atmosphere !" — Sir Humphrey Davy's 

 Last Days of a Philosopher. 



C. Page 78. — Caverns. — One of the most common appearances 

 in limestone caverns, is the formation of what are called stalactites, 

 from a Greek word signifying distillation or dropping. To explain 

 these, a brief description of the mode of their production will be 

 necessary. Whenever water filters through a limestone rock, it dissolves 

 a portion of it ; and on reaching any opening, such as a cavern, oozes 

 from the sides or roof, and forms a drop, the moisture of which is soon 

 evaporated by the air, and a small circular plate of calcareous matter 

 remains ; another drop succeeds in the same place, and adds, from the 

 same cause, a fresh coat of incrustation. In time, these successive 

 additions produce a long, irregular, conical projection from the roof, 

 which is continually being increased by the fresh accession of water, 

 loaded with calcareous or chalky matter ; this is deposited on the out- 

 side of the stalactite already formed, and trickling down, adds to its 

 length by subsiding to the point, and evaporating as before; pre- 

 cisely in the same manner as, during frosty weather, icicles, which are 

 stalactites of ice, or frozen water, are formed on the edges of the eaves 

 of a roof. When the supply of water holding lime in solution is too 

 rapid to allow of its evaporation at the bottom of the stalactite, it 

 drops to the floor of the cave, and drying up gradually, forms, in like 

 manner, a stalactite rising upwards from the ground, instead of 

 hanging from the roof; this is called, for the sake of distinction, 

 stalagmite. 



It frequently happens, where these processes are uninterrupted, that 

 a stalactite hanging from the roof, and a stalagmite formed imme" 



