THE REVOLUTIONS OF THE CRUST OF THE EARTH. 309 



and of the elements. According to Ebelmann, if the stratified rocks 

 had contained 1 per cent, of protoxide of iron, this would have been suf- 

 ficient to absorb all the oxygen of the air.* Now as iron is furnished 

 from an inexhaustible and continuous source, the fall of meteors, the 

 annual number of which is, according to M. Culvier Gravier, forty mill- 

 ions for the entire surface of the globe, this metal may, at a very dis- 

 tant- period it is true, absorb all the oxygen gas of the earth. 



Nitrogen also is diminishing in quantity. The electrical explosions 

 during storms increase the affinity of oxygen for nitrogen, the result of 

 which is an oxygenated compound of this gas. The latter, on coutact 

 with the air and with water, is transformed into nitric acid, which forms, 

 with the alkalies and with ammonia, nitrates very widely distributed in 

 nature. Nitrogen again is taken out of the air by guano and other 

 analogous deposits. M. Rivero, estimating for the Chincha Islands the 

 number of Guana's at 264,000 only, found that these birds have been able, 

 in six thousand years, to form the deposit of guano of these islands 

 which is estimated at thirty-six millions of tons. As the Guanas feed 

 upon fishes, and as the latter contain only 2.3 per cent, of nitrogen, while 

 the guano of Peru contains 14 per cent., M. Boussingault has concluded 

 that 10 kilograms (22 pounds) of guano proceed from GOO kilograms 

 (1,320 pounds) of sea-fishes, and that the 208,000,000 quintals of guano 

 (26,000,000 tons) are equivalent in capacity of nitrogen to 2,268,000,000 

 quintals (223,000,000 tons) of fishes. The 53,000,000 quintals (5,000,000 

 tons) of nitrogen must have been taken out of the atmosphere, as we 

 know of no other primitive source of this element. M. DArchiac t has 

 observed that the nitrogen withdrawn from the atmosphere cannot un- 

 assisted return to its source, and we know of no natural agent for its 

 restoration. The slow and continued action of the Guanas, then, by in- 

 creasing the quantity of guano and diminishing to an equivalent amount 

 the mass of nitrogen, must after a time modify the elementary constitu- 

 tion of the air. 



Man alone restores to the atmosphere a part of the nitrogen it has 

 lost by employing the guano for the improvement of his land, as he also 

 restores to the animal and vegetable kingdom the carbonic acid long 

 buried in the earth under mineral forms. 



It is no longer worth while to contest the fact of the diminution of 

 the aqueous mass of the globe. It is generally admitted that since the 

 epoch of the first sedimentation, the sea has diminished to an amount 

 equal to the mass of sedimentary rocks, minus the mass of the same 

 rocks dehydrated. But the possibility of a continued diminution of the 

 waters in the course of time is rejected, and for what reason ? We 

 know not, since the diminution of aqueous masses in the past is allowed. 

 The nucleus of the globe constantly furnished mineral substances, which, 

 by their disaggregation, their dissolution, and the evaporation of the 



* D'Arckiac, Coura dt PaUont. Strut., t. ii, \>. 'S.). 

 t Coins (IPah'ont. Stmt., t. ii. p. 



