CLIMATE AND CARBONIC ACID. 247 



Granite and all similar crystalline aggregates of silicates disintegrate, 

 and the separate minerals are decomposed chemically by the action of 

 carbon dioxide and moisture. Of the various compounds which result, 

 those of carbon dioxide with lime and magnesia are of most direct 

 interest in this connection, and those with lime may be discussed as 

 representative. 



The common combinations of lime and carbon dioxide are two : the 

 carbonate of lime, more specifically called the normal or monocarbonate, 

 and the bicarbonate of lime. The carbonate consists of one ion, 

 or chemical unit, of lime, CaO, combined with one ion of carbon 

 dioxide, COj. The bicarbonate consists of one ion of lime combined 

 with two ions of carbon dioxide. The carbonate is but slightly soluble 

 in water, the bicarbonate is easily dissolved. The carbonate is pro- 

 duced in the decomposition of silicates, and great amounts of it which 

 have been derived from this source in past ages are now contained in 

 limestones and other calcareous sedimentary rocks. Whether it exists 

 for a brief time in the weathering of silicates or is, as limestone, 

 exposed to atmospheric waters, the carbonate very readily combines 

 with carbon dioxide, and the bicarbonate is formed in solution. All 

 surface and underground waters contain bicarbonate of lime in greater 

 or less quantity, and enormous volumes are annually conveyed to the 

 sea. It is estimated roughly that the weight of the carbonate of lime 

 thus dissolved and contributed to the sea annually is 2,700,000,000 

 tons. This is about one-half of the total saline matter dissolved in 

 surface waters annually, and a portion of the remainder consists of 

 carbonates of magnesia, potash and soda. 



It has been computed by Professor Chamberlin and his associates 

 that the present supply of carbon dioxide in the atmosphere would be 

 exhausted by the decomposition of silicates in 5,000 to 18,000 years 

 at the present rate of consumption if there were no source of replenish- 

 ment. It is evident that the amount of carbon dioxide in the atmos- 

 phere at any time is the balance between supply and draft, and that it 

 may be more or less as one or the other preponderates. The next step 

 in forming the hypothesis, therefore, is to consider conditions which 

 may produce fluctuations of consumption and contribution. 



The consumption of carbon dioxide in weathering of rocks is an 

 effect of erosion, the familiar process which tends to reduce heights of 

 land to a low slope, declining to sea level. This tendency is opposed 

 by those internal forces of the earth's mass which depress sea bottoms 

 and relatively uplift continents and mountain ranges. The persistent 

 attacks of the sun's energy are directed against .the earthworks raised 

 by terrestrial forces. It is the fabled fight of the powers of light and 

 air against the powers of the dark underworld; and the former never 

 pause, whereas the latter sleep for ages, and, awaking, exert themselves 



