as a Constituent of the Atmosphere. 393 



immense masses of rock-material of which the chalk and 

 nummulitic limestone maybe taken as examples. Certain other 

 forms of animal life, such as Brachiopoda &c, also add their 

 influence to that of these lower forms; but their effects, how- 

 ever, are comparatively insignificant. The immense influence 

 exerted by these minute creatures is evident when we re- 

 member the vast masses of limestone entirely of organic origin 

 occurring in geological formations of all ages. Millions of 

 tons of limestone formed in this way occur in the solid crust 

 of the earth; and every ton of limestone contains about nine 

 hundredweight of dioxide. ISTor is this action confined to the 

 past. It is as active now, in all probability, as when engaged 

 in building up those immense deposits of white chalk so 

 abundant in some parts of Europe. Eecent deep-sea sound- 

 ings have revealed the fact that Foraminiferal life still flou- 

 rishes in the depths of the ocean, while the coral-polypes are 

 still building reefs in the warmer seas. On the other hand, 

 we must not forget that Darwin has shown that these coral- 

 polypes can only exist in water of a certain temperature, which 

 is only'attained in the warmer seas, and at a certain depth below 

 the surface of this water. Their influence, therefore, is limited 

 and confined to a comparatively small area of the globe. 

 Another circumstance which seems to have been overlooked 

 by most writers upon the subject is, that this dioxide fixed in 

 the solid state in this way is contained in the water, and not 

 in the atmosphere. It is generally supposed that all of it has 

 been derived from the air; but a very large portion must have 

 been obtained from submarine volcanic eruptions, and never 

 formed part of the atmosphere at all. Taking all things into 

 consideration, this cause, although very powerful, seems rather 

 to be one whose influence is only felt after the lapse of many 

 years, and, for activity, cannot be equal to the first one. 



The third action going on in nature effecting the purification 

 of the air is a strictly inorganic one. Included under this head 

 are such processes as the conversion of felspar into kaolin, the 

 decomposition of such silicates as hornblende, pyroxene, &c. 

 The large deposits of kaolin and decomposed felspar which are 

 met with in the earth sufficiently prove the magnitude of this 

 action. Calculations were made many years ago by Ebelmen 

 (see the JReceuil des Trav. Scient. deM. Ebelmen, Paris, 1855), 

 and have recently been recalculated and very clearly stated in 

 an excellent paper by Dr. T. Sterry Hunt, F.R.S.* A glance 

 at the numbers given in these memoirs will show the vast and 

 important effect which these processes must have exerted. 



* " Chemical and Geological Relations of the Atmosphere," American 

 Journal of Science, May 1880. 



Phil Mag. S. 5. Vol. 14. No. 89. Nov. 1882. 2 D 



