"240 DISINTEGRATION CHAP. V. 



sists largely of organic matter, and if spread 

 over the land would in time decay and dis- 

 appear almost entirely. It appears, however, 

 from recent observations on the snow-fields 

 of the Arctic regions, that some little meteoric 

 dust of extra mundane origin is continually 

 falling. 



The dark colour of ordinary mould is 

 obviously due to the presence of decaying 

 organic matter, which, however, is present in 

 but small quantities. The loss of weight 

 which mould suffers when heated to redness 

 seems to be in large part due to water in com- 

 bination being dispelled. In one sample of 

 fertile mould the amount of organic matter 

 was ascertained to be only 1*76 per cent. ; in 

 some artificially prepared soil it was as much 

 as 5' 5 per cent., and in the famous black soil of 

 Russia from 5 to even 12 per cent.* In leaf- 

 mould formed exclusively by the decay of 

 leaves the amount is much greater, and in 

 peat the carbon alone sometimes amounts to 



* These statements are taken from Hensen in 'Zeitschrift 

 fur wissenschaft. Zoologie' Bd. xxviii., 1877, p. 360. Those 

 with respect to peat are taken from Mr. A. A. Julien in ' Proc. 

 American Assoc. Science,' 1879 p. 314. 



