sists largely of organic matter, and if spread over the land would in time decay and disappear 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 combination 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.[1] 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 Von Hensen in 'Zeitschrift für 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.
