Note 421 — Chapter V

Organic constituents, such as comminuted shells, and silicious and calcareous exuviæ of infusorial animals and plants, are sometimes found mingled in considerable quantities with mineral sands. These are usually the remains of aquatic vegetables or animals, but not uniformly so, for the microscopic organisms, whose flinty cases enter so largely into the sandbeds of the Mark of Brandenburg, are still living and prolific in the dry earth. See Wittwer, Physikalische Geographie, p. 142.

The desert on both sides of the Nile is inhabited by a land snail, and thousands of its shells are swept along and finally buried in the drifts by every wind. Every handful of the sand contains fragments of them. Forchhammer, in Leonhard Und Bronn's Jahrbuch, 1841, p. 8, says of the sand hills of the Danish coast: "It is not rare to find, high in the knolls, marine shells, and especially those of the oyster. They are due to the oyster eater [Hæmalopus ostralegus], which carries his prey to the top of the dunes to devour it." See also Staring, De Bodem van, N. I. p. 321.