FOSSIL ANIMALCULES. 555 



and probably several hundred square yards in extent ; and it 

 was wholly made up of the siliceous shields of Bacillarice. A 

 similar deposit has been recently discovered by Dr. Drummond 

 in Ireland. The author has seen water, brought from a lake in 

 the island of St. Vincent, crowded with the shields of races of 

 Naviculce at present inhabiting it ; and a thick layer of mud, 

 which is being deposited at the bottom of the lake, is almost 

 entirely composed of them. 



1134. Some species of these Animalcules especially prefer 

 waters impregnated with iron ; and have the power of separating 

 the metal from its solvent, and incorporating it into their own 

 structures. Hence originates a soft yellow ochreous substance, 

 called Marsh Ochre or Meadow Earth, which is found in large 

 quantities every spring in the marshy neighbourhood of Berlin, 

 covering the bottom of ditches, and the hollows left by the foot- 

 steps of animals. The iron may be separated from the siliceous 

 shields of these Animalcules, which retain their form after it has 

 been extracted ; and, after the death of the Animalcules, the 

 iron forms a nucleus, to which more is attracted from the solution 

 in which they have lived. Similar ferruginous and siliceous 

 remains of Infusoria, have been found in ochreous substances 

 brought from the Ural mountains and from New- York ; and 

 also in a yellow earthy substance formed on the surface of the 

 mineral water of the salt works at Colberg, which is used for 

 iron-colour in house-painting. These discoveries, therefore, 

 open an immense field for inquiry, into the constitution of the 

 larger beds of ferruginous matter, deposited at former periods, 

 going'back from those which are known as bog-iron-ore. 



1 135. Of the more recent among such deposits of these Infu- 

 sorial exuviae, as may be regarded as fossil, are those of the 

 Beryhmekl) which is found in small masses in various parts of 

 Europe, and consists of a kind of siliceous earth mixed with 

 animal matter. On account of its nutritious qualities, this has 

 been employed as an article of food, especially in Sweden, where 

 it is very abundant in some localities. When microscopically 

 examined, it is found to be entirely composed of the remains 

 of animalcules, the siliceous shields of which inclose the origi- 



