SUPPLEMENTARY NOTES. 611 
In each of these cases, the greater number of the species are the 
same that now live in stagnant fresh-water ; some inhabit sahne 
mineral waters, and a few Uve in the sea. The total number of 
fossil species observed is twenty-eight, fourteen of which agree 
with living fresh-water species of Infusoria, and five with living 
marine species. The other nine probably belong to living species 
not yet discovered. In each of these four localities one species 
preponderates largely over the rest, and in no two cases is it the 
same species. The Polierschiefer of Bilin occupies a surface of 
great extent, probably the site of an ancient lake, and forms 
slaty strata of fourteen feet in thickness, consisting almost en- 
tirely of an aggregation of the siliceous shields of Gaillonella 
Distans. The size of one of these is about ^ of a line which is 
about -J of the thickness of a human hair, and nearly of the 
size of a globule of the human blood ; about twenty-three mil- 
lions of animals are contained in a cubic line of the Polierschiefer, 
and 41,000 millions in a cubic inch ; a cubic inch of Polierschiefer 
weighs 220 grains, of the 41,000 millions of animals, 187 millions 
go to a grain, or the siliceous shield of each animalcule weighs 
about the ^^ millionth part of a grain. Siliceous remains of 
Infusoria have recently been found also in the Polierschiefer of 
Planitz and Cassel. 
M. de Humboldt has recently communicated to the Academy 
of sciences at Paris (February 20, 1837) a letter from Professor 
Retzius of Stockholm, in which he informs Ehrenberg that a 
substance called Bergmehl, {Farine de montagne,) analyzed and 
described by Berzelius, 1833, and found by him to contain Silex, 
animal matter, and crenic acid, is eaten in Lapland in seasons of 
scarcity, mixed with ground corn and bark, in the form of bread; 
in 1833 this occurred in the Commune of Degerfors. M. Retzius 
has discovered in this Bergmehl, nineteen species of Infusoria 
with siliceous shields. This deposit appears to be analogous to 
the Kieselguhr of Franzenbad. 
L'Institut, 22 Feb. 1837. No. 198. 
Ehrenberg has further ascertained that a soft yellow ochreous 
substance called Raseneisen, (Marsh Ochre, or Meadow Earth,) 
which is found in large quantities every spring in Marshes about 
Berlin, covering the bottom of ditches, and in the footsteps of ani- 
