151 
in the Formation of Limestone . 
red and green colour of the water of certain shallow ponds in 
summer is, in some cases, due to swarms of Infusoria invisible 
to the naked eye. Some of these are figured and described in 
Shaw s Miscellany. Recent observations have found the 
sediments of the Lake of Neufch&tel to be full of Infusoria • so 
also is the mud at the bottom of every ditch and shallow pool. 
From the surface of this mud, whilst dry in summer the 
desiccated Infusoria are raised by the wind into the air, where 
they become mixed with rain, and fog, and snow, in all of 
which the microscope of Ehrenberg has detected them: they 
float with the atoms of dust we see twinkling in a sunbeam 
and return to life on falling into w'ater or other fluids fitted for 
their resuscitation : they are propagated by eggs, and by sub¬ 
division of the bodies of individuals: froin'one individual 
sixteen millions have been produced in twelve days. Many of 
these infusorial animalcules have been noticed * by former 
observers, and are figured in the plates of the Encyclopedia 
Mcthodiqne, but they have not till lately been shown to be 
largely connected with Geology. The almost universal pre¬ 
sence of Infusoria in lakes and ponds explains the occurrence 
of a stratum of polishing stone (Polier schiefer), composed 
entirely of siliceous shields of Infusoria , fourteen feet thick 
and occupying the bottom of an ancient lake of oreat extent 
at Bilin, in Bohemia. Other genera of Infusoria , which secrete 
to themselves shells or shields of oxide of iron, have been dis¬ 
covered by Ehrenberg in the marsh ochre that is formed annually 
m the ditches, and even in cow-tracks, on the meadow* near 
Berlin. The iron secreted from the water by each animal to 
form its shield becomes a nucleus, attracting other iron from the 
same water that supplied it to the animal; so that the iron ore is 
partly of animal and partly of mineral origin. The siliceous 
Infusoria in chalk flints seem to have been attracted to the 
alcyonic and spongiform bodies which often constitute the 
nucleus of these flints, at the same time that these nuclei 
attracted also unorganised silex from the waters that held in 
solution both silex and carbonate of lime. We find both these 
earths in warm springs that issue from volcanic rocks • e. a 
water charged with carbonate of lime is now issuing from the 
trap rocks of Clermont, in Auvergne, and deposits of siliceous 
stone are daily accumulating around the orifice of the geyser 
in Iceland. Recent discoveries of marine Infusoria in the sea 
water, co-existing with microscopic molluscs, lead us to infer 
from analogy the high probability that similar animalcules 
were not less abundant in the ancient seas. We may therefore 
expect to discover fossil Infusoria by the application of the 
microscope to thin slices of all siliceous and calcareous sedi¬ 
mentary rocks, that contain any other kind of marine or fresh¬ 
water remains. In this extension of the application of the mi¬ 
croscope from the living to the fossil Infusoria and foraminifers 
