Scientific Intelligence. — Geology. 443 



ance of the sea in summer nights is due to the presence of 

 myriads of minute molluscous animals. Dr Buckland next 

 spoke of the microscopic animalcules which fill our stagnant 

 ditches and lakes of fresh water ; the 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. Re- 

 cent observations have found the sediments of the lake of 

 Neufchatel 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 fall- 

 ing into water or other fluids fitted for their resuscitation ; 

 they are propagated by eggs, and by subdivision of the bodies 

 of individuals ; from one individual sixteen millions have been 

 produced in twelve days. Many of these infusorial animal- 

 cules have been noticed by former observers, and are figured 

 in the plates of the Encyclopedic Methodicpie, but they have 

 not till lately been shewn to be largely connected with geo- 

 logy. The almost universal presence of infusoria in lakes and 

 ponds explains the occurrence of a stratum of polishing stone 

 (Polier schiefer), composed entirely of siliceous shields of in- 

 fusoria, fourteen feet thick, and occupying the bottom of an 

 ancient lake of great extent, at Bilin, in Bohemia. Other 

 genera of infusoria, which secrete to themselves shells or 

 shields of oxide of iron, have been discovered by Ehrenberg, 

 in the marsh ochre that is formed annually in the ditches, 

 and even in cow tracks, on the meadows near Bilin. 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 at- 

 tracted also unorganised silex from the waters that held in 



