ST6 Ehrenberg and Hausmann on the Varieties of 



friable, meagre, but soft to the touch, and adheres to the tongue. 

 It swims on water for some minutes, but it afterwards sinks, ab- 

 sorbing water with a noise, giving out many air-bubbles, and 

 then expands gradually by irregular splitting of the laminae, 

 without being altogether separated. When exposed to heat, it 

 rapidly assumes a white colour. Here and there it is traversed 

 by veins of a pure, chalk-white, fine-earthy sihca, filled with 

 smaller or larger cavities. 



According to the information communicated by Colonel von 

 Hammerstein to Professor Hausmann, this silica has been 

 found in astonishing quantity in six different places of the 

 above-mentioned district, on the edge and first acclivity of the 

 great plateau of the Litnehurger Haide, covered to the depth 

 of only one foot and a half by the soil. The pure white silica 

 forms the upper bed, and has a thickness of 10 feet to 18 feet. 

 The coloured portion is beneath, and has been already pene- 

 trated to a depth of 10 feet, without the lower boundary having 

 been reached. 



The peculiar state of aggregation of this silica led Professor 

 Hausmann to conjecture that it might be analogous to the 

 Kieselguhr found in the turf at Franzensbad in Bohemia, and 

 that, like that substance, it might be composed of the siliceous 

 shields of infusory animals. A preliminary microscopic exa- 

 mination seemed to confirm this notion. In order to attain cer- 

 tainty on this subject. Professor Hausmann sent specimens to 

 the distinguished investigator of the infusory world. Professor 

 Ehrenberg of Berlin, who, by his extraordinary discoveries re- 

 garding the occurrence of fossil infusoria, has opened an en- 

 tirely new field of the most interesting investigations. He 

 requested that naturalist to examine these specimens of earth 

 more minutely, with a special view to these objects, and he re- 

 ceived, through his kindness, the intelligence, that hath earths 

 are entirely composed of beautiful and perfectly preserved in- 

 fusory coverings ; that these are very various, but still belong 

 only to known species, and to such as af'e found in a living 

 state in fresh water at the present day. In the earth No. 1 

 they are free from foreign admixture ; but in No. 2 they are 

 mixed with organic slime, and with the pollen of pines. During 

 even his first examination, Professor Ehrenberg succeeded in de- 



