.1838.] 



Prof. Ehrenherg on Fossil Infusoria. 



159 



Tripelberg on a projected mass of basalt, which forms the Spitalberg, 

 and on the other side of which (west) Grobkalk, with many discernible 

 petrifactions of small chalk sea animals (many Crinoideee) lie on the 

 gneiss. The himer masses (Saugschiefer and Semi-opal) lie in the 

 Polirschiefer towards the exterior upper part, the earthy below, dis- 

 posed often without order in layers, the inferior ones being almost ho- 

 rizontal. 



The particular attention paid to the Saugschiefer and semi-opal, 

 whose numerous transitions were exposed to view, has now given the 

 scarcely unexpected result that these also are in the closest connection 

 with the infusoria.— The Saugschiefer is, upon microscopical observa- 

 tion, plainly only a Polirschiefer, whose infusoria shells are cemented 

 by and filled with a formless siliceous matter, just as there are fossil 

 shells both filled and empty : this produces its greater specific weight, 

 and all its other characters. In the gradual transitions to the semi- 

 opal we see how the cement has increased at'the expense of the infuso- 

 ria shells, while the small shells have decreased in quantity and in 

 sharpness of outline. 



The formation of the serai-opal in the Polirschiefer appears to be 

 this, that it lies imbedded in it in nodule?, in the most minute transiti- 

 ons from the Saugschiefer. A close microscopical analysis of the most 

 varying semi-opals from Bilin, and the neighbouring valley of Lus- 

 chitz, has shown that all these stone nodules, which sometimes equal 

 flint in hardness and give sparks, consist partly of infusorial forms held 

 together by a small quantity of transparent siliceous cement, and part- 

 ly contain inclosed within them single mfusoria, but of a larger size* 

 just iis amber contains insects. It is often very plainly to be seen, that 

 the disposition of the Polirschiefer has not otherwise been altered, 

 either by its change into Saugschiefer (cemented and permeated by 

 amorphous siliceous matter), or by its change into serai-opal, than that 

 by some means a part of the infusoria shells, particularly the more de- 

 licate ones, have been eaten away or dissolved, with which another 

 part, especially of the larger forms, has been covered in an unaltered 

 state. In this process the stratified structure remains as fully visible 

 in the Polirschiefer as it had before been, and forms the stripes of the 

 semi-opal. The white and less transparent stripes are mostly well- 

 preserved layers of infusoi'ia. It is not improbable that a dissolving 

 medium may have acted upon the siliceous shells as drops of water or 

 steam act on meal. The parts in contact with it were gradually pene- 

 trated, and partly dissolved and changed into opal ; or the penetrating 

 matter, producing the opal, and which occupies but a small space, has 



