160 



Prof, Ehrtnhtrg on Fossil Infusoria, 



assimilated to itself a greater or less part of the empty siliceous shells. 

 The true wood-opal, in which the woody substance is changed into opal, 

 renders the opinion.probable that a peculiar opaline mass has supplant- 

 ed the decayed and dissolved parts of the woody substance, retaining 

 however its form. We cannot easily imagine the expulsion of the sili- 

 ceous shield-mass by the opal-mass, and of the latter filling its space i 

 therefore it appears conceivable that the opal may be probably formed 

 from the infusoria shells, simply by water or any other dissolving me- 

 dium except fluoric acid, just as dough is formed of meal. Unkneaded 

 dough contains stripes of meal,-~semi-opal has often stripes of infuso- 

 ria : both are hydrates. 



In the semi-opal of Bilin and of the valley of Luschitz were visible, 

 inclosed like insects in amber, 1. Gaillonella distans ; 2. Gaillonella va- 

 rimis, particularly the larger individuals ; 3. Gailloriella ferruginea j 

 4. siliceous needles of sponges. The first is mostly dissolved, at times 

 preserved as principal mass, with the outline rather rounded off, al» 

 though the connecting medium has quite a glassy appearance. The se- 

 cond is mostly well preserved, but rather rounded off ; the third is 

 sometimes well preserved in the bufF-coloured specimens, but on ac- 

 count of its minuteness does not admit of a determining character. The 

 latter however is not unimportant with regard to the question of the ac- 

 tion of volcanic agency : it may perhaps have been deposited in the 

 moist parts of the previously formed Polirschiefer. Upon heating this 

 yellow semi-opal, it became red and acted as iron. The red was the 

 articulated fibres of the Gaillonella: they could not therefore possibly 

 have been heated in the air. The tranquil horizontal stratification of 

 the Polirschiefer (exhibiting perhaps the yearly or periodical deposi- 

 tion of the layers) speaks also for a neptunian action. Hot vapours of 

 the volcanic neighbourhood might have much contributed to the puri. 

 fying of the mass, without actual fire. The semi-opal of Bilin removes 

 all doubt as to these organic relations. 



Very similar formations, with inclosed forms of organic origin, were 

 also apparent in the semi-opal from Champigny, that out of the Dolerit 

 from Steinheim near Hanau, and that from the serpentine formation 

 of Kosemitz in Silesia. The microscopical bodies inclosed in this 

 stone, very apparently of a spherical form, and never occurring largeVf 

 which are also attached externally to the semi-opal or hornstone 

 from Kosemitz as a white meal, and filling out its internal cavities, 

 might partly belong to the still existing genus Pyxidicula, They are 

 quite different from the stalactitic columns which produce the round 

 eyes in agate. 



