86 Prof. Ehreiiberg on Fossil Infusoria. 



and forms the upper layer of a Tripoli hill, which rises to a 

 height of about #00 feet above the surface of the Biela rivulet. 

 This eminence is different from the Kritschelberg, with which it 

 was formerly confounded. It reposes on a stratum of clay, 

 which rests on chalk marl. Under these occurs the gneiss, 

 which there forms the basis of all the rocks. The upper mine- 

 ral masses to the west of the Tripoli hill, repose on an erupted 

 portion of basalt which forms the Spitalberg, and on whose op- 

 posite side (to the west) Grobkalk, containing many well-known 

 fossil remains of marine animals (many Crinoidea) is seen lying 

 on the gneiss. 



The more compact masses (saugschiefer and semi-opal), oc- 

 cur more in the upper part, the earthy in the lower ; the two 

 are frequently mixed irregularly, and the lower layers are nearly 

 horizontal. 



The examination of the saugschiefer and semi-opal, with their 

 numerous transitions, has already afforded the unexpected result 

 that the latter as well as the former consists of infusory animals, 

 compactly united together. The microscope has proved that 

 the saugscliiefer is merely a polishing slate, whose infusory shells 

 are cemented together and filled by amorphous siliceous matter, 

 just as we have empty and full fossil shells of molluscous ani- 

 mals. This circumstance causes its greater specific gravity, and 

 all its other characters. We observe, in the gradual passage to 

 the semi-opal, that the cementing material increases at the ex- 

 pense of the infusory shells, while the latter diminish both in 

 number and distinctness. 



The semi-opal occurs in concretions in the polishing slate, 

 and the most imperceptible transitions may be remarked from 

 saugschiefer to the former. A careful microscopic analysis of 

 the different varieties of semi-opal from Bilin, and the neigh- 

 bouring valley of Luschitz, has shewn that all of them, even 

 those having the hardness of flint, and giving sparks like steel, 

 are sometimes entirely composed of a slightly transparent sili- 

 ceous cement of aggregated infusoria, and sometimes also contain 

 larger infusory forms, included like insects in amber. We can 

 often distinctly perceive that the layers of polishing slate have 

 undergone no other alteration during their conversion into saugs- 

 chiefer (a cementing and penetration by amorphous siliceous 



