158 



Prof. Ehreyiherg on Fossil Infusoria, 



of these two formations. There is probably also in Planitz a more 

 earthy form of this stone, similar to the loose Polirschiefer, which is 

 chiefly formed of the unchanged Gaillonella distans. 



A specimen of the Polirschiefer from Cassel, which M. Carus of 

 Dresden had the kindness to send me, and in which he had also recog- 

 nized organic forms, was particularly interesting. 



I found in the Royal Mineralogical Cabinet some specimens with pe- 

 trifactions of fish, Leuciscus papyraceus, from the same locality, 

 I have also lately been able, through the kindness of M. Keferstein of 

 Halle, to examine specimens of the stone from the Habichtswald near 

 Cassel. This Polirschiefer of Cassel contains seven different species of 

 shield-infusoria, between which is a loose, and, for the most part, silice- 

 ous cement, which cannot be plainly reduced to organic fragments. It 

 is worthy of notice that most of the forms in the Polirschiefer from Bilin 

 and Planitz are either extinct or as yet undiscovered ; while at the same 

 time those forms which resemble existing species, belong to such as are 

 not very striking, and therefore less sure for the detection of their iden- 

 tity ; but in the Polirschiefer of Cassel two of the most remarkable ex- 

 isting forms occur, namely Gaillonella varians and Navicula viridis \ 

 Navicala striatula appears also to occur in this Polirschiefer. GaillO' 

 nella varians diU^ Navicula viridis R'^^e'a.v both in the tertiary forma- 

 tion of Cassel and in the Bergmehl of San Fiore, and these have a form 

 related to that of A"a?;2CM/« Follis. Besides 1. Gaillonella varians, 2. 

 Navicula viridis, 3. Navicula striatula ? 4. Navicula Crux (comp. 

 Navicula Folks adulta), I have also found in the stone from Cassel, 5. 

 Navicula fulvajuv. ? 6. Navicula gracilis ? and 7- Navicula Cari, n. 

 species, — three less clearly defined species : the last however is very 

 numerous and is unknown to me. Besides these ascertained relations of 

 the distribution of the Infusoria-schiefer as Polirschiefer, the rich par- 

 cel sent by M. von Humboldt from Bilin and the valley of Luschitz has 

 given rise to very important observations. It consists of a small col- 

 lection of minerals from Bilin, made by Dr. Stolz of Bilin, of a larger 

 one by Dr. Reuss, and also of a great number of specimens collected by 

 M. von Humboldt. A careful geognostical drawing by Dr. Reuss ex- 

 plains the position of the rock-masses of that district. 



The infusoria rock of Bilin forms the upper layer (fourteen feet deep) 

 of the Tripelberg, which (differing from the Kritschelberg, with which 

 it was formerly confounded) is elevated about 300 feet above the level 

 of the brook Biela, It lies on a bed of clay, which is superincumbent 

 to the chalkmarl. Beneath these gneiss is found, as the base of all the 

 minerals of that district. The upper masses of stone lie west of the 



