M. Von Buch on the Silicificalion of Organic Bodies. 59 



to fossil oyster-shells, and that it is not a property of those 

 which are at present forming in the ocean. 



If not in every one, still we find in some oyster-shells la- 

 mellae, which are thick enough to permit us to observe clearly 

 the right angular fibres upon their surface ; and I do not 

 doubt likewise, by means of a greater magnifying power, and 

 very clear hght, the inclined plates of rhomboidal calcareous 

 spar would be discovered. 



Hence, every plate of an oyster shell would correspond to 

 the flat terminal plane of a six sided prism ; and the fibres, 

 when observed, are the lateral planes of this prism, by means ^ 

 of which, perhaps, the sphere of the operation of each secreting 

 orijan of the cloak of the animal will be denoted. 



Now, that which the oyster has taught us, will likewise be 

 easily believed to happen in the case of other testaceous animals, 

 which secrete carbonate of lime, in order that they, by means of 

 it, may construct for themselves a covering or dwelling. There 

 are also many shells which give rise to considerations similar to 

 those which occur on examining the oyster shell, and which, 

 perhaps, admit of being more clearly explained. The fibrous 

 structure of the shell of the Inoceramus had drawn attention 

 towards it, long before the true form and shape of the shell was 

 ascertained. An equally fibrous structure appears in Pinna, 

 Pachymia Gigas, (Sowerby, plate 505), the shell of Nautilus 

 Atari, and many others. 



After these reflections upon the true structure of shells, it 

 will be allowed me again to take up, and to follow out, the proof, 

 that it is only the animal slime, between the lamellae of the 

 shell, that will be silicified. 



There are found strewed in the plains of Mecklenburg and 

 Pomerania a great quantity of oysters, which are in very diffe- 

 rent degrees of silicification. They probably belong to the Ter- 

 tiary f(U'mation. Plate II. Fig. 3 and 4 represent some of these 

 oysters. Their silicification seems to have been effected with 

 violence ; the central wart of the small calcedonic system ap- 

 pears in general very thick, and the waves which extend from 

 it are very high and very broad. We see clearly how much 

 greater the space is which this siliceous jelly requires, than the 

 space of the organic substance, which the siliceous jelly 



