456 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1740. 



opened, there appears an oyster on each side, so well consumed, that one might 

 say it was well engraved there. These shells are also petrified, or turned to 

 stone. I opened one, in the middle of which there was an oyster quite entire 

 and at the same time, as it were, engraved in the other shell." 



I did not wonder at the shells being turned to stone, but it seemed strange 

 that the animal oyster should be petrified; nor did the author's reason of 

 this phenomenon appear to be sufficient. 



" When we take sand out of the first shell, we see the oyster, which is in 

 like manner consumed by time ; whence we must conclude, that these oysters 

 have been alive there, and that the water running out, the sand has insensibly 

 supplied its place, and that the oyster, as it died, left the print of its shape in 

 the shell. Thus there are some of these oysters, like those stones in which 

 we see a fish." 



It will hardly be understood what is meant by the shape of the oyster, a 

 soft and corruptible animal, being impressed on its shells, before the shells 

 themselves, by nature hard, were turned into stone ; nor will you easily come 

 into the author's opinion, that it should be possible for an oyster to imprint its 

 shape on the shells, in like manner as the skeletons of fishes leave their impres- 

 sion in soft earth, which is afterwards turned to a stone, for the most part 

 flaky. Therefore I thought it not amiss to explain this account by schemes of 

 a lithostreum, which I got whole out of a very hard stone of the mountain 

 Zijanken-Berg, near Dantzic, in 1736. 



It is to be noted, J . That the figured stones of Dantzic, containing many ex- 

 traordinary vegetable and fossil substances, especially of the mountains Hagels- 

 Berg, and Zijanken Berg, are formed of potter's earth and clay, mixed with a 

 little sand, grey, and generally very hard ; so that being beaten with an iron 

 hammer, they fly asunder like the vitrum fossile imperati. 2. That they con- 

 tain abundance of shells of cochlidae or conchas, very often entire, petrified, 

 but very distinguishable by their natural colours; sometimes, when the matrix, 

 as it is called, is less compact or hard, partly calcined, and partly petrified. 



Now in the abovemeiitioned lithostreum, if I mistake not, the same phae- 

 nomena appear, which le Bruyn has endeavoured, however obscurely, to de- 

 scribe ; therefore I took care to have an exact draught of this lithostreum, the 

 valves being opened with great circumspection. 



In these, the form of the animal remained entire; but the whole substance 

 of it was changed to a smooth, hard clay. This perhaps is what le Bruyn 

 meant, when he said, " In the middle - - - we see the oyster entire, and at the 

 same time it looks as if it was engraven in the opposite shell." 



Now it is well known, that in the inner part of most oysters, especially in 



