406 



being in some entirely empty, and in others either partly or com- 

 pletely filled by siliceous crystals. 



Plate VII. Fig. 2. is a view of one of the sides of the above spe- 

 cimen, which possesses a striated and variegated appearance, from 

 its showing the perpendicular section of the tubuli, the contained 

 starred body, and the fossil wood which is interposed between the 

 tubuli. A careful examination shows that the stellated bodies them- 

 selves are in this direction striated. Fig. 3. represents a specimen 

 in which the marks of wood are very decided. The tubules in this 

 specimen have every appearance of having been formed by tere- 

 dines : possessing, in general, the same size and form with those 

 which are produced by this animal; being also lined with a similar 

 coating. The substance filling the tubules is constantly silicious ; 

 and sometimes, and particularly in this specimen, it is perfect agate, 

 in some parts of a reddish, and in others of a bluish white : the 

 stellated body being frequently to be seen, either in the centre, or 

 at the side of the agate. Fig. 5, 6, and 7> represent these stellated 

 bodies, with their surrounding tubules magnified to about five times 

 their natural size. When magnified to this degree, their substance 

 is discovered to be intersected by several curved lines, which doubt- 

 lessly formed the canals through which the fluid of the living animal 

 passed ; but the spaces of which being now filled with silicious 

 matter, an appearance is yielded very much resembling the plates 

 forming the exterior part of some echini and asteriae. 



As the animal nature of these bodies can hardly be doubted, their 

 examination in this department of our inquiry seems to be hardly ad- 

 missible ; but as by far the greater number of the specimens in which 

 they are contained, are evidently of vegetable origin ; and as all the 

 specimens which I have seen may be considered as varieties of fossil 

 wood, differing from other fossil wood, only by the accident of the 

 introduction of this particular substance, these observations may be, 

 perhaps, introduced here, without any considerable impropriety. 



