406 
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 ^ , 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 
admissible ; 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 acci- 
dent of the introduction of this particular substance, these observa- 
tions may be, perhaps, introduced here, without any considerable 
impropriety. 
Influenced by almost similar reasons, I shall here introduce some 
