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On the supposed Sponge Spicule in Flint. 467 
LV.—On the real nature of the Minute Bodies in Flints, supposed 
to be Sponge Spicule. By Witi1am C. WILiiamMson. 
To the Editors of the Annals of Natural History. 
GENTLEMEN, Manchester, May 14th, 1846. 
AN exceedingly interesting example of friable chalk, found at 
Charing in Kent, having been placed in my hands by Dr. Man- 
tell, I have been enabled by an examination of it under the mi- 
croscope to correct an error into which I had fallen along with 
other observers, as to the real nature of those minute fusiform 
bodies, so common in chalk and chalk flints, and which have long 
been regarded as spicule of sponges. 
On examining a section of flint, even when it does not contain 
the usual forms of Xanthidia and Foraminifera, there will gene- 
rally be observed a number of small dark-coloured fusiform bodies, 
which have been regarded by geologists as sponge-spicule. The 
same things are frequent in the soft chalk of Cambridge and Kent, . 
as well as at other localities. 
A slight inspection of the Charing chalk, where the organisms 
are distinct and unmixed with amorphous matter, convinced me 
that the half of the small atoms of which the pulverulent mass 
was composed, consisted of bodies identical with those found in 
flint. Observing them to be calcareous and not siliceous, as I 
had expected, I was induced to make a more minute examination 
of them, and soon became convinced that they were not the cal- 
careous spicule of sponges, but the separated prisms of disinte- 
grated shell-structures, belonging to some genus of the group of 
Margaritacee, as defined by Dr. Carpenter in his valuable Report 
on the Microscopic Structure of Shells, published in the ‘ Report 
of the British Association’ for 1844. 
The first thing that struck me in the Charing specimens was 
their transverse lineation, a characteristic feature of shell-prisms, 
but one which I have never seen in sponge-spicule. Another 
point of difference was, that instead of being round, as is usually 
if not invariably the case with sponge-spicule, they were angular, 
having from four to six sides, which is also characteristic of shell- 
structures. The correctness of the view I had taken was soon 
settled by the discovery of a few specimens in which from two to 
half a dozen prisms remained in their original contact, exhibiting 
at one end the hexagonal reticulation so common in shell tissues, 
and at the other the pomted contour, which characterized the 
detached specimens. ven the latter portion presented a differ- 
ent appearance from what we see in sponge-spicule ; instead of 
being thickest*in the centre and gradually tapering away to each 
extremity, these organisms are nearly of equal thickness through- 
out a considerable portion of their length, and then taper off 
