On the supposed Sponge Spicules in Flint. 467 LV. — On the real nature' of the Minute Bodies in Flints, supposed to be Sponge Spiculce. By William C. Williamson. 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 spiculse 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-spiculse. 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 spiculse of sponges, but the separated prisms of disinte-grated shell-structures, belonging to some genus of the group of Margaritacece, 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-spiculse. Another point of difference was, that instead of being round, as is usually if not invariably the case with sponge-spiculse, 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 pointed contour, which characterized the detached specimens. Even the latter portion presented a differ-ent appearance from what we see in sponge-spiculse ; 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
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