Prof. Ansted on the Zoological condition of Chalk Flints, 6)C. 243 



It is to Professor Ehrenberg that naturalists are indebted, first 

 for the discovery of the infusorial and other animalcules of the 

 chalk, and next for the determination of various organic remains in 

 the solid substance of flint. These observations induced Mr, Bower- 

 bank in 1840 to examine with care numerous specimens of chalk 

 flint, and in doing so he was struck by the frequent recm'rence 

 of small patches of brown reticulated tissue constantly presenting 

 nearly the same appearance. " The occurrence of this tissue/^ 

 he observes in a paper published in the Transactions of the Geol. 

 Soc. (2nd ser. vol. vi. p. 181), "combined with the circumstance 

 of finding spicula exhibiting nearly the same form and size, and 

 always occurring in about the same proportion along with nume- 

 rous foraminated shells and other extraneous bodies, strongly in- 

 duced me to believe that the brown reticulated tissue was a por- 

 tion of the remains of the organized body, the shape of which was 

 represented by the flint nodules ; and the indications thus ob- 

 served equally inclined me to believe, that if these flints were 

 fossil organized bodies, they would almost inevitably prove to be 

 sponges." On the careful examination of a considerable number 

 of flints obtained from various localities, he found in all a perfect 

 accordance in the structure and proportion of this tissue and of 

 the spicula. I proceed to give a short account of the result of 

 these experiments. 



When thin slices of flint are examined under a good microscope 

 as transparent objects with a power of 120 linear, they present 

 the appearance of a turbid solution of decomposed organic matter, 

 containing fragments of extraneous bodies and portions of a dense 

 opake matter of a brown colour and sometimes of considerable 

 size. Treating these latter as opake objects, they are readily 

 distinguished to be made up of numerous cylindrical contorted 

 canals with occasional orifices of larger diameter, the walls of the 

 canals presenting an appearance of having been formed of thin 

 network like that observable in sponge, while spicula and minute 

 foraminated shells are sparingly distributed over the whole. The 

 smaller of the canals correspond with those by which the animal 

 of a sponge introduces the sea- water into its substance, the larger 

 ones being those for the excretion of the water. 



But this is not all. Even when the reticulated tissue is not to 

 be traced, its presence is still often indicated either by the form 

 in which the silex is moulded upon the tissue once there, or by 

 the spicula and minute shells which are suspended equally in all 

 parts : not being precipitated to one particular portion, as if they 

 had been deposited in a fluid, but entangled in the organized 

 matter, which had retained its form and texture during the pro- 

 cess of silicification. An examination of the chalky band forming 

 the exterior of the flint also exhibits a peculiar appearance under 



