222 Geological Society : — Mr. Lonsdale on the 



shells of the chalk are often entirelj- or partially filled and enveloped, 

 and he states, that the results were the same, both with reference to 

 the exterior and the interior of the flint. In those cases in which 

 the Echinite is only partially filled, he infers that the portion so occu- 

 pied was originally a sponge, because its surface is uneven ; for had 

 the flint been deposited in an empty shell or Echinite, it would pre- 

 sent an uniformly flat surface. Again, he states, that the projecting 

 of the flint through the two openings of the Echinite, with an ex- 

 tension to a greater or less distance, is owing to the sponge having 

 grown outwards through these orifices ; and the envelopment of an 

 organic body by a tubular mass of flint, he explains by reference to 

 the habit of recent sponges to invest testacea or other marine bodies. 

 In some cases, he has found minute but deep depressions on the 

 surface of flints filling Galerites, and immediately opposite to the 

 ambulacral pores ; and he ascribes the origin of the depressions to 

 streams of water drawn in through the orifices to supply the wants 

 of the living sponge. 



Mr. Bowerbank was afterwards induced to extend his examination 

 to the flints which invest the zoophytic bodies of the Wiltshire chalk. 

 By carefully cleaning the interior of some of these flints, he discover- 

 ed spicula projecting from all parts, however different the character 

 of the inclosed body ; and the spicula appeared to have no reference 

 to it, none of them being found on its surface. Under the micro- 

 scope, the investing flint presented in every respect the same appear- 

 ance as that exhibited on the lower surface of the tabular flints, ha- 

 ving fragments of minute corals and small shells attached to the in- 

 ner surface. A thin slice exhibited the usual organic contents of the 

 common flint. He, therefore, infers that the tubular flint which in- 

 closes the zoophytes, owed its origin also to a sponge which invested 

 the organic nucleus. 



A comparison of the characters presented by the spongeous re- 

 mains of the flint, with a collection of recent sponges, has induced 

 Mr. Bowerbank to conclude that the fossils cannot be referred to any 

 of the established divisions of existing sponges. 



On examining the cherts of the greensand of Fovant in Wilt- 

 shire in the same manner, he found that the only differences between 

 them and chalk flints, existed in the coarser texture of the spongeous 

 fibre, the greater size of the interstices of the network, and the larger 

 dimensions of the imbedded extraneous bodies. The cherty nodules 

 of the upper greensand of Shaftesbury afforded similar appearances. 

 A black, semi-transparent nodule, with an outer coat resembling ag- 

 glutinated sand, was found under the microscope to contain nume- 

 rous contorted canals of various sizes, and a considerable number of 

 beautiful green spicula. Tw o chert casts of Spatangi from Shaftes- 

 bury afforded results analogous to those obtained from chalk Echi- 

 nites. 



Slices from a great variety of the greensand cherts of Lyme Regis 

 presented characters which agreed with the cherts of Fovant. A 

 specimen of flint from the Portland stone of Tisbury, and another 

 from Portland, gave a greater quantity of cellular structure than any 



