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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 
aibulacral 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 zoophtyes, 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. Two chert casts of Spatangi from Shaftes- 
bury afforded results analogous to those obtained from chalk Kchi- 
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 
of the previously noticed cases, and the texture bore a greater affi- 
