28 Mr. H. J. Carter on the Microscopic 
in the following “ footnote” to my above-mentioned paper in 
the ‘ Annals,’ viz. :— 
“Can it be possible after all, that this concentric lamina- 
tion is mineral and not organic—that is, that the calcareous 
layers are but a reproduction in form of the original spicules, 
which, during fossilization, have become dissolvedand furnished 
this solution for the new structure, as often seen in the chalce- 
donization of the vitreous sponges, or as agatoid layers round 
a grain of extraneous matter? ‘lhe examination of another 
slice of my specimen of Sestrostomella from the Jura strongly 
inclines me to this view”’ (‘ Annals,’ ser. 5, vol. xi. p. 35). 
Thus influenced, I lost no time in endeavouring to confirm 
the inference by grinding down slices of several species of 
fossil Calcispongiz to a minimum of at least 1-500th of an 
inch, or semitransparency, viz. Verticillites anastomans and 
helvetica, Peronellu dumosa, Oculosponyia dilatata, Elasmo- 
stoma acutimargo, and two or three others, when I came to the 
following conclusions :— 
1. That during fossilization, the organic matter of the 
spicule disappearing, the mineral matter, thus deprived of its 
cement, is set free. 
2. That while this is taking place the forms of the spicules 
are more or less destroyed and the mineral matter more or less 
passes into solution. 
3. That the forms of the spicules thus more or less destroyed 
run into each other so as to assume shapes totally different 
from what they were originally, while the rest of the caleare- 
ous material in a state of solution becomes deposited in the 
form of fibre composed of one or more concentric layers en- 
closing the lines of spicules. 
4, That although the slice when reduced to extreme thin- 
ness may present no distinct tri- or quadriradiates, yet one 
or more perfect ones may have come into view during the 
latter part of the reduction, when, atter every two or three 
strokes of the grinding, the slice should be transferred to the 
field of the microscope, lest the spicule be rubbed off altogether. 
Hence the advantage of grinding down the slice one’s self, 
otherwise such important facts might pass unnoticed. 
5. That if the tri- or quadriradiate of a Calcisponge cet. 
par. is thus seen, this should be sutticient to prove the nature 
of the fossil, although the next stroke of the grinding may 
destroy it, which is often the case. 
Observations. 
It is, however, the running together of the lines of the 
