60 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 4,
in a mossy or dendritic fashion; but, as I have already said, there are
reasons for doubting that this shading had an organic origin. In some
specimens canals may be seen, some of them open, and some of them
filled with phosphate. They are numerous, but show no definite
arrangement. The minute dark spicular-looking bodies already described (see fig. 9) are always present, and usually much broken.
They appear to be more abundant towards the external surface; and
in some cases the structure there seems to be of a more definite
character for a certain small thickness. But whether this arises
from that part being better-preserved because less affected by contraction, or whether the constitution of it was originally different —
or whether the difference is apparent only, arising from a different
amount of mineralization, it is not easy to decide.
On the whole a microscopical examination of these bodies rather recalls me, so far, to my original opinion that they were sponges; while at the same time it must be admitted that in their external appearance they much resemble Alcyonaria. Contrary, however, to all the views, as far as I know, published previously to the first reading of this paper, I am decidedly disposed to give it as my opinion that the ordinary phosphatic nodules were originally organic bodies*.
If these organisms had contained siliceous spicula, they might be expected to have been preserved entire ; but if they contained calcareous spicula these will probably have been transmuted into phosphate, and, being imbedded in a ground of the same, many of them will have disappeared by being blended with the general mass, and others will be only partially distinguishable. Such partial obliteration has occurred to the septa of a Nautilus of which I possess a section.
The phosphatic casts of Cephalopods and Gasteropods, when sliced and placed under the microscope, present a somewhat similar appearance to the nodules. But they do not, as far as I can observe, contain any spicula. I do not offer any opinion upon them, further than that I believe them to be derived from organic matter, and to be either fossil Alcyonia, sponges, or molluskite. A point strongly in favour of this view is that the phosphatic matter appears to be universally adherent to the interior of the shell; and although it sometimes protrudes beyond the mouth of the shell, or out of the cavity of an Echinus, we do not find it moulded upon the exterior of the shell. The same may be said of the Crustacea.
If such organisms as these have been copiously preserved in this deposit, we may expect to find the Tunicata, Holothurida, and such like bodies, also phosphatized. Indeed I believe that a palaeontologist would find a wide field of interest in examining these nodules. But in order to success he must search the pits himself, and select his specimens from the unwashed stuff, because the trituration of the washing-trough, or "mill," effectually effaces all delicate external markings.
- I desire to bear my testimony to the satisfactory results obtained by
Mr. Sollas, who has submitted a larger number of these fossils to microscopical examination than I have done, and has determined several species to be sponges.
