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 de- 

 scribed (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 con- 

 traction, 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 cal- 

 careous 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 appear- 

 ance to the nodules. But they do not, as far as I can observe, con- 

 tain any spicula. I do not offer any opinion upon them, further tban 

 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 palaeonto- 

 logist 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 ex- 

 ternal 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. 



