384: Mr. J. F. Walker on a Phosphatie Deposit 
amount of alumina with the fluorine and magnesia, in one ana- 
lysis, is 6°64 per cent.; of course, if a special analysis of the 
nodules and phosphatic casts (the adhering sand having been 
carefully removed) were made, the percentage of alumina would 
doubtless be greater. This would indicate that the phosphatic 
nodules had been formed of clay soaked in decomposing animal 
and vegetable matter, since the alumina could not be derived 
from either animal or vegetable sources. 
The question now to be considered is, whether all the remains 
of organic life found in this deposit are coeval with the deposi- 
tion of the bed. 
Mr. Seeley states that he has never obtained from this bed a 
fossil that is extraneous, and that they all appear to him to be 
“ denizens of the old sea-bed where they abound.” 
There are obtained from this deposit large masses of silicified 
wood resembling those found in the Purbeck, also small pieces 
of wood mineralized with phosphoric acid, and often bored by a 
new species of Pholas, which I have named Pholas Dallasit. 
It seems improbable that wood existing in two such different 
conditions should have been derived from the same source*. 
Amongst the remains of animal origin we find rolled bones 
and teeth of reptiles and fishes, also shells of Mollusca, existing 
(as before mentioned) in two distinct conditions. 
The phosphatic casts of shells are generally so much worn 
that it is impossible to identify their species with precision. In 
their general aspect they resemble those of the Kimmeridge and 
Oxford Clays. They consist of casts of Rhynchonella, of Car- 
dium, Arca, Pholadomya, &c., of Pleurotomaria, Chemnitzia, 
Natica, &e.; three or four species of Ammonites occur, of 
which Ammonites biplex is found in great abundance; several of 
the Ammonites retain their nacreous lustre. Phragmacones of 
large Belemnites have also been found. 
Part of the ferruginous shells also appear to have been derived 
from extraneous sources: amongst these I have obtained a spe- 
cimen of Hxogyra virgula and numerous specimens of Gryphea 
dilatata. These shells, on account of their shape, could not 
contain phosphatic mud when they were deposited. They are 
in a bad state of preservation, which may be due to two causes, 
—first, to their having been rolled; and secondly, to their having 
at the time of their deposition. lost part of their animal matter; 
therefore the removal of their calcic carbonate would be more 
rapid, and its replacement by the ferric oxide less perfect. 
The other ferruginous shells appear to be of the age of the 
* Since this paper was read, I have obtained a fine specimen of a cone 
probably belonging to a Cycadaceous plant of the Wealden age. Its 
length is 2°6 inches, and its circumference is 2°75 inches. (Pl. XIII. fig. 5.) 
