68 On the Phosphoric Strata of the Chalk Formation. 
' Geolojiical Transactions,' and the plates of vol. ii. of Par- 
kinson's 'Organic Remains,' may be consulted with pleasure and 
advantage. 
Tlie analysis of one of these sponges (a branching alcyonite) 
gave— 
Insoluble silicious matter and soluble silica . . 7 '68 
Phosphoric acid (equal to 61 '30 of bone earth phos- 
phate) 29-87 
Carbonic acid . ... • • . • . 8 '77 
Lime 42-29 
Oxide of iron and alumina . . . . . 6' 87 
Water, organic matter, fluorine,* and loss . . 4*52 
100-00 
Besides the sponges of definite form, there are oftentimes 
associated with them, in the midst of the other fossils, immense 
quantities of large amorphous spongoid bodies, somewhat resem- 
bling masses of recent sponge, which, though shapeless, possess a 
general uniformity of structure, so as to be immediately recog- 
nised by a practised eye. Externally some of them are much 
eroded. I hey are extremely heavy for their size, and are of 
every dimension, varying in weight from a few ounces to 8 and 
10 lbs. each. 
There is a peculiarity in this class of fossils; for whilst the 
general mass of organic remains in the green-marl beds indi- 
vidually agree in their chemical composition, these spongoid 
bodies differ from them and from each other, at any rate so far 
as relates to the proportion of phosphate of lime, since it ranges 
in them from 5 to 50 per cent. The richest ones usually lie in 
the centre of the bed, and the poorer below. They vary, too, in 
their own component parts, being richer towards the surface. 
This fact was suspected ; and to prove it, one of the largest, of a 
medium quality, was divided into sections, which, on being ana- 
lysed, gave the following results: — 
Exterior I 3-2-27 phosphate of lime. 
( 61-71 carbonate of lime. 
, . ,. , I 13-87 phosphate. 
Intermediate { ^-t, -, a u ^ 
( 67-14 carbonate. 
Interior ^ 10*26 phosphate. 
( 69" 17 carbonate. 
Theoretically this experiment was important, as tending to 
throw light upon" the source of the phosphoric acid so abundantly 
* The quantity of fluorine in these different fossils has not in any ease 
been determined. In some instances it is very considerable ; and were 
there any reason to view it as of agricultural importance, it would not 
have been omitted. — [.J. T. Way.] 
