in the Lower Greensand of Bedfordshire. 383 
The conglomerate of the Lower Greensand of Bedfordshire con- 
sists of ferruginous sand more or less indurated (which does not 
effervesce with hydrochloric acid), rolled pebbles, and light-brown 
nodules of phosphatic matter, which have an earthy fracture and 
often contain fragments of shells*. The nodules are often co- 
vered with perforations, which Mr. A. Wanklyn discovered to be 
the work of small bivalves+. Concretions of peroxide of iron 
are also found in this deposit. 
The fossil shells found in this bed exist in two different con- 
ditions, some being casts composed of the same material as the 
nodules, whilst the shells of others are replaced by oxide of 
iron, and are filled with the same material of which the bed is 
composed ; the indurated part of the bed also contains numerous 
impressions of shells. It is difficult to see how two formations 
presenting such marked points of difference can have been de- 
posited under the same conditions. 
The remains of organized bodies contained in this bed, as I 
have before stated, exist in two different states of mineralization, 
viz. as ferruginous shells and as phosphatic casts. The bed being 
very porous (a well has been sunk 50 feet deep for water) and 
largely impregnated with ferric oxide, shells (which, as is well 
known, consist chiefly of animal matter and calcic carbonate) 
would by the action of water have their calcic carbonate replaced 
by ferric oxide. In cases where the action was more rapid, only 
internal casts of the shells would remain. 
Shells which lived in the sea whilst this bed was being formed, 
and also shells derived from older formations, if deposited in 
this bed, would undergo this change. 
The phosphatic casts of shells must have been formed, or, at 
least, the shells must have been filled with phosphatic matter, be- 
fore they were deposited here, and the calcic carbonate afterwards 
dissolved by the action of water. The tricalcic phosphate would 
be protected from the solvent action of water by the presence of 
calcic carbonate, as proved by the experiments of Mr. R. War- 
rington, junr., described in a paper read to the Chemical Society. 
The ferruginous shells and phosphatic casts are found inter- 
mixed. 
The conglomerate contains lumps of hardened clay; and the 
so-called coprolites contain a much larger percentage of alumina 
than those of the Cambridge Greensand. ‘The analysis of the 
coprolites is made from a commercial sample, which contains the 
shells, nodules, teeth, and bones, all ground up together. The 
* Jn the interior of the nodules there are sometimes found specimens 
of a small species of Lima and of Cardium. 
+ Mr. Wanklyn has obtained several of these shells, which appear to be- 
long to two or three different species. 
