70 On the Phosphoric Strata of the Chalk Formation. 
and other organic remains in sandstone, limestone, &c., or as casts of 
shells, or occupying their cavities. Upon analysis this substance is 
found to contain a large pro|!ortion of animal carbon. The rocks of 
fire stone at South Bourne, on the Sussex coast, are mottled with brown 
m )lluskite and hard amorphous concretions, consisting of carbon and 
phosphate of lime, mixed with sand and other extraneous matter. 
Casts of shells, of the genera Venus, Area, &c., entirely composed of 
the same kind of materials, are also abundant in these rocks. The 
lowermost bed of gault, at its line of junction with the green-sand 
beneath, at Folkstone and in many other localities, is largely composed 
of similar matter, resembling in ajjpearance the fossils called coprolites, 
hereafter described. The outer chamber of the ammonites and other 
shells, so abundant in the gault, are often filled with this substance. 
But the most interesting deposit of molluskite is in the Kentish rag of 
Mr. Bensted's quarry, near Maidstone. Tiiis phenomenon had not 
escaped the notice of that intelligent and accurate observer, who liberally 
placed at my disposal numerous shells, particularly of Trigonice and 
TerebratultB, which were filled with molluskite ; and large slabs of the 
sandstone full of concretionary and amorphous masses of the same. 
The latter, Mr. Bensted suggested, were derived from the fossilized 
bodies of the dead mollusks, which had become disengaged from their 
shells, and aggregated together, and had floated in the sea, until 
enveloi)ed in the sand and mud, which is now consolidated into the 
arenaceous stone named Kentish r;ig. Mr. Bensted, in illustration of 
this opinion, referred me to the following curious fact, related in the 
' American Journal of Science:' — In the yearJ836 a fatal epidemic 
prevailed among the shell-fish of the Muskingum River, in the State of 
Ohio. It commenced in April and continued until June, destroying 
millions of the mollusca that inhabited the beds of the tiibutary streams 
and the river. As the animals died, the valves of the shells opened, and, 
decomposition commencing, the muscular adhesions gave way, and the 
fleshy portions rose to the surface of the water, leaving the shells in the 
bed of the river. As masses of the dead bodies floated down the cur- 
rent, the headlands of islands, piles of drifted wood, and the shores of 
the river in many places, were covered with them ; and the air in the 
vicinity was tainted with the putrid effluvia exhaling from these accu- 
mulations of decomposing animal matter. The cause of the epidemic 
was unknown. 'Now nearly the whole of the shells in these beds of 
Kentish rag,' Mr. Bensted remarks, 'have their shells open, as if 
they were dead before their envelopment in the deposit. And from the 
large quantity of water-worn fragments of wood perforated with pholades 
imbedded with them, it seems probable that this stratum had originally 
been a sand-bank covered with drifted wood and shells, and presenting 
a very analogous condition to the phenomenon above described.' 
" Tlie gelatinous bodies of the Trigonice, Astrea, RostellaricB, Tere- 
hratulce, &c., detached from their shells, may have been intermingled 
with the drifted wood in a sand-bank; while in some instances the 
animal matter would remain in the shells, be converted into molluskite, 
and retain the form of the original." 
This very interesting and instructive account of Dr. Mantell's cannot 
