nisms were nearly entirely dissolved by the acid leaving 
only a slight amorphous residue. 
5'? Mollusca. Detached prisms of the shells of Inoceramus 
which were very numerous in the deposit, were strongly 
attacked by the acid and completely dissolved, but 
very minute shells of a species of Ostraea though at- 
tacked by the acid yet retained the form of the shell 
perfect in silica. 
6" Fish-scales. These were slowly but completely dis 
solved. 
7‘: Coprolites. Small cylindrical pellets most . probably 
coprolites, were readily attacked by the acid and dis- 
solved with the exception of a residual reddish  floc- 
culent sediment. 
It will thus be seen that the degree, in which the various 
fossils were silicified and suffered alteration in their originally 
calcareous structure, varied considerably in amount; that whilst 
the foramenifera and entomostraca became so infiltrated with 
silica as to retain the perfect form of their shells in this mine- 
ral, others, like the prisms of Inoceramus, though exposed to 
the same influences, had compictely retained their normal 
condition. 
Structure of the Sponge Spicules. 
The Sponge spicules of this deposit, including under this 
term the individual siliceous bodies of exceedingly varied forms, 
which, either disconnected or attached together, form the ske- 
lctal support of the living organism, are exceedingly numerous, 
and with the exception of a few small fragments of the ske- 
leton net-work of the Lithistidae and Hexactinellidae are isolated 
from each other. Seen under a low power and by reflected 
light the spicules with few exceptions have a complete outline 
and an aspect like that of ground glass. When mounted in 
Canada Balsam and examined by means of a higher power 
