12 



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 ot Ostraea though at- 

 tacked by the acid yet retained the form of the shell 

 perfect in silica. 

 6 l * Fish-scales. These were slowly but completely dis 



solved. 



7 1 ' 1 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 ol their shells in this mine- 

 ral, others, like the prisms of Inoceramus, though exposed to 

 the same influences , had completely 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- 

 letal 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 



