OG ky ee 
composed either of amorphous particles or fragments with a 
rounded outline, probably portions of the chambers of foramenif- 
era. Besides these, there were a few straight rod-like par- 
ticles, which may have been derived from sponge spicules but 
I could not detect any indications of the presence of cocco- 
liths. After washing away the finer particles, the residue 
consisted, almost exclusively, of the entire and fragmentary 
skeletons of foramenifera, sponges and entomostraca, with a 
scanty intermixture of the remains of other organisms. There 
were but very few free, minute, mineral particles in the deposit 
and these, so far as I could judge, were iron pyrites. On 
subjecting a portion of the material to the action of Nitric 
acid, and heating; there was at first a certain amount of ef- 
fervescence, but the result proved that only a small portion of 
the material was dissolved by the acid, and that the greater 
part, including fossil shells, which, like those of the forameni- 
fera, were calcareous in their original structure, had now be- 
come either wholly or in part. silicified. The material itself, 
previously of a creamy yellow tint became, after treatment 
with the acid, of a snowy whiteness. Being desirous of as- 
certaining the extent to which the different fossils were affected 
by the acid, I tried examples of different forms separately 
with the following results ; 
1% Sponge spicules. These were not perceptibly affected 
by the acid and retained the same optical appearances 
both before and after treatment. 
2™ Foramenifera. The shells, previously opaque, or 
merely translucent by transmitted light, and white by 
reflected light, became as transparent as glass and the 
walls appeared reduced to great thinness. 
3" Entomostraca. A somewhat similar change was effec- 
ted in the shells of these animals as in those of the 
foramenifera, but the residual siliceous shell was thicker 
and less transparent. 
4" Echinoderms. Small fragments of shell of these orga- 
