. T T ^ 



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 ; 



ri Sponge spicules. These were not perceptibly affected 

 by the acid and retained the same optical appearances 

 both before and after treatment. 



2" d 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 r 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 l Echinoderms. Small fragments of shell of these orga- 



