1 1 



composed cither of amorphous particles or fragments with a 

 rounded outhne, probably portions of the chambers of foramenif- 

 era. Ik'sides these, there were a few straight rod-like par- 

 ticles, which may have been derived from sponge spicules but 

 I could not detect an\' indications of the presence of cocco- 

 liths. After washing awa)' the finer particles , the residue 

 consisted, almost exclusivel)' , of the entire and fragmentary 

 skeletons of foramenifera, sponges and entomostraca, with a 

 scanty intermixture of the remains of other organisms. There 

 were but \cr)' 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 ; 



r! 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 gla.ss 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'J Echinoderms. Small fragments of shell of these orga- 



