82 MICROSCOPICAL OBJECTS FOUND 



The ferrugineo-calcareous matter obtained from 

 the decomposing sponges of Flamborongh Head, 

 contain abundance of large and perfect Fora- 

 minifera, and in some specimens calcareous sponge 

 spicula are distinctly present. All that I have 

 examined contained a much larger proportion of 

 sand grains, than occurred in the surrounding 

 Chalk. Thin argillo-calcareous partings separate 

 the horizontal beds of Chalk at the same locality, 

 but they exhibit nothing more than a few 

 Foraminifera, amongst some sand, and much 

 amorphous argillaceous matter. They evidently 

 indicate the occasional overflow of muddy 

 water, from some source not far distant. The 

 partings do not usually extend over very 

 wide areas, but appear to have arisen from 

 local causes. Siliceous granules are more or 

 less abundant in every specimen of Chalk which 

 I have seen, and also in that taken by Dr. 

 Mantell, from the hollow flint. The lim-C of some 

 of the calcareous Rotaliee from the chalk in the 

 same flint has disappeared, and its place been 

 supplied by pure and transparent silex, which 

 is the condition of nearly all the Foraminifera 

 found in the solid flint — a curious illustration 

 of the preference manifested by the siliceous 



