756 



MICROSCOPIC GEOLOGY : — FORAMINIFERA. 



of Diatom aceae (siliceous), 8 species of Foraminifera (calcareous), 

 and a miscellaneous group of objects (Fig. 403), consisting of 

 calcareous and siliceous spicules of Sponges and Grorgonias, and of 

 fragments of the calcareous skeletons of Echinoderms and Mol- 

 lusks. — The deep-sea Soundings which have been recently obtained 

 from various parts of the Ocean-bed afford results more or less 

 similar; the variety of forms, however, usually showing a diminu- 

 tion as the depth increases (§ 383). From an extensive com** 

 parison of the forms of recent Foraminifera brought-up from 

 different depths, Messrs. Parker and Rupert Jones consider them- 

 selves able to predicate the range of depth within which any par- 



Fig. 404. 



Microscopic Organisms in Chalk from. Gravesend : — a, h, c, 

 d, Textularia globulosa ; e, e, e, Eotalia aspera ; /, Textularia 

 aeuleata ; g, Planularia hexas ; h, Navicula. 



ticular collection may have been taken ; and thus to determine, in 

 the case of deposits of fossil Foraminifera, within what range of 

 depth they were probably formed. 



5S9. A collection of forms strongly resembling that of the Levant 



