94 MICROSCOPICAL OBJECTS FOUND 



also incrusted the rocks of the vicinity.* An 

 analogous agency has doubtless consolidated the 

 hard sandy portions of the Chalk rubble covering 

 the Chalk rocks on the south side of Flamborough 

 Head, on the Yorkshire coast. An instrument 

 that could do so much might do more, and may 

 possibly have produced the crystalline limestone 

 of St. Fe, as well as the white calcareous rocks 

 of the Pampas and the Banda Oriental. 



An exceedingly interesting subject for enquiry 

 now suggests itself. In the recent deposit of 

 the Levant, we have generally an admixture of 

 calcareous and siliceous organisms. In some 

 localities the latter are more sparingly distri- 

 buted than in others ; in a few instances they are 

 almost entirely absent. The same admixture 

 occurs in the recent sands from the West Indies ; 

 the soft calcareous mud from the bottoms of the 

 lagoons of the coral islands, contain a consider- 

 able number of similar siliceous forms ;f and 

 corresponding results have been obtained in 

 most of the marine sediments from various parts 

 of the globe, examined by M. Ehrenberg. 



* Darwin's Journal, p. 578. First Edition. 

 t Darwin's Journal. Second Edition, p. 46.5. 



