108 MICROSCOPICAL OBJECTS FOUND 



devouring multitudes of the calcareous Polytha- 

 lamia, Escharae, and other parasitic corals, with 

 which most marine Algse are loaded. 



Something analogous to this has taken place at 

 the time of the accumulation of the guanos of 

 Ichaboe and Peru. It is obvious that all the vast 

 multitudes of siliceous Infusoria which they con- 

 tain have been taken up by the birds whilst in 

 the stomachs of molluscs and other soft animals. 

 That the latter feed largely upon them is abund- 

 antly proved ; and when we remember with what 

 a formidable rasping apparatus the palates of 

 many of these creatures are armed, we shall cease 

 to wonder that they can grind either calcareous 

 or siliceous structures to powder. Amongst the 

 Russian Fusulina limestones already noticed, 

 I mentioned that portions of the series exhibited 

 bands from fifteen inches to four or five feet thick, 

 consisting entirely of Fusulinse ; but above and 

 below these the Polythalamia diminish in number 

 until at length only a few specimens are found, 

 along with other fossils, scattered through the 

 limestone. In the latter instance it is evident 

 that, in addition to what has been contributed by 

 the calcareous cases of the Fusulinse, there has 

 been, as in the example of the Missouri Chalk, a 



