IN THE MUD OF THE LEVANT. 107 



agents in producing the finest kind of mud ; and 

 this, when derived from such materials, appears 

 to be the same with Chalk."* May not much of 

 the amorphous calcareous matter which occurs 

 in the Coralline Oolite of Yorkshire have been 

 treated in this way ? Lithophagi are abundant 

 in the deposit ; Modiola inclusa is still fixed in 

 the hard corals into which it had bored ; whilst 

 the rounded and enamelled teeth of the Malton 

 fish are such as would be well adapted to crushing 

 calcareous organisms. 



If a few soft fluviatile Infusoria are put into 

 clear water, with nothing to feed upon except 

 beings like themselves, it is surprising what an 

 amount of their exuvia is accumulated in a few 

 days. If we allow a similar process to go on 

 amongst larger animals only feeding upon small 

 calcareous creatures, instead of the soft tissues 

 of Infusoria, we may readily conceive that in 

 the space of hundreds of years an enormous 

 amount of amorphous calcareous matter would be 

 accumulated. Even those animals which are 

 phytophagous must contribute to this, for they 

 cannot feed upon a single marine plant without 



* Darwin's Journal. 1st Edition, p. 553. 



