IN THE MUD OF THE LEVANT. 91 



also that similar causes led to the formation of the 

 Cretaceous strata of both Europe and America. 



That in the strata below the Chalk the 

 evidences become more obscure, owing, pro- 

 bably, to some extensive metamorphic action that 

 has modified their structure, but that glimpses 

 may occasionally be obtained, indicating the 

 existence of similar phenomena, even as low 

 as the Silurian limestones. 



That though in some strata, as in the Chalk, 

 Foraminifera have been the principal instru- 

 ments in effecting these results, in others, 

 sponges, corals, molluscs, Echinoderms, and 

 crustaceans have contributed their quota to the 

 entire mass, and often in much larger propor- 

 tions than the Foraminifera themselves. This 

 distinction appears to mark the difference between 

 the deposits formed along exposed coasts and those 

 accumulating in the deeper or more sheltered seas ; 

 in some instances, as in the Coralline Oolites of 

 Yorkshire, Oxfordshire, Berkshire, and Wilts, 

 we find the remains of vast coral reefs regularly 

 imbedded in the stratified mass, and most probably 

 still occupying the position they did when tenanted 

 by living polypes. 



