AGE OF CORAL REEFS. 197 



With regard to the geological position of the 

 Actinias we can say nothing, because, if their soft, 

 gelatinous bodies have left any impressions in 

 the rocks, none such have ever been found ; but 

 their absence is no proof that they did not exist, 

 since it is exceedingly improbable that animals 

 destitute of any hard parts could be preserved. 



The position of the Corals on a Reef accords 

 with these series of structural gradation and ge- 

 ological succession. It is true that we do not 



SUCCESSION ON THE EEEF. 

 JEIalcyonoids. .. 



.Madrepores. 

 CORAL REEF .\Porites. 



Maeandrines. 



"Astrseans. 



find the Actinia in the Reef any more than in the 

 crust of the earth, for the absence of hard parts in 

 their bodies makes them quite unfit to serve as 

 Reef-Builders. Neither do we find Fungidae, for 

 they, like all low forms, are single, and not con- 

 fined to one level, having a wider range in depth 



