FOSSIL INVERTEBRATED ANIMALS. 499 



polyparia, a division of the latter has been established into free 

 and adherent, — denominations which require no definition. 



As some organized fluviatile bodies exist which have been 

 compared to sponges, and which, for a long time, have even 

 been ranged in that genus, another division of polyparia has 

 been necessitated into fluviatile and marine. 



The great quantity of calcareous or stony polyparia, which 

 have been found in the living state in the seas of warm cli- 

 mates, and the considerable masses which have been met with 

 in the fossil state in the composition of calcareous rocks, have 

 caused these productions of polypi to be considered as forming 

 a very notable constituent part of our continents, and as 

 capable of modifying, in an exceedingly rapid and powerful 

 manner, the surface of our globe which exists under the waters 

 of the sea. Nothing is more common than considerations of 

 this kind in treatises of geology, and especially with the authors 

 who flourished towards the close of the last century. Until 

 very lately, these speculations were founded, in general, only 

 on the observations of travellers, of mariners, and particularly 

 on those of Captain Cook, and other navigators, who have 

 traversed the South Seas and explored Australasia. Since 

 that period they have been corroborated in an especial man- 

 ner, first by Forster, and afterwards by Peron during his 

 voyage to New Holland, in the expedition of Captain Baudin; 

 and they have been adopted, in the sequel, by all zoologists 

 and geologists. It was easy, in fact, to perceive, that, if we 

 could admit that the animals which produce these polyparia, 

 designated in a general manner under the names of madrepores 

 or corals by mariners, and even by some geologists, could ger- 

 minate with as much rapidity as those which form the escharae 

 do, as we have learned from Spallanzani, the stony polyparia 

 must really produce, at the end of half a century, or less, by 

 means of strata superposed almost indefinitely, calcareous masses 

 of enormous extent and depth. But, in the first place, this 

 preliminary position is more than doubtful ; — it is more than 



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