54 VESTIGES OF THE 



vvliicli are now established as annelides, or sea-worms, 

 a tribe of creatures still existing (nereidina and serpulina), 

 and which may often be found beneath stones on a sea- 

 beach. One of these, figured by Mr. Murchison, is 

 furnished with feet in vast numbers all along its body, 

 like a centipede. The occurrence of annelides is im- 

 portant, on account of their character and status in the 

 animal kingdom. They are red-blooded and hermaphro- 

 dite, and form a link of connexion between the annulosa 

 (white-ljlooded worms) and a humble class of the verte- 

 brata."^ The Wenlock limestone is most remarkable, 

 amongst all the rocks of the Silurian system, for organic 

 remains. Many slabs of it are wholly composed of corals, 

 shells, and trilobites, held together by shale. It contains 

 many genera of crinoidea and polyj^iaria, and there is 

 little reason to doubt that some beds of it are wholly the 

 production of the latter creatures, or are, in other words, 

 coral i-eefs transformed by heat and pressure into rocks. 

 Kemains of fishes, of a very minute size, have been 

 detected by Mr. Phillips in the Aymestry limestone, being 

 apparently the first examples of vertebrated animals 

 which breathed upon our planet. In the upper Ludlow 

 rocks, remains of six genera of obscure character have 

 Ijeen foi- a longer period known. 



The traces of f uci in this system are all but sufiicient to 

 allow of a distinction of genera. In some parts of North 

 America, extensive though thin beds of them have been 

 found. A distinguished French geologist, M. Brogniart, 

 has shown that all existing marine plants are classifiable 

 with regard to the zones of climate ; some being fitted 

 for the torrid zone, some for the temperate, some for the 

 frigid. And he establishes that the fuci of these early 

 rocks speak of a torrid climate, although they may be 

 * Sudi as ami)liioxus anil myxeno (lamprey.^). 



