82 OUR COMMON BRITISH FOSSILS. 



fossils is Favosites fibrosus, perhaps the oldest known 

 British species, and one of the widest distributed of 

 all Silurian corals. Many varieties of it are known, and 

 among others one which is seen encrusting univalve 

 shells as if it had destroyed them, after the fashion 

 which is still practised by some mechanically parasitic 

 zoophytes in modern seas. The stone walls on and 

 about breezy Applethwaite Common are often full of 

 small kinds of fossil corals, as impressions of Cyatho- 

 phylhim, Favosites, Heliolites, etc. 



The Caradoc rocks contain by far the largest 

 number of species of fossil corals of any of the older 

 Palaeozoic rocks, about forty-two different kinds 

 having been described. One remarkable fact concern- 

 ing these ancient corals is that we often find one 

 genus represented by only one species. This is par- 

 ticularly the case in the Upper Llandovery rocks, 

 where, out of sixteen genera of fossil corals, no fewer 

 than eleven have only one species each. 



A very rich development of corals seems to have 

 taken place during the period when the Upper 

 Silurian and Middle Devonian limestones were de- 

 posited. No fewer than seventy-six species have 

 been obtained from the Wenlock rocks of Great 

 Britain alone ; whilst from the Devonian strata fifty- 

 two species have been catalogued. The Carboniferous 

 limestone, however, appears to have been deposited 

 when the ancient coral fauna had reached its 

 greatest development, for one hundred and forty-one 



