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172 



RELICS OF PRIMEVAL LIFE 





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Laiircntian fossil. The first analo<jy which sug- 

 gested itself to Sir W. Logan, and a very natural 

 one, was that to the so-called layer-corals (Figs. 43 

 to 45) that abound in the Silurian, Ordovician, and 

 Cambrian rocks, and which though undoubtedly 



Fig. 43. —Stromatocerium rugosum^ Hall, Ordovician. 



fossil animals, have proved very difficult to inter- 

 pret or to assign to any known group. At first 

 vaguely associated with the true corals, they were 

 subsequently regarded as probably of more simple 

 character, and as gigantic Protozoa ; and later 



