HARDWICKE'S SCIENCE-GOSSIP. 



13 



posed of corals, both reef-building, deep-sea, and 

 shore-loving species. 



There is often a difficulty in at once saying which 

 of the fossil corals were "reef-builders," and which 

 were not. For it does not follow that because the 

 fossil corals are of a compound character they were 

 therefore engaged in the work of reef- building. Per- 

 haps the safest plan is to trace the existing genera of 



Fig. 10. — Litliostrotion basaltifortnc, an abundant compound 

 rugose Coral in the Carboniferous limestone. — The lighter 

 parts show the transverse structure, as seen when the coral is 

 cut for sections. 



Fig. 11. — Vertical section of Litliostrotion Phillipsii, showing 

 structure. 



reef-builders, as far back in geological time as we 

 can, or at any rate to compare the fossil kinds with 

 their nearest living representatives. Few genera are 

 more distinctively " reef-builders " than the Astnea, 

 whose characteristic star-like arrangement of polypes 

 or corallites (the latter often so close together that 

 they press each other into oval or polygonal shapes), 

 has given to this genus its distinctive name. The 



wide-spread geographical distribution of the genus 

 Astrrea, and the fact that it is engaged in areas separated 

 by such enormous distances in reef-building, would 

 be an incidental proof to a geologist of its geological 

 antiquity, even if this genus were not found in our 

 upper Silurian and Devonian limestones. Thus Astraa 

 rotulosa (fig. 7) is a living species of this interesting 



Fig. 



-Clisiophyllum, a single coral, characteristic of the 

 Carboniferous limestone formation. 



Fig. 13. — Transverse section of CHsiophyllum, showing 

 (in part) details of structure. 



genus of corals found abundantly in West Indian seas r 

 where it is both met with in coral-reefs, and masking 

 and adhering to natural rocks. Astrcca favosa (fig. 8),. 

 on the other hand, is peculiar to the East Indian 

 seas, where it is hardly less abundant. And Astma 

 ananas (fig. 9) is a common fossil in the Silurian 

 limestone at the Wren's Nest, Dudley, in the formation 

 of which we can hardly doubt that it and its compeers- 



