12 



HARDWICKE'S SCIENCE-GOSSIP. 



OUR COMMON BRITISH FOSSILS, AND 

 WHERE TO FIND THEM. 



By J. E. Taylor, F.G.S., &c. 



No. X. 



A FOURTH division of those well-known stony 

 objects called corals, is that termed Per- 

 forata. These are the familiar twig-like branched 

 corals, whose surface breaks out here and there 

 into flower-like calyces, and whose tips usually 

 terminate in the same sort of objects. The entire 

 structure is distinguished by its light and porous 



Fig. 6. — Recent Arborescent Coral (Oculina axillaris). 



character, whence the name of the group. In spite 

 of their apparent fragility, we find them living amid 

 the most violent of seas, for their rapidity of growth 

 enables them to withstand the destructive effects 

 which would otherwise break them up. The division 

 Aporosa did not make its appearance in the primeval 

 seas, but is first observed in those of the secondary 

 period, although its species are most abundant in the 

 present epoch. The Perforata, however, are repre- 

 sented among primary fossils by both Silurian and 

 Devonian genera, such as Protarea and Pleurodictyum. 

 Perhaps the Perforata are better known by their 

 common name of Madrepores. 



The intervening spaces in the branched or arbores- 

 cent corals, between where one flower-like calyx is 

 seen and another, is called the Ccenenchyma. They 

 are the equivalents of the "inter-nodal spaces" or 

 the distances which separate leaves from one another 

 in the branches of a tree. It is the rapid porous 

 growth of this part which enables such compound 



corals to stand against a good deal of marine wear- 

 and-tear. It is this part, also, which binds the 

 various corallites together into one colony. In deep- 

 sea corals this Ccenenchyma rarely, and perhaps 



Fig. 7. — Astra-a 7-oiulosa, a recent West Indian Coral. 



Fig. 8. — Astrtia favosa, a recent East Indian Coral. 



JlSSSi^ 



Fig. 9. — Astraa ananas, a fossil Cora', common in the upper 

 Silurian and Devonian Limestones. 



never exists, as a means of rendering them compound, 

 but a different method of "compounding" takes 

 place. Oculina (fig. 6) is said by Professor Owen 

 to be the only large coral now found in the north, 

 although our British rocks, especially the Carboni- 

 ferous limestone, are in places almost entirely com- 



