DISXEIBUTION OP CORALS. 251 



Cretaceous reefs of Maestricht, Faxoe, and the neiglibourhood of 

 St. Petersburg, and by the limited vestiges of such which still 

 mark the Eocene deposits of the typical English basin. The reefs 

 of the Eocene period find their greatest extension in Southern 

 Europe — from the northern flanks of the Alps and Pyrenees south- 

 ward, and eastward through the Crimea, Egypt, Syria, Arabia, and 

 East India. The more extensive European reefs of the Oligocene 

 period are those of Oberburg, in Styria, and Northern Italy (Crosara, 

 Castel Gomberto, &c.); Miocene reef-patches still exist in Spain, 

 Southeastern Prance, Northern Italy (Superga), the Vienna basin, 

 and Hungary, the larger structures, however, occurring in the region 

 farther to the south (Malta, Asia Minor, the West Indies, Java). 

 At the close of this period the reefs appear to have still further 

 receded, and in the Pliocene they completely vacated the present 

 continental area. Dr. Duncan has remarked the existence in the 

 Table Cape Tertiaries of Tasmania (Miocene ?) of reef-building 

 corals (IleUastraea, Thamnastraea) at a point removed some fifteen 

 degrees of latitude south of the coral isotherm of that region." 



The limited range in depth — not exceeding twenty fathoms — of 

 reef-building corals is certainly extraordinary, and something that 

 still remains in the nature of a puzzle to the naturalist. That it is 

 not, either wholly or in great part, dependent upon conditions of 

 temperature is conclusively proved by the total absence of such 

 organisms in depths beyond one hundred and twenty feet where a 

 temperature considerably' above that required for coral growth still 

 prevails (Pacific Ocean, Red Sea). Possibly a movement, or want 

 of movement, in the oceanic waters has something to do with this 

 abrupt limitation. 



The Alcyonaria or Octocoralla, except in so far as some of the 

 forms until recently classed with the Tabulata may be considered 

 to belong to this group— as Halysitea and Syringopora, supposed 

 to be allied to the organ-pipe (Tubipora), Heliolites to Heliopora — 

 acquire but little geological importance. The pennatulids appear 

 to have one or more representatives (Pavonaria) extending back to 

 the Cretaceous period, and a limited number (Graphularia ?) also m 

 the Eocene. The sea-fans (Gorgonid89), whose brilliantly coloured 

 masses constitute such a striking feature of the coral patches of 

 both the Atlantic and Pacific oceans, are not positively known be- 

 fore the Miocene period (Primnoa, Gorgonella). The genus Isis 



