22 PALEONTOLOGY 



the earliest seas, and were perhaps more widely diffused and 

 individually abundant in the Silurian age than at any subse- 

 quent period. " Reef-building " corals are now confined to 

 warm seas, and are wanting even on great tracts of tropical 

 coast. The Oculina is the only large coral now found in the 

 north. But in palaeozoic times the representatives of the 

 modern Astrseas and Caryophyllias extended as far northward 

 as Arctic voyagers have penetrated ; and at a much later 

 period they formed reefs of considerable thickness and extent 

 in the area of the coralline oolite. The Silurian limestone of 

 Wenlock Edge is itself a coral reef thirty miles in length ; 

 and the Plymouth limestone and carboniferous limestone have 

 frequently the aspect of coral-banks skirting the older regions 

 of Cambrian slate and Devonian " killas." The structure of 

 coral-banks may be studied in the lofty limestone cliffs of 

 Cheddar, and in the wave-worn shores of Lough Erne, as well 

 as in the upheaved coral islands of the southern seas. In the 

 fields about Steeple-Ashton, every stone turned up by the 

 plough is a coral ; and our inland quarries and chalk-pits 

 afford to the palaeontologist materials for the study of a class 

 almost wholly wanting on the present sea-shores of Europe. 

 The history of the British fossil corals, as given by Milne 

 Edwards and Haime in the " Monographs of the Palaeonto- 

 graphical Society," exhibits, equally with that of the fossil 

 shells by other authors, a transition from a state very different 

 from that which now subsists in our part of the world, and 

 ;i gradual approximation to the present order of things. 



In the paheozoic strata the corals belong chiefly to two 

 extinct orders ; those of the secondary period more resemble 

 living corals of warmer climates than ours ; and the few ter- 

 tiary genera and species resemble those of Southern Europe 

 and our own coast. 



The distinction between one large group of the palaeozoic 

 Actinoida (CyaiJwjphyttidce) and more modem corals consists 



