56 



OUR COMMON BRITISH FOSSILS. 



not meet with them where the sea-water is cooler than 

 62°, and therefore the sub-tropical belts of our globe 

 now roughly comprehend their distribution. But we 

 find fossil corals of all kinds — simple, compound, and 

 reef-building. They are characteristic of many thick 

 limestone formations, from the Silurian upwards. We 

 have in the British Islands abundance of fossil reef- 

 building corals, where their modern representatives 

 could not now live. What climatal changes these 



Fig. 34.— A, Deudrophyllia, a compound Coral ; B, CaryoJ>hyllia, a recent Coral. 



valuable fossils indicate ! Not less important are the 

 conditions of the ancient seas they lay before us. We 

 carry our minds back to a period when there were coral 

 islands, fringing-reefs, and barrier-reefs in British seas. 

 These reefs also tell the geologist of the adjacency 

 of land, and inform him of the fact that the sea-floor 

 was in a state of subsidence. 



Moreover, few fossils are prettier, more easily pro- 

 curable, or look better in the cabinet, than corals. 



