ON THE BRITISH FOSSIL CORALS. 



165 



pied a large portion of the region now constituting the soil of modern 

 Europe ; and that the bed of the Jurassic sea was a slowly subsiding area of 

 great extent, like many parts of the Coral Sea in the Indo-Pacific Ocean of 

 our day"*. 



The restriction of species to very definite areas, and to limited zones amongst 

 these succeeding coral-reefs, is veiy remarkable, and, as was noticed to occur 

 in the Lias, the corals are occasionally persistent, and are associated -with 

 different moUuscan species. But the physico-geological changes which pro- 

 duced new reefs must have been preceded by considerable geographical changes, 

 for, as a rule, the species of the grand divisions of the Jurassic system are 

 different. Thecosmilia Wrightl of the lower reef of the Inferior Oolite has 

 considerable resemblance to the ThecosmiU.ce of the Inferior Lias ; but no 

 Liassic species pass upwards into the Oolites. Only four species are com- 

 mon to the Inferior and Great Oolites, and one to the Coral Rag and Great 

 Oolite ; yet there was a succession of the physico-geographical conditions 

 favourable for the formation of reefs on the same area. The existence of 

 reefs in so high a latitude during the Oolitic period, and their formation by 

 polypes whose genera were all extinct during the early Cainozoic period, but 

 which are clearly represented by allied genera in the existing reefs, are very 

 suggestive. These were the last reefs of the British area ; for there are no 

 traces of agglomeration of reef-building genera in the Lower Greensand, the 

 Gault, Upper Greensand, Chalk, or Tertiary formations. The nearest approach 

 to a reef must have been in the Lower Oligocene period, when the Tabulate 

 corals and Solenastrcett of Brockenhurst formed a small outlier of the European 

 coral sea of the time between the Nummulitic age and the lowest Falunian 

 deposits. 



The succession of reefs and deep-sea or littoral coral conditions appears 

 to have been as follows on the British area south of Yorkshire, after the 

 termination of the Permian period : — 



Triassic No corals (dry land). 



Rhaetic Few corals. Littoral and deep water, from 



5 to 200 fathoms, 



"i C Zone of Amm. planorbis . . Scattered reefs and littoral corals. 



'^ \ „ angulatus . . Barrier reefs and deep-water corals. 



^q I „ Bucklandi . Scattered reefs and deep-water corals. 



Middle Lias No reefs. Littoral and deep-water corals. 



Upper Lias No reefs. Littoral and deep-water corals. 



Inferior Oolite Successive reefs. 



Great Oolite Successive reefs. 



Coral Rag Reefs. 



Portland Oolite Reefs rare. No other corals. 



Lower Greensand Littoral and deep-sea corals. No reefs. 



Gault Littoral and deep-sea corals. No reefs. 



Red Chalk Littoral and deep-sea corals. No reefs. 



Upper Greensand Littoral corals. No reefs f. 



Lower and Upper Chalk Deep-sea corals. Few littoral corals. 



Eocene Deep-sea corals. No reefs. Littoral corals. 



Lower Oligocene Deep-sea corals. Scattered reefs. Lit- 

 toral corals. 



Crag Deep-sea corals. No reefs. Littoral corals. 



Recent Deep-sea corals. No reefs. Littoral corals. 



* Dr. Wright, op. cif. t Deep-sea and small reefs in the west. 



