FROM THE OOLITIC STRATA. 13 



" One quarry, near Ayton. which may be considered as a type of the others, consisted 

 of masses of crystalline coralline limestone, the beds having an irregular undulating 

 appearance. The corals appear to have grown in areas of depression of the coralline sea ; 

 the rock consists of large masses of highly crystalline limestone, forming nodulated 

 eminences and concave curves, in beds of from twelve to eighteen inches in thickness, 

 having a stratum of yellowish clay filling up the hollows, and forming a horizontal line 

 again to the stratification ; then follows another stratum of crystalline limestone, which 

 assumes the same nodulated condition as the one below it, the surface of the coral masses, 

 where exposed, showing that the whole is almost entirely composed of a small-celled 

 Astraa, Thamnastrcea concinna, Goldf. (T/i. micraston, Phillips), in some altered condition ; 

 the reef is exposed to about ten feet in section, and rests on another, forming the floor of 

 the quarry, and which descends many feet deeper. The corals are bored by Gastrochance, 

 and numerous shells were seen imbedded in the coral mass, which had nestled in the 

 crannies of the reef." 



Dr. Wright sums up with regard to the French, German, and British strata of the 

 JEtage Corallien as follows : — 



" From this general view of the geographical distribution of the Coralline Zone, it 

 would appear that this formation was composed of a series of coral-reefs in the Jurassic 

 sea, which, during the period of their construction, occupied 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." 1 



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

 succeeding coral-reefs, is very remarkable, and, as was noticed to occur in the Lias, the 

 corals are occasionally persistent, and are associated with different molluscan species. 

 But the physico-geological changes which produced 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 Wrighti of the lower reef of the Inferior 

 Oolite has considerable resemblance to the Thecosmilia of the Inferior Lias ; but no Liassic 

 species pass upAvards into the Oolites. Only four species are common 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 favorable 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 



1 Dr. Wright, op. cit. 



