FORMATION OF OOLITIC STRATA. 21 
along the coast-line, for the heavy surf is confined to the outer 
reefs. On this outer side were accumulated the sediments due to 
the wear and tear of the reefs, and the oolitic granules that were 
formed by chemical agency. In drawing these conclusions we 
cannot however argue that reefs of similar character and magnitude 
existed in Oolitic times : we can only infer that the general condi- 
tions were similar.* 
Hence, although Coral-reefs played an important part in the 
history of the Oolites, the larger reefs that may have existed must 
have been destroyed by the agents that laid down the successive 
deposits. These notions receive support when we notice in the 
Oolites themselves, evidences of reconstruction, and the occurrence 
of small rolled masses of previously formed oolite in later 
accumulations.- 
The growth of reef -building Corals at the present day is dependent on 
the temperature of the surface-waters, and the presence of currents that 
keep up the food-supply, as well as on the purity of the water. They 
nourish only in comparatively shallow water. As Dana has remarked, 
the " Facts seem to indicate though perhaps not sufficient to demonstrate 
that the Gulf Stream has had, from the Jurassic period in Geological 
history onward, the same kind of influence on the temperature of the 
North Atlantic Ocean which it now has."f 
While many of the Jurassic Mollusca belong to genera that 
have a wide range, most of their living representatives taken 
together suggest a warm if not tropical character, and very many 
of them are such as now exist in association with coral-reefs. 
Among these are Nautilus, Anomia, Area, Astarte, Avicula, 
Cardium, Cucull&a, Cypricardia, Lima, Modiola, Ostrca, Pecten, 
Bnlla, Cerithium, Delphinula, Natica, Nerita, Patella, ' Phasianella,' 
Pleurotomaria, Pterocera, Rostellaria, Solarium, Trochus, and 
Turbo. Polyzoa, Serpulae, Echinoderms,Foraminifera, and Sponges 
are likewise abundant in the neighbourhood of reefs. 
Fossils of the Oolitic Series. 
The assemblages of fossils met with in each division are found 
to vary according to the sedimentary conditions. Thus the 
organic remains of the purer false-bedded oolites or " freestones " 
differ from those of the more earthy and more slowly deposited 
" ragstones."| In successive deposits of similar nature there is 
some repetition in the forms of life. Thus Terebratula maxillata 
abundant in the purer marly limestone of the Inferior Oolite 
(Oolite Marl) occurs plentifully in rocks of similar lithological 
character in the Great Oolite; in the Colly weston Slate and 
Stonesfield Slate there are some identical species ; and long ago 
Prof. Buckman compared the fauna of the ragstones of the 
* See descriptions by Jukes, Voyage of the " Fly," vol. i. pp. 332, 333, 343. 
In early geological times, reefs of more extensive character may have existed. See 
Dana, op. eit. p. 353. See also Tomes, Quart. Jouru. Geol. Soc., vol. xl. p. 354. 
t Dana, op. cit. p. 362 ; Duncan, Rep. Brit. Assoc. for 1869, p. 166. 
j Hull, Geol. Cheltenham, p. 61 Quart. Jouru. Geol. Soc.,' vol. yvi. p. 72; see 
also Judd, Geol. Rutland, &c., p. 49. 
