EOLIAN LIMESTONES 



577 



on Gaysum Island, or of Foraminifera, as on the southern side of 

 Gaysum Island, where Orbit olites complanata is the predominant 

 form. 



Older Examples. Some of the Jurassic oolites of Great Britain 

 appear also to belong in the category of wind-drifted calcareous 

 sands. De la Beche (3) figures a pronounced cross-bedding struc- 

 ture of the Forest marble (oolite) of Somersetshire, here repro- 

 duced. (Fig. 121.) The diagonal layers are "composed of broken 

 shells, fish teeth, pieces of wood and oolitic grains, sometimes mere 

 rounded pieces of shells, the various substances lying in the planes 

 of the diagonal layers, and presenting every appearance of having 

 been shoved or pushed over the more horizontal surfaces formed 



Figs. 122a and b. Cross-bedding of uniform-grained St. Louis limestone (cal- 

 carenyte), south of St. Louis, Mo. Scale i -.2$. 



during the intervals between the mud deposits." The cross-bed- 

 ding is rather more regular than that of wind deposits generally, 

 and suggests the torrential type. De la Beche states that the Bath 

 oolite of Somersetshire is likewise of this type, the rounded frag- 

 ments being drifted together with the true oolite grains. Accord- 

 ing to Evans (14:^80), the grains of the Great Oolite often show a 

 worn character, suggesting abrasion by the wind, and he holds that 

 the false-bedded oolites which succeed the Stonesfield slates are not 

 improbably of eolian origin. Personal examination of a number of 

 these British oolites has convinced the author of their remarkable 

 resemblance to wind-drifted sands. The cross-bedding figured 

 above (Fig. 122), from the Mississippic calcarenytes of Missouri, 

 also suggests an anemoclastic origin for at least a portion of this 

 rock. 



Possible application to the chalk beds. The remarkable com- 

 position and the structural characters of the White Chalk of west- 

 ern Europe have commonly arrested attention and given rise to 

 speculation regarding its origin and mode of deposition. At first 

 it was thought that the deep-sea Globigerina ooze forms a modern 

 analogue of this deposit, but when it was found that the foraminif- 

 era! shells composing the chalk were very largely of shallow-water 



