FORMATION OF OOLITE. 17 
On some of the islets connected with the Australian barrier, 
there are beach-deposits that contain true oolitic grains, as 
described by Jukes. 
He mentions a stone " made up of small round grains, some of them 
apparently rolled bits of coral and shell, but many of them evidently con- 
cretionary, having concentric coats. It was not unlike some varieties of 
oolite in texture and appearance . . . Some parts of it made a very 
fair building-stone, but it got softer below, till it passed downwards into 
a coarser coral sand, unconsolidated and falling to pieces on being- 
touched . . . many recent shells, more or less perfect, were found 
compacted in the stone, and one or two nests of turtle eggs were dis- 
covered . . . It is evident from the fossil turtle eggs, that the con- 
solidation of the stone had taken place after it was raised above the sea. 
It was due, probably to the infiltration of the rain water percolating 
through the calcareous sand, that had been gradually piled above high- 
water mark by the combined action of the winds and waves."* 
These facts are of especial interest when we note the occurrence 
of Reptilian eggs in the Great Oolite of Cirencester. 
Moreover it is stated that while the beach is often composed of coarse 
fragments of worn corals and shells, hardened beds not infrequently stand 
out above high-water mark to a height of 6 or 8 feet, and at angles of 
6 or 8.f 
Dana mentions that the " sand-rock " is sometimes drifted into hillocks 
or ridges by the winds, and afterwards consolidated, and this rock is more 
or less friable, and frequently oolitic. Captain R. J. Nelson observed 
the same features in the Bahamas, where the "calcareous sand " is heaped 
up irregularly by the wind, so as to produce false-bedding. Dana 
remarked that some of the beach-deposits become cemented by being alter- 
nately moistened and dried, through the action of the recurring tides and 
the wash of the sea on the shores. " The waters take up some carbonate of 
lime, and this is deposited and hardens among the particles on the evapo- 
ration of the moisture at the retreat of the tides. In some places the 
grains are loosely coherent, and seem to be united only by the few points 
in contact ; and with a little care the calcareous coating which caused 
the union may be distinctly traced out. In other cases, the sand has 
been consolidated into a solid limestone rock, the interstices having been 
filled till a compact mass was formed. Generally even the most solid 
varieties show evidence of a sand origin, and in this they differ from the 
reef rock ... In most localities the rock is an oolite or oolitic lime- 
stone. The grains become coated by the agglutinating carbonate of lime, 
and each enlarges thus into a minute sphere a spherical concretion ; and 
the aggregation of these concretions makes the oolite ... At certain 
localities the beach sand-rock has been washed away after it was formed ; 
and occasionally large masses or slabs have been uplifted by the sea and 
thrown high up on the beach . . . Deposits of the same kind some- 
times include detritus from the hills. "|| 
It is a study of these sedimentary and other accumulations, due 
to the destruction of Coral-reefs, that will help to explain the origin 
of our oolitic deposits. The reefs themselves forming fringes or 
barriers along the coast are more or less solid beds of limestone, 
presenting an unstratified appearance, attaining in places a ccm- 
* Voyage of the " Fly," vol. i. pp. 127, 128, 340. 
t Jukes, op. cit. pp. 1-3. 
J; Corals and Coral Islands, 1872, pp. 154-156. 
Quart. Journ. Geol. Soc., vol. ix. p. 206. 
i| Dana, Corals and Coral Islands, pp. 152, 153, 348. 
E 75928. 
