16 LOWER OOLITIC ROCKS OF ENGLAND : 
Some of the granular limestones in the Lower Purbeck Beds 
contain organic fragments, with a thin coating that shows con- 
centric and radiate structure ; and they also comprise more or 
less rounded pellets, often similarly coated, and showing obscure 
resemblances to " Girvanella "-structure. 
In some instances, as pointed out by Lycett, Polyzoa are found 
adhering to the pisolites ;* and I have found Serpulae and small 
Oysters attached to them at Crickley. 
Witchell has remarked that " The passage of fragments of shell, 
and other particles of which the nuclei consist, along a sea bottom 
covered with a calcareous muddy deposit, portions of which 
became attached to the moving fragments as they were carried 
onward, might account for the concentric layers which compose 
the pisolites."t He notes also the occurrence of oolite grains, as 
well as rounded fragments of limestone and organic remains in 
the Pea Grit. 
Again Messrs. Blake and Hudleston, in referring to the 
Corallian pisolite of Norih Dorsetshire, remark that the beds 
" seem to indicate that they are the result of irregular currents 
bringing material that had been rolled about for some time in a 
calcareous ooze."J 
The facts favour this general explanation of the formation of the 
pisolitic limestones; while the influence of incrusting organisms 
may have played a part in their production. It is, however, not 
unlikely, as lately suggested by Mr. 0. Reid, that the filaments of 
Algae, attached to tiny pebbles, assisted in the deposition of cal- 
careous matter, and to the subsequent decay of these filaments 
may be due tho tiny tubes of the so-called Qirvanclla.^ 
Origin of Oolite and of strata associated tvith Oolitic limestones. 
In considering the origin of oolite we have first to inquire 
whether similar accumulations are now in process of formation. 
Fitton in 1835 remarked on the many points of resemblance 
between the top beds of the Portland series and the recent agglo- 
merated limestones of Bermuda and the shores of Australia. || As 
pointed out previously, the resemblances between such limestones 
and the characteristic oolites are mostly superficial. 
Specimens of recent limestones from St. Helena, Bermuda, and 
Bahama, as remarked by Dr. Sorby, consist largely of rounded 
grains of Corallines, Corals, Balani, and Mollusca, together with 
Foraminifera ; while others show the organic structure but imper- 
fectly preserved or so crystallized with the mud that their 
structure and outline have been 
* Cotteswold Hills, p. 38. 
t Geology of Stroud, p. 44 ; Proc. Cottesw. Club, vol. viii. p. 35. 
j Quart. Jourii. Geol. Soc., vol. xxxiii. p. 278. 
See remarks at meeting of Geol. Boc., Mar. 8, 1893 ; Quart. Journ. Geol. Soc., 
vol. xlix. (Proc.), p. 143. 
|| Proc. Geol. Soc., vol. ii. p. 186. See also E. J. Nelson, Trans. Geol. Soc., 
ser. 2, vol. v. p. 103. 
^ Address to Geol. Soc., 1879 ; Quart. Journ. Geol. Soc., vol. xxxv. (Proc.), p. 74. 
