PISOLITE. 15 
Inferior Oolite and Coraliian Rocks, of a minute tubular organism 
similar to that previously described from the Lower Silurian 
(Ordovician) Rocks of Ayrshire, under the name of Girvanella 
problemotica by Dr. H. A. Nicholson and Mr. R. Etheridge, jun.* 
The Girvanella has been compared with certain forms of Foraminifera 
described by Dr. H. B. Brady under the names of Syringammina fragilis- 
sima and Hyperammina vagans ; branching organism s/the latter of which 
is found " spreading in irregular tortuous lines over the surface of shells 
or stones, or, in the absence of foreign bodies, growing coiled upon itself 
in irregular rnasses.''f 
It is interesting to note that forms provisionally identified with Girva- 
nella, occur in the oldest fossiliferous rocks, for Mr. C. D. Walcott recog- 
nizes an organism of similar character in the Olcnellus-zonc.^. Whether 
the form is a Sponge, a Rhizopod, or an Alga, is at present uncertain. 
It is interesting to note that in his account of the Bahamas (1852), 
Captain R. J. Nelson remarks that "The marshy lands, that are gradually 
taking the place of the creeks and brackish lakes, abound with, and may 
be said at some points to consist largely of a highly calciferous moss-like 
Conferva"; and he further describes this accumulation " as a spongy 
mass of laterally aggregated and much-interwoven fasciculi of tubes, per- 
haps 7 o" in diameter. " 
In 1890 Mr. Wethered brought forward evidence to show 
that Girvanella-iubea occurred in the true oolitic granules of the 
Inferior Oolite (freestone) at Chedvvorth, and also in the Coralline 
Oolite ; and he maintained that the spherules in question were 
not concretions, but due to a variety of Girvanella the so-called 
pisolitic granules being in his opinion c ' really formed by the 
growth of an organism around a nucleus."|| 
It is admitted that the shape of the pisolites depends upon the 
form of the nucleus, but the tubes of Girvanella appear to be 
plastered around the nuclei and often to be twisted about in a 
very irregular manner ; so that it occurred to both Mr. Teall and 
myself that the Girvanella might have been derived mechanically 
from the calcareous mud of the sea-bed.1[ (See p. 10.) 
Resemblances to " Girvanella "-structure were noticed by Mr. 
Teall in the nucleus of oolitic grains in the Osmington oolite, 
and in the margin as well as in the centre of some of the pisolitic 
concretions from Stovver. (See Plate I., p. 26, fig. 1.) " Gir- 
vanella "-structure was well shown in the pisolite of Sturminster 
Newton, and, in his opinion, mechanical picking up of foreign 
matter must also have played a part in the growth of the pisolite, 
because the grains contain quartz-fragments. The same structure 
appears in the nuclei of some grains from the Great Oolite of 
Farley Down, in pellets in the " Scallett Bed " (Great Oolite) of 
Box, and in the Great Oolite of Calmsden and Rodmarton. 
Obscure " Girvanella "-structure was seen in pisolitic grains from 
the Inferior Oolite of Ancaster. 
* Monograph of the Silurian Fossils of the Girvan District in Ayrshire, vol. i., 
J880, pp. 23, 24, Plate ix., fig. 24; and Nicholson, Geol. Mag., 1888, p. 22. 
f " Challenger" Reports, vol. ix. p. 242, fig. 9. 
j Tenth Ann. Rep. U. S. Geol. Survey, Part 1, p. 598. 
Quart. Journ. Geol. Soc., vol. ix. p. 210. 
|| Quart. Journ. Geol. Soc., vol. xlvi. pp. 175, 276, and 282 ; and vol. xlvii. p. 553. 
|f Ibid., vol. xlvii. p. 570. 
