E. Wethered—Structure of Jurassic Pisolite. 197 
particles approach the size of a pea or bean, the rock is termed 
Pisolite, Pisolitic Limestone, or Pea-grit.” 
The Coralline Pisolite. 
For the specimens which I have examined from the Coralline 
Oolite and for information descriptive of the beds, I am indebted to 
Mr. H. B. Woodward, F.G.S., to whom I return my cordial thanks. 
The first specimens sent me were collected at Osmington, near 
Weymouth, from a bed 1 foot thick, and oceurring 6 or 7 feet 
from the base of the Coralline division, named “Osmington Oolite”’ 
by Blake and Hudleston.! The specimens consisted of dark brown 
calcareous spherules about the size of peas. They were loosely em- 
bedded in an argillaceous matrix in which there were also oolitic 
granules of the ordinary size and type. 
The sections of the spherules show a nucleus in each, but the 
structure of the surrounding material can only be studied through 
a microscope. Viewed through a low power the nucleus is observed 
to be enclosed by rudely concentric layers of innumerable minute 
tubuli. Examined by a half-inch object glass the tubuli are clearly 
defined. They measure about z;'s5 of an inch in diameter, and 
are remarkable for the extraordinary vermiform twistings and 
turnings which they exhibit, Fig. 9, Pl. VI. They appear to make 
up the whole mass; no skeleton fibre can be made out, and what 
spaces there are between the tubuli are filled with crystalline calcite. 
The only system exhibited by the tubuli, if system it can be called, 
is that they appear in aggregations, having a concentric tendency 
around an unoccupied space in the centre of each aggregation, and 
that the latter seem to interlace one with the other. The other 
specimens sent me by Mr. Woodward were collected at Sturminster 
Newton, from the bed No. 6a. mentioned by Blake and Hudleston.? 
The horizon is the same as ‘the Osmington pisolite, and the bed is 
described as consisting of “loose pisolite of large flattened concre- 
tions, 1 foot thick.” In shape and size the spherules are similar to 
those from Osmington, but they are lighter in colour. The micro- 
scopic structure is generally well preserved and coincides with the 
description given of the Osmington pisolite. 
Pisolite, or Pea-grit, from the Inferior Oolite. Pl. VI. Fig. 8. 
After examining the specimens of pisolite from the Coralline Oolite 
I turned to the Pea-grit, so well known as occurring at the bottom 
of the Inferiar Oolite in the Northern Cotteswolds. The greatest 
development is in the neighbourhood of Cheltenham, and the strati- 
graphical features of these interesting beds have been frequently 
referred to by geologists; among whom I may mention Sir R. 
Murchison, Mr. Strickland, Dr. Wright, Professor Hull, Mr. Lycett, 
Professor Buckman, Mr. Witchell, Mr. Etheridge and Mr. Lucy. 
1 Quart. Journ. Geol. Soc. vol. xxxili. p. 265. 
* Loc. cit. p. 276. 
