198 E. Wethered—Structure of Jurassic Pisolite. 
Dr. Wright! divided the beds as they occur at Leckhampton 
near Cheltenham as follows, in descending order : 
“A. Brown, coarse, rubbly oolite, full of flattened concretions, cemented 
together by a calcareous matrix. aa L2ereet 
‘©B. A hard cream-coloured pisolite rock made up ‘of flattened concretions 
of about the thickness of those in A... soo KO) 
*¢C. A coarse, brown, ferruginous rock composed ‘of large oolitic grains 20 
Total ee ... 42 feet’’ 
Commencing the microscopic examination at the beds marked 
C by Dr. Wright, we see a limestone made up of granules and 
fragments of organisms, the spaces between being filled in with 
crystalline calcite. The organic fragments consist of spines of 
Kehini, Polyzoa, Crinoids, shells of Mollusca and Foraminifera, 
those of the Crinoids and Hchini are by far the most numerous. 
All the granules show a nucleus, but in some instances the original has 
become converted into crystalline calcite. The nuclei vary, indeed 
all the fragmentary remains of organisms mentioned as occurring in 
the rock may be said to serve. When the nucleus is a portion of a 
spine, then the shape is less spherical and is somewhat elongated. 
The granules are of two types; first the true oolitic granule 
distinguished by the concentric layers; second, spherules which 
vary in size from that of ordinary oolitic granules to that of a pea. 
In this latter type of spherule the nucleus is not surrounded by 
concentric layers of carbonate of lime, but by vermiform tubuli 
averaging about 53> of an inch in diameter (Figs. 10-11), but in 
some instances they are larger. The tubuli may be said to be 
arranged in layers or bands which are concentric with the nucleus. 
In some instances the tubes turn and twist about in a very remark- 
able manner, sometimes assuming a flat spiral form. 
Passing to the succeeding series of beds, marked B by Dr. 
Wright, we find the pisolite spherules? as large as peas (Fig. 8, 
Plate VI.), but often flattened. The typical Pea-grit is confined to 
one bed which averages about 4 feet 6 inches thick, and is best 
studied at Cleeve Hill. It is a mass of the spherules, which are 
firmly cemented in the matrix. On exposure to the action of the 
atmosphere the matrix is removed and the spherules then stand out 
in relief and after a time become detached. On examining some of 
these with a magnifying glass a vermiform structure may be noticed 
In some instances. 
Thin sections made from this typical bed show the nucleus in the 
spherules to be surrounded by the same tubuli as represented in 
Figs. 10 and 11, but if anything they are more vermiform. Some 
of these spherules, however, show layers and spaces not occupied 
by that type of tubuli, and when these are not filled with crystal- 
line material, minute tubuli are seen which correspond with those in 
the pisolite from the Coralline Oolite. 
? Quart. Journ. Geol. Soc. vol. xvi. p. 7, 1860. 
' * T use the term spherule for the pisolites and granule for the ordinary oolitic 
orms. 
