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remarkable concretionary character. This character has been 
noticed first in the beds at Kellaway, and elsewhere Lyeu 
describes the rock as being lenticular. He further speaks of it 
as an arenaceous limestone, which would hardly apply to the 
beds at South Cerney. 
A clean section of certain portions of the rock shows a series 
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of concentric shells more or less regular in form, the central 
mass varying in shape from a sphere to prolate spheroids and 
ellipsoids. These central masses vary very much in size, 
and the successive eccentric shells vary in thickness, and are 
sometimes marked off one from another by a different coloration 
of the stone. I have taken several measurements of these 
eoncretionary masses. Here is one of the largest, an elipsoid :— 
ft. in 
Longest diameter ies see tag 2 
Diameter of central mass BR oh ys 
Thickness of first shell... sro Ol coe: 
3 5, Outer ,, ... aes Fa O08 8 
The line of junction between the central mass and the first 
shell, as well as between that and the outer one, was very clearly 
indicated by the varying colours of the stones near to the junc- 
tion, a deep reddish brown line varying from 4 in. to 2 in. in 
_ width, evidently coloured by iron, marking it out. 
q Thave had made a determination of the specific gravities of 
pieces of the rock taken from the centre of one of these blocks, 
j and from the junction of the first shell and its included core. 
The result shows that the latter is of a higher specific gravity 
than the central portion, the respective determinations being 
9-4 and 2:7. This may be explained, as I have suggested, by 
_ the greater amount of iron contained in the dark coloured 
_ portions. That the successive layers lying without the central 
mass are comparable to the layers of a shell is very clearly 
_ proved by the fact that on the weathering of broken masses the 
central core in many places separates out, and the successive 
shells do the same. Lying about in the cutting were numbers 
¥ of these regular shaped cores, called “cannon balls” by the 
_ workmen, who put aside for me three or four of those which 
- nearly approached a true spherical form. Furthermore, the 
