306 THE CRETACEOUS ROCKS OF BRITAIN. 
from near Warminster, in the amount of shell-fragments and 
“ spheres,” but mineral and glauconitic grains are fewer in num¬ 
ber, and the former smaller. About 20 feet higher shell-fragments 
decrease, while mineral grains and glauconite, though com¬ 
paratively rare, are to be seen high in the zone. “Spheres” are 
common, hardly abundant, but Foraminifera increase decidedly, 
though as a rule the individuals are not large and the area occupied 
by their tests is relatively small. Grlobigeimia and Textularia 
are the prominent forms. Still higher the chalk is chiefly amor¬ 
phous material, recognisable particles rarely forming more than 
10 per cent, of the rock, but just under the Belemnite Marl, shell- 
fragments, Foraminifera and “ spheres ” increase again. 
Bucks., Beds., and Herts.— In these counties {see Analyses 38 and 
39) the chalk of the zone of Holaster subglobosus varies but little 
in structure. The lower part, just above the Totternhoe Stone, 
contains many finely-divided shell-fragments, “ spheres,” with a 
few Foraminifera, but mineral grains cannot often be recognised 
more than 20 feet above the base, while grains of glauconite are 
rare. Above this the chalk chiefly consists of amorphous 
calcareous material, with few shell-fragments, Foraminifera, or 
“ spheres.” (See Plate V., Fig. 2.) 
The general character of the zone is, however, not infrequently 
broken by seams of more shelly chalk, and occasionally by beds 
which have marked characters of their own. Thus at Chalk- 
shire (South of Wendover) there is a bed of hard gritty chalk 
locally called the Rag, and again at Ivinghoe (46) and Sundon 
beds of similar character are exposed at the same horizon. The 
deposit consists largely of comminuted shell-fragments, coarser 
and more unevenly assorted than in the Totternhoe Stone, with 
but little fine material. Foraminifera are fairly common, but 
the abundance of fish teeth and scales, fragments of bone, and 
small ovoid coprolites give a marked character to the bed. 
The larger calcareo-phosphatic green-coated nodules which abound 
in the Rag have a structure identical with that of the grey chalk. 
Most of the nodules seem pierced by boring Molluscs, and the holes 
are now filled usually with coarse shelly material of the Rag, but 
sometimes with fine amorphous material. 
Analysis of the material of this bed (see page 317) does not show 
any very exceptional difference to the chalk of the zone in this 
locality, but there are more coarse particles, the percentage of these 
being higher than the average. They consist chiefly of lumps 
of green mud (see page 312), sand being in small proportion. The 
Foraminifera are of the usual type— Rhizammina, Tritaxia, Buli- 
mina and G-audryina. Of the last genus, however, there is a new 
species or variety. 
Between Totternhoe and Royston the upper part of the zone 
contains more “ spheres,” and shell-fragments and just under the 
Belemnite Marl both become very numerous. A feature now 
