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THE CRETACEOUS ROCKS OF BRITAIN. 
The change already noted in the zone of A. varians of the facies 
of the Microzoa in the north-west of Norfolk and northwards is 
reflected in the Totternhoe Stone. 
Rhizammina , Reophax, Haplophragmium, Ammodiscus, and 
Trochammina, all represented in North-west Norfolk and Speeton, 
were not observed in the examination of the Arlesey specimen. The 
specimens of Bulimina and Gaudryina are, as usual, smaller in the 
north than in the south. 
Ostrcicoda.— The valves of Ostraeods were fairly numerous in the 
Arlesey specimen. The following were isolated from the washings, 
and were namedtby Mr. Chapman ‘.—Cythereis triplicata (Roem.) 
and C. Ornamentissima (Reuss), Gytheridea perforata (Roem.), and 
Gytherella obovata (J. and H.). 
In the Totternhoe Stone of Heacham they were less numerous. 
Examination of the Residues. 
Detrital Minerals. — Besides quartz and mica no other minerals 
have been definitely recognised in the Totternhoe Stone; their 
proportion of the coarse residue is small, the sandy nature 
of the stone being due to comminuted shell-fragments and 
not to mineral grains. In size they do not exceed those of 
the over or underlying Chalk, though the Heacham specimen con¬ 
tained a few grains which were larger than usual. 
Secondary Minerals. — Glauconite. —"This mineral occurs plenti¬ 
fully in the Totternhoe Stone of Arlesey and Heacham. It is 
generally of a pale green colour; many of the grains are small 
and rounded, but there are also many in the form of foramini- 
feral casts. 
Marcasite. — Bright brassy spherules and small irregular masses 
of this mineral occurred in the Arlesey specimen, accompanied by 
masses of iron oxide, possibly derived from the oxidisation of this 
material. 
Tabulation of Results. 
The appended table gives the results of the treatment with the 
aoid solution of four specimens of the Chalk at this horizon:— 
i 
