LOWER CHALK—MiGROGRAPHlC STRUCTURE* 
283 
cent, of it. Here and there are large quartz grains perhaps 
derived from the underlying Eed Chalk; glauconite is rare. A 
single rod-like sponge spicule and a fragment of Hexaetinellid 
mesh is seen in one of the slides. 
The Inoceramus-Bed (21) is practically a shell-sand, consisting 
chiefly of Inoceramus-prisms (entire or broken) with fragments of 
the shell itself showing the prismatic structure. Foraminifera are 
common; G-lobigerina, Textularia, and various forms of Rotalina 
can be distinguished. Small grains of glauconite are present, and 
this mineral can be seen infilling the tests of the Foraminifera. 
The whole is cemented by fine granular crystalline calcite. 
A slide of the Chalk midway between the Inoceramus Bed and 
the Totternhoe Stone (22) shows the coarse ingredients of the rock 
to be “ spheres,” with wdiich are numerous Foraminifera. Many of 
the latter are probably arenaceous forms, but Globigerina can be 
recognised, and somewhat coarse shell-fragments are conspicuous. 
The actual area occupied by recognisable organisms is not more 
than 25 per cent, of the wdiole rock. The shell-fragments occur 
very irregularly or in patches, some parts of the sections being full 
of them, in other parts they are absent. No glauconite or other 
mineral grains are visible in the slides. 
Lincolnshire and Yorkshire.— The aspect of thin sections from 
the Am. varians zone in these counties is similar to that of Hunstan¬ 
ton. In general aspect the Sponge Bed continues nearly the same 
through Lincolnshire, but in Yorkshire it becomes inseparable from 
the Red Chalk. The Inoceramus-Bed can be followed through 
Lincolnshire and Yorkshire ; the specimens examined differ but 
little from that of Hunstanton, except perhaps that the 
shell-fragments are more irregular in their distribution and even 
coarser in the more northern examples. 
In the higher beds shell-fragments show the same curious 
irregularity, occurring either in patches or in thin veins which 
may extend across a thin section of the rock. Nearly all may be 
referred to Inoceramus-shell. Of the Foraminifera Globigerince 
are sufficiently common to form a distinctive feature, species of 
Textularia and Rotalina are not of infrequent occurrence, while a 
coiled test (probably Ammodiscus ) can be often made out. The 
proportion of Foraminifera to the mass of the rock continues to be 
very small. 
In many specimens from Yorkshire and Lincolnshire, and in a 
few from North-west Norfolk, there occur ill-defined spheres which 
bear a strong resemblance to the tests of Radiolaria, but their cha¬ 
racters are so much obliterated that it is not possible to speak posi¬ 
tively. The most abundant form is similar to that figured in 
Q.J.G.S. Yol. li. Plate xxii., Fig. 1. Sponge-spicules are of rare 
occurrence. 
