265 
LOWER CHALK—MICROGRAPHIC STRUCTURE. 
area in the section, while calcareous “spheres”* are very abun¬ 
dant, and occupy, at least one-third of it. No satisfactory 
section could be made of the specimen from Maiden Bradley. 
The basement-bed at Lulworth (3a) also consists largely of 
amorphous material with many “ spheres ” ; the rock is also fuU 
of small pieces of shell and a few larger fragments; several of the 
latter are evidently derived from the plates of an Echinoderm. A 
few Foraminifera and grains of quartz and of glauconite are 
scattered through the rock. 
In a specimen from the top of the glauconitic marl of Mupe 
Bay (3b), sand grains are an important feature of the deposit, 
and glauconitic grains are also numerous. The proportion of 
coarse shell fragments is also large: many of these are long and 
thin and give no clue to their derivation, others are Inoceramus- 
prisms and not a few are derived from Echinoderms. Large 
Foraminifera, chiefly Textularia, are common. These coarse 
materials are irregularly scattered through the amorphous matrix, 
many of the longer shell fragments have their long axes in the 
same plane, and the aspect of the whole section suggests current 
action. 
The Chloritic Marl of Ventnor (4) has a similar calcareous 
matrix ; the mineral grains are hardly so prominent as in the Book- 
ham example, but glauconite is more abundant. Large, coarse 
shell fragments, chiefly Inoceramus-iprmms and Foraminifera, occupy 
half the area of the section, but “ spheres ” are very scarce. 
The Folkestone (5) specimen is a glauconitic sand, the interspaces 
between the grains being now filled with finely granular crystalline 
calcite, once probably a calcareous mud. Certain areas of small 
size—seen in a hand specimen as whitish marks or pipings—are 
filled with fine amorphous calcareous material to the exclusion of 
the larger glauconitic grains. In such areas “ spheres ” can be seen, 
and Foraminifera can be detected in other parts of the slide lying 
between the grains of glauconite. 
The aspect of a thin section of the Cambridge Greensand (6) 
viewed under the microscope with a 1-inch objective, is that of an 
evenly-grained, sandy, and rather calcareous mud, containing large 
grains of glauconite. 
The ground mass appears as brownish-grey amorphous matter, 
largely inorganic, but under crossed Nicols it can be seen to 
contain caleitic particles, and through this are thickly scattered 
minute mineral grains ; Foraminifera occur here and there and it 
is possible to pick out occasionally a fragment'of- a' tooth or bone, 
probably fish remains. Few shell-fragments can be seen. The 
grains of glauconite are nearly all of large size and though gener¬ 
ally distributed through the mass occur also thickly packed in 
streaks or veins, the interstices being filled up with the amorphous 
matter and the minute sand grains. 
* For a description of these spheres see under Middle Chalk, p. 500» 
