328 THE CRETACEOUS ROCKS OF BRITAIN. 
but become distinctly scarcer towards the summit of this division. 
Nothing is easier than to wash a sample of soft Chalk Marl and 
obtain many species and varieties not only of arenaceous Foramini¬ 
fera, but also of those with porcellanous and vitreous tests. But 
sections of the rock never convey the idea of abundance, and 
none will compare in profusion of Foraminifera with those draw¬ 
ings of sections of Globigerina and other oozes published in the 
Challenger Report on Deep Sea Deposits. (Plates XI., XII., XIII.) 
In fact, many sections of the higher part of the Holaster subglo- 
bosus zone seem almost devoid of Foraminifera. In the finest 
part of the chalk pieces of broken foraminiferal tests are common, 
but they are far outnumbered by calcareous particles and crystals 
which give no clue to their derivation. 
Taking all things into consideration, the amount of material 
which these minute forms contribute to the formation of the Lov er 
Chalk cannot anywhere exceed 20 per cent., even if foraminiferal 
“ cells ” are included ; it is usually less than this. 
In this estimation, however, “ spheres ” are excluded. In some 
localities these are extremely abundant, and when estimated by 
the area they seem to occupy in a thin section, sometimes form more 
than half of it. It must be recollected, however, that they are all 
tilled with amorphous (sometimes crystalline) material, and the 
actual amount which the cells themselves contribute to the deposit 
is smaller than appears. 
The greater number of the species of Foraminifera which occur 
in this division of the Chalk range upward from the Gault; it 
should be stated, however, that these investigations have extended 
the upward range of many species. Of the 148 species and 
varieties identified in this division of the Chalk 102 are recorded 
in the Gault by Mr. Chapman*, twenty-seven are not recorded, 
and nineteen specie! and varieties are new to science. 
On the whole in those parts of the Lower Chalk which are 
most purely calcareous, and where the quantity of recognisable 
particles exceeds that oi the finer material, it may be said that 
particles of broken shells, and especially of Lamellibranch shells, 
are the chief constituent; next in relative quantity are the 
calcareous bodies which we have called “ spheres,” and thirdly 
Foraminifera ; but at some horizons the spheres and Foraminifera 
combined form a larger proportion of the mass than the shell- 
fragments. 
It should, however, be borne in mind, that though in the pre¬ 
ceding pages prominence has been given to the definite grains 
and particles which can be separated from the matrix, yet inmost 
samples of Lower Chalk the greater part of the mass consists of 
what has been classed as “ finest material,” and that it is only at 
certain horizons (as in the Totternhoe Stone) that the quantity of 
recognisable particles exceeds that of this fine material in bulk. 
* Foraminifera of the Gault of Folkestone. By F. Chapman. Journ. 
Boy. Micr. Sue. (1893). 
