P ® 
VAR 
\ 
EL. Neaverson—Foraminifera of the Hartwell Clay. 457 
are relatively rare, probably owing to the abundance of selenite. 
Ossicles of Isocrinus were found here. 
Long Crendon—Abundant quartz and frequent grains of 
glauconite, but the latter is not so common here as at localities 
nearer Aylesbury. Ostracods rare, Foraminifera commen. 
Wheatley and Shotover Hill—Highest “ Kimmeridge Clay ”— 
Quartz grains and small aggregates of marcasite are abundant ; 
glauconite grains occur, but are not common. Foraminifera 
abundant, ostracods common. Blue clay above nodule band. 
Quartz grains and small concretions of marcasite are the commonest 
minerals, whilst glauconite is rare. Foraminifera and ostracods 
are common. 
Speaking generally, the colour of the glauconite of the Hartwell 
Clay is a rich green, but many grains present a dull yellowish 
appearance. This yellow colour appears to be due to decomposition, 
as on boiling with dilute hydrochloric acid the grains become green. 
The size of the grains is variable, some glauconite being present 
in each grade-size separated by elutriation, but they do not occur 
in grades greater than 0°5 mm. diameter, which consist entirely of 
shell fragments. Exact determinations of the specific gravity of 
the glauconite have not yet been made, but it is certainly variable. 
While most of the glauconite has a specific gravity less than 2°8, 
many grains come down with the heavy detrital minerals separated 
in bromoform. The grains are usually rounded, but some are sub- 
angular ; many are obviously casts of Foraminifera and occasionally 
broken specimens of Cristellaria have been seen to contain an 
infilling of glauconite. 
This indicates that, although some of the glauconite may be 
detrital, much is indigenous to the deposit. Similar observations 
have been made on the glauconite in the Gault of Ford, near 
Aylesbury, mentioned on a later page. In some samples of the Hart- 
well Clay, marcasite is most abundant, glauconite being rare. 
The marcasite occurs as spherical concretions or irregular grains, and 
often as an infilling in tests of Foraminifera. It would seem that in 
these cases marcasite has been formed instead of glauconite. It is 
hoped that more detailed work will show whether these two minerals 
are connected in any way ; for the present no generalization can be 
made. 
THE FORAMINIFERA. 
In the following notes the occurrence of the Foraminifera at the 
localities mentioned is indicated by letters, thus :— 
V.r. == very rare. . I to 2 specimens 
r. = rare : 5) BGO) &) ny 
f. = frequent . - 6 to 10 53 pin 1 lb. of clay. 
ec. = common . . 10 to 20 a 
a. = abundant . above 20 Hf ] 
