WHTTE CHALK COMPARED WITH CALCAREOUS OOZE. 
535 
and this remark applies not only to the whole of England, but to 
large parts of northern France also, as may be gathered from the 
descriptions of M. L. Cayeux. (Op. cit.) 
In the Upper Chalk Spheres are abundant in the zone of Holaster 
planus , but they decrease in number through that of Micr. cortes- 
tudinarium. In the higher zones they are much less numerous, 
though generally present. Mr. Hill informs me that it is often 
difficult to sav whether the spherical bodies one sees in a slide of 
chalk are really Spheres or single foraminiferal cells (seep. 501); 
he believes, however, that in most cases both are present. Some 
samples from the same zone contain a larger number than others, 
but he thinks that above the zone of M. cortestudinarium such cells 
and Spheres together seldom make up more than 15 per cent, of 
the recognisable ingredients of the chalk. 
With respect to the occurrence of Spheres in recent calcareous 
oozes, we are unable at present to make a definite statement. 
Minute spherical bodies do exist in many examples of ooze, and some 
are figured on Plate xi. of the Challenger Report on Oceanic Depo¬ 
sits, but Mr. Hill is inclined to regal’d these as foraminiferal cells, 
and he has not seen any which quite correspond with the Spheres 
of the chalk. 
Shell-fragments are another important constituent of some parts 
of the Chalk formation, and under this head Ave include fragments 
of the shells of Mollusca and Brachiopoda, of the zoaria of Bryozoa, 
of the tests and spines of Echinoderms, and of the ossicles of Starfish 
and Crinoids. Of all these organisms Lamellibranch Mollusca, and 
especially the genus Inoceramus , have contributed the largest 
quantity of fragments, and this is only what might have been 
expected from the frequency with which more or less perfect shells 
of that genus occur throughout the Chalk. 
As in the case of Spheres, but to a still greater extent, the quantity 
of shell-fragments varies greatly in different parts of the Middle 
and Upper Chalk ; at some horizons the chalk is full of them, 
while at others they are practically absent. In the zone of Rhyn- 
chonella Cuvieri they are always conspicuously abundant, and are 
fairly so in the loAver part of the Terebratulina zone, but become 
fewer and fewer in the higher part. In the zone of Holaster planus 
they are again very numerous, but above that their numbers 
once more decrease till in the zone of Micr aster coranguinum there 
are generally very feAV, though locally there are layers or bands in 
which such fragments are abundant. In the upper part of the 
M . coranguinum zone, and in the zones of Marsupites and of Actino- 
camax quadratus there are fewer shell-fragments than in any other 
part of the Chalk, that is to say, there are feAver fragments of the 
size we are now considering, and especially of Inoceramus-prisms. 
With regard to the zone of Belemnitella mucronata, Mr. 
Hill finds that in such specimens as he has examined shell-frag- 
pients are decidedly more numerous than they are in the central 
