271 
1914-15.] Chalk Boulders from Aberdeen, etc. 
minute shot, though some are ovoid in shape.^ They are especially 
abundant in the lower part of the Middle Chalk of England, and may 
be separated in quantity by levigation. The cells ” are usually ovoid, but 
their outline is irregular, one side being often flattened. They are some- 
what larger than “spheres,” and measure occasionally as much as 1*8 mm. 
in their longest diameter. The old definition of the unicellular bodies found 
in the chalk as “primordial cells of Glohigerina or other Foraminifera ” 
could be applied perhaps not inaptly to those “ cells.” 
B 2. — The matrix of this rock is crowded with prisms of Inoceramus 
shell and sponge spicules. A few well-marked Glohigerina and one or two 
other species occur together with other foraminiferal cells, some “ spheres,” 
and Radiolaria. The Inoceramus prisms seem to be of a long narrow type, 
but the condition of the matrix tends in some degree to obscure their 
contour and character. Though a large part of the matrix can be seen to 
consist of minute calcitic particles, the rock is permeated with colloid silica, 
some of which, especially in the neighbourhood of the spicules, is in a 
minutely globular form, and the silica in the walls of many of the spicules 
shows the progress of the molecular change from the amorphous to the 
globular condition, while in others it has reached the crystalline form 
of chalcedony. Many of the cells of the Foraminifera are also filled with 
this mineral. 
The rock failed to break down in the 20 per cent, solution of hydro- 
chloric acid, and though a quantity was kept in it for some days, even then 
all the lime had not been removed. From the residue thus obtained the 
larger and presumably chalky pieces were separated by sifting, and the 
remainder was slightly treated with heated caustic potash in the hope of 
freeing some of the organisms. On attempting to separate the heavy from 
the lighter portions by levigation, it was found that the heavy part 
consisted almost entirely of small lumps of white material. Most of these 
were cavernous and perforated by circular holes, obviously the casts of 
spicules. On breaking, they were found to consist of the siliceous casts of 
small Foraminifera, cells, “ spheres,” fragments of spicules and silicihed shell, 
an occasional Radiolarian, minute spherical bodies or globules of clear silica 
which sometimes occurred in small aggregations, and irregular masses of 
amorphous material which, when viewed by direct light, was of a snow- 
white colour. 
This amorphous material (the “ ciment ” of M. Cayeux) in which the 
more definite forms are embedded, when mounted in balsam and viewed 
with transmitted light, seems to have for its foundation clear structureless 
* “ The Cretaceous Rocks of Britain,” Mem. of the Geol. Survey., vol. ii, 1903, p. 500. 
