269 
1914-15.] Chalk Boulders from Aberdeen, etc. 
of magnesia contained in the rock. The amount insoluble in the acid is 
then given. This is called the residue, and is separated into two parts 
by levigation, the fine and coarse residues, and the estimated amount of 
soluble silica is also given. In the following columns are details of the 
composition of the coarse residue. 
These specimens differ from each other in some important particulars, 
and at the risk of some repetition I feel compelled to describe them fully. 
Specimens from the Glacial Drift of Aberdeenshire. 
A 9. — A rounded nodule of greenish-grey friable rock the size of a 
small potato. Small particles of similar material, sometimes containing 
small nests of sponge spicules, occur associated with the chalk boulders 
in the boulder clay. Viewed as a thin section under the microscope 
with a one-inch objective, this rock was seen to consist of grains with 
rounded contour, some of them being opaque, while others displayed 
a green colour. Mineral grains were also abundant, amongst which 
quartz and mica could be recognised. The remainder was more or less 
fine inorganic matter which filled the interstices between the grains and 
slightly separated them. 
The rock gave no reaction with the 20 per cent, solution of hydro- 
chloric acid and did not break down without pressure. By levigation 
rather more than 40 per cent, of the finest matter was removed. The 
remainder was found to be made up of definite forms and small irregularly 
shaped masses of dark grey material, grains of glauconite including a few 
short rod-like lengths, the casts of spicular canals, and mineral grains. 
Many of the definite forms mentioned above were apparently the casts 
of some organism. They were cone-shaped and seemed built up of the 
casts of successive chambers diminishing in size towards the apex of the 
cone. These casts were sometimes in a greenish mineral akin to glauconite, 
but not infrequently in grey mud, sufficiently hard to resist considerable 
pressure with a needle. I believe them to be casts of Kadiolarians, for 
they closely resemble both in shape and size undoubted casts of those 
organisms in silica found in other boulders. I have submitted these casts 
to Dr G. J. Hinde, F.R.S., who says there is a very strong resemblance in 
general form to genuine Radiolariee and little difference in point of size, 
so that one can hardly avoid the conclusion that they may be casts of 
Dictyomitra. Casts in mud and glauconite of other forms occur, probably 
of Foraminifera, but they give little clue to their identification. 
The masses of dark grey material in the heavy residue seem to 
