1914-15.] Structure of the Chalk in the West of Scotland. 301 
spicules ; but they are present, and the rock must have been once permeated 
with colloid silica. 
O 5, Beinn-y-Hattan, seems to have been a purely foraminiferal ooze. 
There are a few spicules in it, but several species of Foraminifera are 
clearly, if faintly, outlined in the now siliceous matrix, while not a 
few are casts in an opaque mineral (? once glauconite). Glohigerina is the 
predominating form. 
Thus both at Beinn-y-Hattan and at Carsaig the evidence points to a 
passage from a deposit containing a proportion of terrigenous matter to a 
purer calcareous ooze. 
The whitish calcareous sandstone with chalky inclusions and siliceous 
patches and nodules of the Isle of Eigg. In the hand specimen it is seen 
that some of the nodules are bordered by lighter material, suggestive of 
the rind of flint ; others have no such border. They are distributed 
irregularly through the sandstone, are of rounded or sub-angular contour, 
and vary in size from about an inch in the longest diameter to small specks. 
The material surrounding the nodules is quartz sand, the grains being 
about I mm. in average size, but some are 5 or 6 mm. and more in greatest 
length. The material cementing the grains is largely chalcedonic; but 
calcareous matter is included, for there is a decided reaction with hydro- 
chloric acid. Some of the nodules give a slight reaction ; in others it is 
not perceptible. 
From the hand specimen I had two slices cut, and Mr Jukes-Browne 
sent me two others (T 4602, T 4603), belonging to the Geological Survey 
of England, and three small hand specimens were kindly sent me from the 
same source. 
T 4603. — This is a section through one of the dark nodules and the 
sandstone. The ground mass of the nodule is minutely crystalline 
chalcedony, organisms being vaguely indicated by coarser crystals. Though 
somewhat obscure, as a whole there is no difficulty in tracing the outline 
of Foraminifera and foraminiferal cells in all parts of the nodule; they 
include Glohigerina, Textularia, and two or three Rotaline forms. 
Inoceramus prisms are fairly common, and there is one fragment showing 
the prismatic structure of the shell. Sponge spicules are present, but not 
very numerous. There is evidence that colloid silica in globular form 
occurred in this nodule. 
T 4602. — Section through a nodule. The organisms in this section are 
rather more obscure than in the preceding, but Glohigerina outlined some- 
times by a brownish filtration occur with some regularity in all parts of 
it. There are but few Inoceramus prisms : they have merged in the 
