1914-15.] Structure of the Chalk in the West of Scotland. 303 
times with ragged outlines, and from this size they diminish to smaller 
particles of which the rock is full. Fragments of Bryozoa also occur. 
Foraminifera, though not abundant, are in some variety. Globigerina, 
Textularia (two species), several Rotaline forms, and a Nodosarian occur. 
Sponge spicules are common, their walls are replaced by calcite. 
Highest Cretaceous limestone, just beneath Eocene beds, Strollamus, 
Skye. This is a finely granular crystalline limestone in which the forms 
of all organisms are nearly lost. The angular prisms of Inoceramus can, 
however, still be traced, and there are a few fragments of Echinoid plates. 
Here and there the outline of single foraminiferal cells are just discernible. 
There are no sponge spicules, but in a second section there are traces of two 
or three. 
Chert in mudstone overlying Cretaceous limestone, Belach Ban, Scalpay 
(two specimens). In one of these sections the traces of Foraminifera are 
rare, but there are a few Inoceramus prisms. Spicules can be seen, though 
not commonly, but 1 am of opinion that Badiolaria occur. 
In the other (from the base of the mudstone), while in some parts 
organisms are obscure, other parts are obviously a pseudomorph of a 
calcareous ooze. Globigerina, Textularians, Rotaline forms, with cells and 
spheres are well marked. Some are casts in opaque material. There are 
but few traces of spicules. 
Little can be said of the highest Cretaceous limestone of Strollamus, 
Skye. It is now a finely granular calcite limestone in which are faint 
traces of Inoceramus prisms, foraminiferal cells, and fragments of Echinoid 
plates, there being no traces of siliceous organisms or terrigenous material. 
The section of Cretaceous limestone from a volcanic neck, Brodick Bay, 
Isle of Arran, seems also a pure chalk. The character of the shell 
fragments, the presence of Bryozoa, the fact that the walls of the spicules 
are replaced by calcite, together with the absence of any trace of silica in 
globular form, or terrigenous material, shows that it must have once been a 
purely calcareous ooze. Horse-shoe forms occur in this chalk. 
Both the specimens seem to me to be of a higher horizon than any of 
those previously described, and they suggest that there may have existed 
in the West of Scotland Cretaceous strata of greater thickness than any 
yet discovered. 
The two specimens of chert from the mudstone and the base of the 
mudstone at Scalpay yield no evidence of interest ; both doubtless belong 
to the Cretaceous series. 
I do not propose to discuss the changes which have taken place in the 
Cretaceous rocks of the West of Scotland, wrought probably by the heat 
