298 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
The rock closely resembles beds of proved Upper Cretaceous age, similarly 
overlying Oxfordian shales in the south of Scalpay, and at Strollamus and 
Strathaird in Skye.” 
Desiring to compare the structure of the Belhelvie boulders with the 
Cretaceous rocks above mentioned, at the kind request of Professor Judd 
five thin sections and a hand specimen were courteously sent me by Professor 
Watts from the School of Science, South Kensington ; and my friend Mr 
Jukes-Browne was able to send me hand specimens and slides both from 
the glauconite base and siliceous rock from Eigg, which had been kindly 
sent by Mr Clough, and several slides of that found in Skye at Scalpay 
and Strollamus. 
The sections of the siliceous chalk discovered by Professor J udd have 
already been described by Professor Rupert Jones in an appendix to 
Professor Judd’s paper,^' but for purposes of comparison a little more detail 
may be given of those sent me. 
To save repetition it may be said that the ground mass of all these 
specimens is minutely crystalline silica. 
0 3 . — Siliceous Chalk, Beinn-y-Hattan. Described by Professor Rupert 
Jones as “ Inoceramus chalk.” This section contains a large number of 
Inoceramus prisms, the characters of which are fairly well preserved ; as a 
whole they are similar to those of the Upper Chalk. Though somewhat 
obscured in the now silicified material of the matrix, it is possible to 
trace the outlines of F oraminif era ; Glohigerina, Bulimina, Dentalina, 
and Planorhulina have been recognised by Professor Rupert Jones, but 
he does not mention sponge spicules which occur in many parts of the 
section. In my opinion casts of Radiolaria occur also, and I have 
noticed two well-preserved Xanthidia. It is impossible to estimate the 
relative proportions of the recognisable organisms of which this rock 
originally consisted. Shell fragments were the dominating ingredient, 
with Foraminifera and sponge spicules. There are patches of colloid silica 
in globular form. 
In the section from the specimen (O 3) sent me by Professor Watts, 
the general features are the same. Inoceramus prisms are exceedingly 
numerous, and there are many Foraminifera. Sponge spicules are also 
present, but globular colloid silica occurs in great quantity, partly as clear 
globules and partly opaque. 
As colloid silica in globular form will be frequently mentioned, it will 
be well to describe its appearance in the silicified chalks. 
* “Notes on the Foraminifera and other Organisms in the Chalk of the Hebrides,” 
Q.J.G.S., vol. xxxiv, 1878, p. 739. 
