264 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Rocks of Cretaceous age and apparently in situ have only been found 
at a few localities on the western coasts of Scotland. The first of these 
was discovered by Professor J udd ^ at Morvern by the shore of Loch Aline, 
and also in the Island of Mull. A small patch was discovered by Mr David 
Tait on the Island of Eigg in the course of his work for the Geological 
Survey, and another on the Isle of Skye.f 
In 1898 Messrs Jukes-Browne and Milne, in the Geological Magazine, 
made a report on the Cretaceous fossils found at Moorseat, Aberdeenshire J — 
all these will be referred to again in the sequel. 
In 1908 Mr David Tait § recorded the occurrence of Cretaceous fossils 
near Leavad, Caithness. The fossils, which include Craspedites, Hamites, 
and Crioceras, were found in a hard concretionary sandstone which may 
possibly be in situ.\\ 
The methods employed in the examination of the boulders were similar 
to those used by me in the examination of the Chalk of England, which 
are given at some length in the memoir on the Cretaceous rocks 
of Britain.^ 
Many of the boulders, however, contained soluble silica, and it became 
necessary to estimate the amount. This was done by first pounding some 
of the chalk (about 10 grams) to a coarse powder, not, however, rubbed to 
impalpable dust. The powder was treated with a 20 per cent, solution of 
hydrochloric acid. When effervescence had subsided, the residue was 
washed with hot water till there was no trace of reaction with nitrate of 
silver in the filtrate. After being thoroughly dried and weighed, the residue 
was treated with a 12 J per cent, standardised solution of caustic potash 
and kept in a water bath just at boiling-point for one hour and a half. 
The solution containing the residue was then diluted with water to five 
or six times its bulk, and just acidulated with hydrochloric acid. The 
liquid was then filtered, and the residue remaining in the filter-paper 
washed as before, dried, and weighed. The amount of soluble silica was 
estimated in the difference between the weight of the residue after treat- 
ment with acid and that after treatment with potash. The question of 
* “On the Secondary Eocks of Scotland,” Q.J.G.S., vol. xxxiv, 1878, p. 728. 
t “ The Geology of the Small Isles of Inverness-shire,” Memoir of the Geological Survey 
(Scotland, sheet 60), 1908, pp. 33-34. 
I Geological Magazine, Dec, 4, vol, v, 1898, p. 21. 
§ “ On the Occurrence of Cretaceous Fossils in Caithness,” Proc. Edin. Geol. Soc., vol. ix, 
part 4, 1909, ]d. 318. 
II This mass of Cretaceous rocks at Leavad has been proved by boring to rest on shelly 
Eoulder clay. — J. Horne, 
IF “The Cretaceous Eocks of Britain,” Memoir of the Geological Survey, vol. ii, 1903, 
p. 499, etc. 
