CHAP. XXI 
ERUPTIONS NORTH OF THE GRAMPIANS 
343 
to this part of the country, so that we shall before long be in possession 
of more detailed inforinatiou regarding the character and sequence of its 
volcanic history and the geological age of the eruptions. 
Mr. H. Kynaston, who has begun the mapping of the eastern portion 
of the district, finds that there, as further west, the bottom of the volcanic 
series is generally a breccia or conglomerate. He has met with two leading 
types among the lavas, the more aliundant being strongly vesicular, the 
other more compact. He has observed also numerous dykes and sills of 
intrusive porphyrite, trending in a general N.K.E. and S.S.W. direction, and 
pointing towards the great granite mass of Ben Cruachan.' 
Mr. E. G. Symes has traced the volcanic series to the north and south 
of Oban. While visiting with him part of his ground, I was much struck 
with the evidence of an intrusive mass at the base of the volcanic series in 
the Sound of Kerrera. A prominent feature on the east side of the channel, 
known as Hun Uabairtich and 270 feet high, consists of andesite which 
appears to combine both a central boss and a sill. The rock breaks through 
the black slates and the overlying conglomerates and sandstones, and has 
wedged itself into the unconformahle junction between the two formations. 
It is beautifully columnar on its sea-covered face, some of the columns 
being 120 feet or more in length, and gently curved. 
“LAKE ORCADIE 
We now cross the whole lireadth of the Scottish Highlands in order to 
peruse the records of another of the great detached water-basins of the Old 
Eed Sandstone, which for the sake of brevity of reference I have named and 
described as “ Lake Orcadie ” (Map 1.). Tliis area has its southern limits 
along the base of the hills that enclose the wide Moray Firth. It spreads 
northward over the Orkney and much of tlie Shetland Islands, but its bound- 
aries in tliat direction are lost under the sea. In the extensive sheet of 
water which spread over all that northern region the peculiar Caithness Flags, 
with their associated sandstones and conglomerate.s, were deposited to a total 
depth of 16,000 feet. A sigillaroid and lycopodiaceous vegetation flourished 
on the surrounding land, together with ferns, Psilo])hyton and conifers. The 
waters teemed with fishes of which many genera and species ha\e now 
been described. The remains of these creatures lie crowded upon each 
other in the flagstones in such a manner as to indicate that from time to 
time vast quantities of fish were suddenly killed. Xot impossibly, these 
destructions may have been connected with the volcanic activity which has 
now to be described. 
In the year 1878 I called attention to the evidence for the existence of 
contemporaneous volcanic rocks in the Old Eed Sandstone north of the range 
of the Grampians, and specially noted three localities where this evidence 
could be seen — Strathbogie, Buckie and Shetland.^ Since that time Messrs. 
1 Ann. Report Oeol. (Surv. (1890), p. 29 of reprint. 
- Trans. Roy. Soe. EcUn. xxviii. (1878). 
