li DESCRIPTIVE REMARKS. 
Hills, and the tract of hilly country stretching thence by the head 
of Nithsdale into Ayrshire. In the Lesmahago district this group 
of strata rests conformably upon the Upper Silurians, between the basin 
of the Clyde at Lanark and the Ayrshire Coal-fields; fish remains are 
abundant in Forfarshire; Cephalaspis Lyelli and the crustacean Ptery- 
gotus anglicus occur in this group of strata. 
The northern type has also been grouped into three divisions; the 
Upper, consisting of light red and yellow sandstones of Dunnet Head, 
north of Caithness, and the Orkney and Shetland Islands, with plant 
remains, Calamites (?). 
The Middle composed of grey flagstones occasionally calcareous and 
bituminous, covers a large area in Caithness, and extends into the 
Orkney Islands. These beds contain numerous fossil fish, Pterichthys, 
Coccosteus, &c., Estheria, a crustacean, and land plants, Lepidoden- 
dra (?), ferns, &e. 
The Lower, consisting of red sandstones and conglomerates, rests 
unconformably upon the metamorphic rocks of the Highlands, in Ross- 
shire, Sutherland, and Caithness. Pteraspis has been found in these 
beds at Lybster, in Caithness.* 
The Old Red Sandstone of Scotland has been graphically described 
by the late Hugh Miller; this designation, therefore, which, as Sir R. 
Murchison observes, ‘‘ has been thus rendered classical, may well be 
retained as a synonym for the great group of intermediate age between 
the Silurian rocks beneath, and the Carboniferous formation above it, 
which in those countries where it assumes more calcareous, schistose, 
and slaty characters 1s termed Devonian.”’ 
In the south of Ireland, counties of Cork and Kilkenny, a fine 
grained sandstone occurs, which from its fossil contents is considered to 
be an equivalent of the Upper Old Red Sandstone of Scotland. 
The term Devonian is applied in Devonshire to rocks which cover 
a large part of the county, and adjacent districts in Cornwall, consist- 
ing of clay slates (locally called Killas), and grey limestone; these 
strata occupy a similar position between the Silurian and Carboniferous 
formations, although lithologically and paleontologically these deposits 
are unlike the Old Red Sandstone of Hereford, the South Welsh coun- 
ties, and Scotland. 
The late Professor Jukes, in alluding to these strata which contain 
an abundant marine fauna, observes that ‘‘ it is quite possible that the 
slates and limestones of South Devon and the Red Sandstone of South 
Wales, although each deposited within the same great period, are not 
strictly contemporaneous, but were formed at different parts of the 
period ; or it is possible that the Red Sandstone series of South Wales 
is not a continuous series; that the lower part of it, at all events, is 
older than any of the Devon series, while the upper part may be newer 
than much of that series.”’} 
* Jukes and Geikie, Manual of Geology (1872), p. 570. 
t+ Manual of Geology (1862). p. 491. 
