Chap. XI.] 
OLD EED SANDSTONE OF SCOTLAND. 
249 
interbedded felspathic rocks, extend south-westwards towards the source of 
the Nith. In the valley of the Irvine, at Lanfine, it consists of a grey mi- 
caceous flagstone, with trappean conglomerates and felspathic traps, and it 
! has there yielded some fine specimens of Cephalaspis Lyellii. The Ochil 
Hills belong to this same lower division. They contain a thick series of 
coarse trappean conglomerates and ashy beds, with enormous sheets of 
porphyritic and amygdaloidal felspathic trap. They pass under a set of 
red sandstones containing Parka decipiens *. It is these trappean rocks 
which in a great anticlinal arch are prolonged into the chain of the Sidlaw 
! Hills of Forfarshire. In the east of Berwickshire, near Eeston, a group 
of very ashy sandstones and conglomerates is overlain unconformably by 
the Upper Old Red Sandstone of the Merse. They have yielded fragments 
of plants and Pterygotus, and are probably referable to the Lower Old 
Eed Sandstone f . 
" b. The middle group is one which I have only recently detected, and of 
which I do not yet know fully the relations. Perhaps it may eventually 
prove to belong in part to the Lower Old Red series. In the Pentland Hills 
it consists of dull greenish sandstones, greywackes, and conglomerates, with 
ashy beds and very thick sheets of various felspathic rocks, the whole series 
reaching a thickness of many thousand feet. As shown in the accompanying 
section, it rests (c, cl) unconformably upon highly inclined Upper Silurian 
W. Sketch Section across the South End of the Pentland Hills. E. 
East Cairn Hills. Carlops. 
e e hb a c d g f 
a. Upper Silurian shales, sandstones, &c. b. Eed sandstones and conglomerates, 
possibly marking the base of the Lower Old Eed Sandstone, c. Thick conglomerates 
and grits forming here a Middle division of the Old Eed Sandstone, d. Felspathic 
lava-beds interstratified with c. e. Upper Old Eed Sandstone. /. Carboniferous sand- 
stones, shales, &c. g. Intrusive greenstone coming up along a line of fault, h. Fault. 
(See also page 159.) 
shales (a), and on the red beds which may there represent the base of the 
Lower Old Red Sandstone (b). Traced south-westward, this series seemed 
to me likewise to overlap unconformably the Lower Old Red conglome- 
rates and sandstones of the Tinto district. It is covered unconformably 
by the Upper Old Red Sandstones, the junctions being well seen to the 
south-west of the Pentland range. It thus appears to be a series inter- 
mediate between the upper and the lower zone of the Old Red Sandstone, 
from each of which it is separated by an unconformity. No fossils have 
yet been found in it in this region ; so that it cannot be linked by organic 
remains with the middle series of the North of Scotland, to which, of course, 
* The structure of the eastern half of the Ochil given hy Mr. Geikie in the Proceedings of the 
chain has been mapped in detail for the Geological Royal Society of Edinburgh, vol. v. p. 350. 
Survey by Mr. H. H. Howell, Mr. G-eikie, Dr. t They are described by Mr. Geikie in the Me- 
Young, Mr. James Geikie, and Mr. B. N. Peach, moir on Eastern Berwickshire, Mem. Geol. Sur- 
A section to explain the structure of the hills was vey, 1864, chap. iv. 
