of Edinburgh, Session 1864 - 65 . 
Pentland Hills, the Upper Silurian beds 
pass upward into certain red conglomerates | 
O y 
and sandstones, which are supposed to he ^ % 
the base of the Lower Old Eed Sandstone. $ 
This same lower member of the formation ^ 
occurs in the east of Berwickshire, where it S 
consists, to a large extent, of volcanic ash and < 
conglomerate, but it has yielded fragments 
of Pterygotus and plants.* The Ochil Hills 
are formed of a series of felspathic lava-beds, 
with interstratifications of sandstone and 
volcanic conglomerate, the whole belonging 
to the Lower Old Eed Sandstone. The struc- 
ture of the hills, as made out by the Survey, 
is shown in the subjoined sketch (fig. l).f 
The middle division of the Old Eed Sand- 
stone is seen in the chain of the Pentland 
Hills, where it consists of a mass of coarse 
conglomerate and grit, overlaid with a great 
thickness of felspathic lava-form and ashy 
rocks. It lies on the worn edges of the 
Upper Silurian and of the red-coloured strata, 
which are supposed to indicate the bottom 
of the Lower Old Eed Sandstone. Ho fossils 
have yet been detected in any part of it, so 
that no means exist of deciding how far S 
it represents the great Caithness flagstone 
series. On the denuded ends of the rocks 
of this central group come the conglomerates 
and sandstones of the upper division, which 
pass upward into the Carboniferous system. 
In the accompanying diagram across the 
Cairn Hills in the Pentland Chain, the gene- 
^ See “ The Geology of Eastern Berwickshire,” 
Mem. Geol. Survey, p. 27. 
t This section combines in a generalised form 
the result of the survey made in concert by my 
colleagues. Dr John Young, Mr James Geikie, Mr 
B. N. Peach, and myself. 
-Sketch-section across the Ochil Hills. 
