File:The Quarterly journal of the Geological Society of London (12683206275).jpg

1856..
HARKNESS — PERMIAN ROCKS OF SCOTLAND.
261
In the course of the Glasgow and South-western Railway, we
have the sandstones exposed twice in the cutting between the Thorn-
hill and Carron Bridge Stations, and one of these exposures presents
a troughing of the beds. North of Carron Bridge Station, in the
cutting at the south entrance of the Drumlanrig tunnel, we have the
sandstones and accompanying strata well exposed. The beds here
dip south, at an angle of about 1 2° ; and besides sandstones we have
breccias of an interesting character. The south end of the tunnel
consists of amygdaloidal trap ; and on the south side of this we have
the breccias composed of fragments of the igneous rocks in great
abundance ; and these, with the associated sandstones, dip from the
amygdaloids. See Section, fig. 3. At the north end of the tunnel,
Fig. 3. — Section at the South Entrance of Drumlanrig Tunnel,
Carron Bridge Station, Dumfriesshire.
b. Sandstones and Breccias.
a. Trap-rock.
we have variegated Carboniferous grits, dipping S.S.E., at an angle
of 25° ; and through these grits the igneous rock has burst.
The occurrence of igneous rocks here, and the relations which
these bear to the Carboniferous beds, as well as their connexion
with the newer sandstone strata, are subjects of interest, as we are
enabled, to some extent, to derive information concerning the age of
the latter ; and this is more important as we shall find in another
district the sandstones and breccias occurring under like circumstances.
The relations which exist between these several rocks show that the
outbursts of trap were anterior to the deposition of the sandstones and
breccias ; and this does not appear to be a mere local occurrence, but
tends to support the inference that the Coal-fields of the centre of
Scotland had not only been deposited, but had been subjected to all
those violent disturbances, and outbursts of igneous matter, which
are so prevalent among them, before the deposition of the sandstones
and breccias.
As in the other areas of sandstone which are found in Drumfries-
shire, we have no proofs that the causes which disturbed them have
affected the Silurians surrounding this area ; but the intermediate
Carboniferous strata partake to a great extent of the influences of
the forces which have disturbed the newer formation. From the
appearance of the breccias in the lower portion of these deposits, I
am disposed to consider them as the equivalents of the lower and