OLD RED SANDSTONE OF WESTERN EUROPE. 395 
stone and flagstone occurs at the base of the overlying strata, filling up hollows 
of the gneiss and allowing projecting parts of that rock to be wrapped round by 
the succeeding sandstones. This breccia is so hard and crystalline as to be in 
part scarcely distinguishable from a jointed granite. Some calcareous bands 
are here as usual associated with the base of the flagstones. A few small faults 
have the effect of here and there bringing the sandstones and the gneiss 
together along a vertical junction line. 
Westwards from this granitic interruption a noble range of mural precipices, 
culminating in the Cnoc Geodh Stoir (314 feet high), displays a characteristic 
section of beds in the upper flagstone group. As the dip continues to be 
N.N.W. to N.W., while the coast trends nearly east and west, a gradually 
ascending succession of strata is passed over until, at the mouth of Bighouse 
Bay, the dip bends round to N.N.E. Since, however, the angle of inclination 
remains the same (15°), and there is not room for the reappearance of more 
than merely the upper part of the series between this point and the crystalline 
rocks referred to, it is evident that the beds at Bighouse Bay must be several 
hundred feet higher in the flagstone group than those resting on the gneiss to 
the west of Sandside, and therefore higher than the typical calcareous and 
bituminous fish-bearing shales and flagstones of Sandside Head; the total 
depth of flagstones exposed between Holburn Head and Bighouse being per- 
haps not much under 1000 feet. Yet at the head of Bighouse Bay green 
and grey sandstones and sandy flags, with a band of striped limestone, occur 
as if again the underlying crystalline rocks existed immediately below. The 
strike of these strata carries them obliquely across the bay, and on the 
western side we actually again encounter the granitic platform, covered 
by breccias and sandstones. It is on the shore to the north of Portskerry 
that these strata and their relations to the old rocks, so well described 
by Sepe@wick and Murcuison* and by Hay CunnincHamt are best ex- 
amined. On the west side of the Portskerry harbour knobs of pink granite 
and gneiss are wrapped round and covered over by the sandstones, the uncon- 
formability being admirably displayed both on the low cliff and on ground plan 
upon the beach. The lowest strata, consisting of breccia, perhaps 20 to 30 feet 
thick but inconstant and sometimes absent, are red or pink in colour, owing 
mainly to the abundance of the included fragments of fine red granite. The 
angular detritus of this deposit has been obtained from the waste of the under- 
lying and surrounding crystalline rocks. The breccia passes up into pale-yellow 
and greenish sandstones, through which scattered pieces of granite or other 
crystalline rock may be observed, especially towards the base and where the 
breccia has thinned away. In one of these pale sandstones Mr Pracu found 
' * “Trans, Geol. Soc.,” 2d ser. vol. iii. See also Murcuison, “Quart, Journ. Geol. Soc.” vol. xv. p. 403. 
- + “Trans. Highland Society,” vol. vii. 
