THE ISLAND OF FOULA. 
^43 
is sometimes nearly compact, and so abundant, as, with- 
out its geological connections, would render the name of 
granite rather inapplicable At the point C, the ' un- 
stratified rock terminates, and a narrow cave or fissure 
at that place prevents an inspection of its contact with 
the succeeding rocks. On the south side of the fissure, at 
(C), gneiss rocks occur, dipping to 25° (S. of E.), at an 
angle of 45°, and extend for a space of a mile and a half 
to (cT), varying or curving in the direction of the strata, 
the most general being the magnetic north, nearly at right 
angles to the general dip of the sandstone. Subordinate to 
the gneiss occur beds of mica-slate, hornblende-slate, and 
compact felspar, and occasionally veins of large-granular 
granite present themselves. The junction, near the point 
d, of the sandstone and gneiss is effected by gradations so 
minute, as to render it difficult to point out the precise spotj 
affording a remarkable contrast with the junction of these 
rocks at the north end of the island. At the point a bed 
of unstratified quartzose rock occurs, apparently bending 
up the strata of the superimposed sandstone. Among the 
primary rocks of Foula, minute crystals of iron and copper 
pyrites often occur disseminated. 
The distinction of Primary and Secondary rocks in this 
island may be rather comparative than real ; for, though 
the sandstone occasionally partakes both of the character of 
primary sandstone and quartz-rock, it also alternates with, 
and at last passes into, sandstone of a much newer aspect. 
The Transition class, in this instance, seems a very conve- 
nient division to refer it to. 
* The nature and connections of this granite are somewhat similar to 
those of Ronas HiU and Ben Layel. 
Q 2 
