354 T. O. Bosworth— Wind Erosion in Mull. 
the dune formation is accompanied by considerable rock erosion. On 
the north coast 33 miles north-west of Bunessan, and half a mile west 
of the bay called Camas Tuath, is a smaller bay marked on the 6-inch 
map as Traigh na Margaidh. It is one-sixth of a mile wide at the 
mouth and reaches thence one-fifth of a mile inland. In this inlet, 
which is bounded by granite cliffs, there is a wide stretch of white 
sand, which, followed inland, becomes a mantle of blown sand spreading 
over and banked up against the granite rocks. This sand is decidedly 
more worn than that on the beach, and the sorting of the grains is 
more complete. Magnetite grains are abundant in it; and from one 
sample 5 per cent. by weight was easily extracted with a magnet. 
The granite is coarsely crystalline and of homogeneous texture, 
without any parallelism of minerals or any sign of shearing. The 
joint planes here are vertical with directions 45° W. of N. and 
30° E. of N. 
The wearing of the rocks on the sides of the bay and on the 
hummocky masses more or less buried in the sand indicate within 
the inlet a prevalent N.N.W. wind, straight up the bay and up 
the ‘slack’ which is its landward continuation. The crests of the 
elongated mounds of sand which have formed on the lee side of the 
hummocks also have this trend, and the crests of the ripples are at 
right angles to it. 
The hummocks are elongated in the direction about 15° W. of N. 
They are often undercut and worn to a somewhat conical shape with 
the point more or less sharpened and facing the wind. (See 
Pl. XXVIII, Fig. 1.) On these windward ends smooth hollows 
have been formed in the felspar, and deep narrow-mouthed pits 
where mica has been, while the quartz stands out as tiny smooth 
knobs sometimes mounted on diminutive undercut stalks of pink 
felspar, like a minute collar stud. (See Pl. XXVIII, Fig. 2.) 
The surfaces of the rocks and hummocks are highly polished and 
curiously corrugated, being worn into regular ridges and furrows. 
(See Pl. XXIX, Fig. 3.) From the windward ends of the hummocks 
these radiate as from a focus, but on the flat surfaces they are more 
strictly parallel, trending N.N.W. The ridges vary considerably in 
dimensions; commonly they are about a quarter of an inch apart, and 
the furrows say one-tenth of an inch deep, but in some cases the 
ridges are an inch apart and the furrows one-third of an inch deep, 
and in others there are as many as ten ridges to the inch. Some- 
times there are major and minor corrugations. The furrows are 
formed in felspar, but each ridge begins abruptly at its windward 
end with a quartz crystal worn into a smooth polished convex cap 
and often almost worn away. ‘The remainder of the ridge consists 
mainly of pink felspar sheltered from destruction by the quartz, and, 
unless some more quartz is encountered, the ridge dies out in the 
course of an inch or two. Both quartz and felspar are so highly 
polished that they have a sub-pearly lustre. 
Loose boulders of granite, that probably have not lain long in place, 
are corrugated like the rocks, and a loose block of basaltic rock from 
a neighbouring dyke was seen to be fluted in a somewhat similar 
way, a relatively large crystal of ferromagnesian mineral forming the 
