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J. W. JUDD ON THE SECONDARY BOCKS OF SCOTLAND. 247
numerable dykes. Associated with the agglomerates are numerous
ejected blocks

these comprise examples of nearly all the rocks
found beneath the lavas of Mull, including the Lower Silurian gneiss,
quartzite, mica-schist, and slate, the Newer Palaeozoic breccias, con-
glomerates, sandstones, and lavas, the Liassic rocks, and the Cre-
taceous quartzose conglomerates, grits, and sandstones.
At its northern end, as we approach the summit, the whole of
the highly siliceous rocks which compose the mass of the mountain,
granite, felsite, felstone lavas, and felspathic agglomerates, are seen
to be penetrated indiscriminately by numerous intrusive sheets or
dykes on the grandest scale, composed of various forms of gabbro,
passing into dolerite and basalt, which have evidently produced a
greater or less amount of alteration at the planes of contact in the
rocks which they traverse. These great intrusive sheets and d.dces
of basic igneous rock were, from their position, evidently at one time
connected with the great masses of gabbro forming Beinn Varnach
and the eastern portion of Beinn Tsalla, from which they are now
separated by the Forsa Glen. Owing to the manner in which these
gabbro dykes resist denuding influences their course among crumbling
rocks of the acid class can be easily traced by the geological observer.
The last point to be noticed with regard to Craig Craggen is that
the spur known as JN"id-a-shoag (the Hawk's nest) is capped by an
isolated patch of ordinary basalt, which, from its amygdaloidal
character is recognized as a portion of an old lava sheet

while,
overlapping the felstone lavas, towards the northern foot of the
mountain we find portions of the great series of basaltic lavas, which,
though cut off abruptly on the shores of the Sound of Mull, are seen
to be continued on the opposite side in Morvern. The relations of the
several masses of rock of the basic class are such as to leave no room
for doubt that the comparatively soft sCoriaceous masses of this moun-
tain owe their preservation to a covering of basaltic lavas, of which
the outlier of Nid-a-shoag constitutes the last vestige

and it seems
almost equally impossible to resist the inference that the lavas of
the great basaltic sheets were once actually continuous with the
great intrusive gabbro masses, which are composed of identical
materials with them though in a different state of aggregation.
d. Beinn More (Section, PI. XXIII. fig. 4). — To complete our series
of illustrations of the relations which the several volcanic products
of the island of Mull bear to one another, we cannot do better than
notice this, the highest peak in the island. In the lower parts of
this mountain and the spurs around it the granites, felsites, felstone
lavas, felspathic agglomerates, with the intersecting dykes of gabbro,
dolerite, and basalt may be observed presenting the relations to one
another which have been already described. Resting unconformably
upon these is a mass, many hundreds of feet in thickness and consti-
tuting the whole of the higher portions of the mountain, composed of
basaltic scoriae, tuffs, and ashes, alternating with lava sheets and in-
tersected by a plexus of dykes. By the thinning-out of the masse3
of agglomerate the basaltic lavas come together, forming the great
peninsula of the Bourg or Gribun, which is made up of lava sheets