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W. JUDD ON THE SECOXDARr ROCKS OF SCOTLAND. 263
The central and apical portion of the mountain of Beinn Shiant is
formed of rocks of similar petrological character, which, however, are
apparently of intrusive origin. On the northern side of the moun-
tain these rocks form a lofty and precipitous ridge.
The masses of columnar rock evidently constitute portions of a
number of lava streams which appear to have been originally in
connexion with the central mass, and to have diverged in a radial
manner from it. Some of these lava streams can be traced to very
considerable distances.
"Where the grassy slopes below the lava cappings of the spurs are
cut through by streams, they are seen to be composed of volcanic ag-
glomerates and breccias. These contain numerous angular frag-
ments of both the felspathic and basaltic lavas of earlier Tertiary
periods with some of the underlying Lower Silurian gneiss, such
being the rocks upon which the mass of Beinn Shiant is built up

mingled with these are numerous fragments of felspathic scoriae and
ashes, with many fractured and worn crystals of glassy felspar in-
cluded in the mass*.
Fortunately for the geologist, one of the spurs of Beinn Shiant is
cut across in a sea-cliff forming the headland of Srone More or
Maclean's Nose

and here we have a magnificent display of the
wonderfully interesting features in the rock-masses composing this
remarkable mountain. The upper part of Srone More, which rises
to a height of 1050 feet, is composed of the columnar lavas already
described

but the almost precipitous cliffs below are seen to be
made up of nearly angular blocks of all sizes, up to 6 or 8 feet in
diameter, heaped together in the wildest confusion, and presenting
no appearance whatever of stratification or of the sorting of the ma-
terials according to their specific gravity.
Lastly, it is necessary to notice that the great masses of agglome-
rate which constitute so large a portion of Beinn Shiant, together
with the older lavas and gneiss on which they are piled, are tra-
versed in every direction by dykes and veins of every size, composed
of similar rocks to those forming the lava streams — namely, trachyte
and " pitchstone-porphyry."
To any one familiar with the characters presented by Arthur's
of Beinn Shiant, and like them graduate, in consequence of the matrix in which
the felspar crystals are imbedded acquiring a glassy texture, into " pitchstone-
porphyry." In speaking of the Eocene acid lavas of the Hebrides, I have
preferred to apply to them the term "felstone," although it must be re-
membered that they present no essential points of distinction from recent
quartz-trachytes, either in chemical composition or mineralogical structure.
The later lavas of Beinn Shiant and the Sciir of Eigg present still fewer points
of difference from those of active volcanoes

and it would perhaps be more
correct to speak of them as "trachytes" than as " porphyrites."

The frequency with which crystals, often more or less worn and fractured,
of various volcanic minerals, such as augite, biotite, the felspars, &c, are thrown
out from the vents of volcanoes has been noticed by Mr. Scrope. Such crystals
are found alike in the recent ejections of Stromboli, and imbedded in the tuffs
connected with extinct volcanoes at Vulcano, Albano, Bracciano, Bocca Mon-
fina, and some of the puys of Auvergne.