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TRANSACTIONS

OF THE

‘GEOLOGICAL SOCIETY,

ESTABLISHED NOVEMBER 13, 1807.

VOLUME THE THIRD.

Quod si cui mortalium cordi et cure sit, non tantum inventis herere, atque iis uti,
sed ad ulteriora penetrare ; atque non disputando adversarium, sed opere naturam
vincere ; denique non belle et probabiliter opinari, sed certo et ostensive scire ; tales,

tanquam veri scientiarum filii, nobis (si videbitur) se adjungant.
Novum Organum, Prefatio.

LONDON :

PRINTED AND SOLD BY WILLIAM PHILLIPS, GEORGE YARD, LOMBARD STREET.

1816.

i aE UR A

AATF ABKAWOS AHRT 5 n MALISIW $4 GNOR Gan Garuiaa

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OFFICERS AND COUNCIL OF THE GEOLOGICAL SOCIETY,
ELECTED FEBRUARY 2, 1816.

PRESIDENT,
JOHN MAC CULLOCH, M.D. F.L.S.,

VICE-PRESIDENTS,

The Right Hon. Earl COMPTON, M.P. HENRY WARBURTON, Esq. F.R.S.
The Hon. HENRY GREY BENNET, M.P.F.R.S.| WILLIAM HYDE WOLLASTON, M.D.
Sec. R.S.
SECRETARIES,
ARTHUR AIKIN, Esq. | CHARLES STOKES, Esq. F.A. & L.S.

FOREIGN SECRETARY,
AUGUSTUS’ BOZZI GRANVILLE, M.D. F.L.S.

TRE ASURERS,
DANIEL MOORE, Esq. F.R. & A.S. | JOHN TAYLOR, Esq.
COUNCIL,
WILLIAM BLAKE, Esq. F.R.S. HENRY HOLLAND, M.D. F.R.S.

THOMAS COLBY, Esq. Captain of the Royal The Marquis of LANSDOWNE, F.R.S.
Engineers. .
ALEXANDER MARCET, M.D. F.R.S.
Sir HENRY CHARLES ENGLEFIELD, Bart.
F.R.A. L.R.S. Ed. & A.S. Newc. M.R. Inst. The Right Hon. Sir JOHN NICHOLL, M.P.
F.R.S.

GEORGE BELLAS GREENOUGH, Esq.
E.R. & L.S. WILLIAM HASLEDINE PEPYS, Esq. F.R.S.

THOMAS HARRISON, Esq. F.R.S. Sec. Roy. SAMUEL SOLLY, Esq. F.RS.

& Afr. Inst.
JOHN WHISHAW, Esq. F.R.S.

KEEPER OF THE MUSEUM AND DRAUGHTSMAN,
Mr, THOMAS WEBSTER.

TRUSTEES OF THE GEOLOGICAL SOCIETY.

GEORGE BELLAS GREENOUGH, Esq.
Sir ARAHAM HUME, Bart. M.P,

FRANCIS HORNER, Est. M.P.
WILLIAM BABINGTON, M.D.
ROBERT FERGUSON, Esq.
DAVID RICARDO, Esq.
SAMUEL WOODS, Esq.

ADVERTISEMENT.

Tue Editors of the Transactions of the Geological Society
are directed to make tt known to the Public, that the Authors alone are

responsible for the facts and opinions contained in their respective

papers.

Geological Society, :
August 1, 1816.

Tt ts requested that all letters and communications to the
Secretaries, and presents ta the Society, be addressed to the House of

the Geological Socicty, No. 20, Bedford Street, Covent Garden, London.

ERRATA.

Page 11, line 19, for where read were

32, 20, chist schist

49, —— 16, —— interferes intervenes .
56, —— 10, —— Eishort — Loch Eishort
74,—— 1, —— external — eternal

90, —— 17, —— ichthyopthalmite —— ichthyophthalmite
137, —— 23, after 2257 insert feet

141, ——— 21, for Cushendun read Cushendon
164, —— 20, —— applied supplied
197, —— 5from the bottom dele being flat
238, —— 13, for mytuli read mytili

311, === note. Plate 1 Plate 13

CONTENTS,

I. A Sketch of the Mineralogy of Sky. By John MacCulloch, M.D. F_L.S.
President of the Geological Society, Chemist to the Ordnance, and
Lecturer on Chemistry at the Royal Military Academy at Woolwich p. 1

II. On the Oxyd of Uranium, the production of Cornwall. By Mr. Wm.
Phillips, Member of the Geological Society - = pele

III. On the Geological Features of the North-eastern Counties of Ireland.
Extracted from the Notes of J. F. Berger, M.D. Member of the
Geological Society. With an Introduction and Remarks, by the
Rev. W. Conybeare, Member of the Geological Society wp. feu

Descriptive Notes referring to the Outline of Sections presented by a
part of the Coasts of Antrim and Derry. By the Rey. W. Conybeare,
Member of the Geological Society - - - ~ p. 196

IV. On the Dykes of the North of Ireland. By J. ¥. Berger, M.D.
Member of the Geological Society - - =~ p. 223

V. Some Remarks upon the Structure of Barbadoes, as connected with
Specimens of its Rocks. By get ares M.D. Physician to the
Forces - - - =". p. 20

VI. Outlines of the Geology of Cambridgeshire. By the Rev. J. Hailstone,
F.R. & L.8. Woodwardian Professor in the University of Cam-
bridge - - - - - p. 243

VII. Some Observations on a Bed of Trap occurring in the Colliery of
Birch Hill, near Walsall, in Staffordshire. By Arthur Aikin, Esq.
Secretary to the Geological Society. - - - ip. 25

CONTENTS.

VIII.A Geological Description of Glen Tilt. By John Mac Culloch,
M.D. F.L.S. President of the Geological Society, Chemist to the
Ordnance, and Lecturer on Chemistry at the Royal Military Aca-

demy at Woolwich - - - - - — p. 259
IX. Sketch of the Geology of the South-western Part of Somersetshire.

By Leonard Horner, Esq. F.R.S. Member of the Geological Society p. 338
X. Description of a Clinometer. By Lord Webb Seymour, F.2.S.

F.R.S. E. F.L.S. Member of the Geological Society =. Pp. oOo
XI. A Sketch of the Geology of the Lincolnshire Wolds. By Mr. Edward

Bogg, Land Surveyor - - - - p. 392
XII. On the Tremolite of Cornwall. By the Rev. W. Gregor, FTonorary

Member of the Geological Society - - - p. 399
XIII. Some Observations on the Salt Mines of Cardona, made during a

Tour in Spain in the Summer of 1814. By 'Thomas Stewart Traill,

M.D. Member of the Geological Society. - - p.404
XIV. Description of a new Ore of Tellurium. By Professor Esmark,

of Christiania. Foreign Member of the Geological Society - p,418
XV. An Account of the Swedish Corundum, from Gellivara in Lapland.

By C. T. Swedenstierna - : 2 - pAls
List of Donations - - . - - p. 421
Index = - - - + ~ p. 453

. TRANSACTIONS

OF THE

GEOLOGICAL SOCIETY,

I, Sketch of the Mineralogy of Shy,

_ By Jonn MacCunzocs, M.D.F.L.S. President of the Geological Society,
Chemist to the Ordnance, and Lecturer on Chemistry at the Royal
Military Academy at Woolwich.

Read January 6, 1815.

A FEW weeks residence in the island of Sky having enabled me to
give a general idea of its geological structure, I shall make no apology
for offering this paper, however incomplete, to the Society. Want
of further opportunities may perhaps for ever prevent me from
rendering it more perfect, as it may equally prevent others from
visiting that island. Nor is a district of such magnitude and inter-
est, of which the distance is so great, and the inconveniences of
climate and ground so considerable, likely soon, to offer to others
greater facilities than those, which enabled me to draw up. this
sketch. Should it prove otherwise, my object will at least, in its
VOL. ir, A

2 Dr. Mac Curxrocn’s Sketch of the

principal view, be fulfilled, since I shall have opened a path for
others to follow, and traced an outline which some more fortunate
observer will with greater ease complete.

The variety of rocks which occurs in this island, as well as the
theoretical difficulties in which the connection and order of many
of these are still involved, and which are in some measure at least
elucidated by their appearances here, render this island very inter-
esting to the geologist. In attempting to describe them so as to
give a clear topographic view of their situations, and at the same
time to trace their connections with each other, (that object which
is more peculiarly an essential part of geological science,) I have
experienced difficulties which other observers must also have felt,
and from which I have but imperfectly succeeded in extricating
myself. It is to be hoped that our increasing knowledge will at
some future day diminish, if not remove, these difficulties, and _
smooth the path for the future historians of the earth’s surface and
structure. In the mean time no greater impediment to the progress
of that knowledge of which we are in search can be contrived,
than that of assuming a certain regulated order, founded on im-
perfect and limited, or on prejudiced observations. This proceed-
ing not only renders all investigation nugatory in itself, but accu-
mulates by the establishment and diffusion of false canons, a con-
stantly increasing load of obstruction to the progress of truth. The.
phenomena which have occurred to me in Scotland, during many
years examination of that very instructive country, have so often
led to conclusions different from those which have been supposed
already established, as to compel my dissent from that system of
general rules on which we have hitherto been taught to rely, At
the same time, convinced that generalization on this subject was
premature, and warned as much by my own discrepancies as by the

Mineralogy of Sky. 3

errors of those who have preceded me, I have rarely if ever at-
tempted to draw such general conclusions. My chief endeavour
has been to reduce questions of this nature to a narrow compass,
where the limits admitted of contraction; and where any thing has
appeared uncertain or contradictory, to put those uncertainties and
contradictions in the clearest light, that future observers might di-
rect their attention to those points-which most stand in need of
elucidation.

To place the subjects which have occurred in the examination of
Sky, in an order as nearly as possible both conducive to topogra+
phical clearness and geological elucidation, I have varied the order
of description as circumstances dictated. When the structure was
simple, and the geographical details corresponded, the task has been
easy to the writer, and will be easy to the reader. When it has
been otherwise, I have attempted as far as possible to reconcile .
these claims; while in the greater number of instances, where the
intricacy of the geological structure and the scattered disposition of
the materials over a large extent of surface have prevented all pos-
sibility of reconciliation, I have been obliged in some measure to
divide the subject with a reference to both these objects, preferring
to incur the charge of prolixity rather than that of obscurity. I
shall therefore commence by giving a general sketch of the se-
veral rocks which form the island, noting their geographical posi-
tions as accurately as circumstances permit; after which I shall
attempt to trace their geological arrangement, entering more largely
on those details which lead either to useful doubts or probable elu-
cidation.

The want of accurate geodesic operations has left the form, di-
mensions, and position of Sky, as yet desiderata in British geo-
graphy, an inconvenience however, much less in a geological view

Az

4 Dr. Mac Cutrocn’s Sketch of the

than that which arises from the want of an accurate detailed map of
its surface, its mountains, rivers, bays, and lakes ; data, without which
it is extremely difficult to give such particulars as could be desired
of the situations, boundaries, and connections of its several rocks;
a difficulty too not a little increased by the utter impossibility of ob-
taining the vernacular names from the natives, who are neither well
informed on the subject nor very well agreed in their application.
The want of ascertained distances and of fixed points of reference,
arising from the vacant state of many tracts and the loose manner
in which the Highlanders compute their miles, add not a little to
the trouble of giving precise descriptions. |

If we may trust to the latitudes and longitudes laid down, and
they are the only documents on which we have to rely, the extreme
length of this island is about forty-five miles, and its extreme
breadth about twenty. Its form is that of an irregular parallelogram,
so much intersected by deep sea lochs that scarcely any point on its
surface is five miles distant from the sea. It is divided into geogra-
phical districts, which, as they bear some relation to the physical
divisions of its surface, and will be necessary points of reference in
describing its structure, I shall here enumerate.

Of these, the southernmost is the district and parish of Sleat, a
tract of moderate and irregular elevation, terminating in the high
group of mountains which approaches the main land, and which, in
‘conjunction with Glen Elg, forms the narrow passage of the inner
sound. This is bounded to the north by the parish of Strath, an
open irregular valley, intersecting the island from N.E. to S.W.sand
separating the before-mentioned district from the remainder of the
island,” more particularly from the group of mountains which occu-
pies its middle division. A tract of uneven land extends from
Broadford along the eastern shore to the eastern Loch Eynort, and

Mineralogy of Sky. 5

over a high ridge to Sconser, where it ends:at in Loch Sligachan,
being bounded on its western side by the terminations of the before-
mentioned group of mountains. The high hill forming the island
of Scalpa is but barely separated by a narrow arm of the sea from
this tract. An imaginary boundary drawn from Strath to the head
of Loch Slapin on one side, and from Sconser to the western Loch
Eynort on the other, includes part of the district of Minginish, and
is still more remarkable as a physical division, since it contains the
lofty and formidable group of the Cuchullin hills, with other
mountains, of which the greater number are either nameless, or.
only recorded in the traditional geography of shepherds. This is
the only part of Sky which can properly be called mountainous,
and of which the aspect and character are perfectly distinct from:
those of the remainder of the island. The small district of Strath-
aird, more remarkable for its physical structure than its extent, is

interposed to the south of this tract, lying between Loch Slapin
and Loch Scavig. The northern and larger division of the island
which exhibits a great uniformity of physical character considerably
distinct from those now enumerated, contains the extensive districts
of Trotternish, Vaternish and Bracadale, the former occupying the
eastern and the two latter the western side of the island.

. The whole of this tract is hilly and uneven, yet cannot be consi-
dered as mountainous, except perhaps on its eastern side, where one
irregularly elevated and continuous ridge extends from Portree to
Ruhunish. Some high ground also occurs about Dunvegan, but the
rest is an undulating tract of hill and moor country.

The indentations which form the sea lochs are in some cases deter=
mined as on the continental land, by the vallies which are interposed
between ridges of hills, and in this case they are also the aestua~
ries of the rivers. But many of them are merely sinuosities of the

6 Dr. Mac Cuttocn’s Sketch of the

general boundary, receiving no streams of magnitude. To the
former belong the narrow lochs Slapin, Scavig, Brittle, Harpart,
Eynort, Eishort, Sligachan, and Portree; lochs Bracadale, Follart,
and Snizort, belong to the latter.

Although the elevation of the country is considerable, and the
climate among the most rainy of this kingdom, Sky affords no
rivers of magnitude: their course is too short to admit of the accu-
mulation of large streams. ‘The river which runs into loch Sli-
gachan carries more water to the sea than any other, and
after it perhaps follow in order those which run into the lochs
Harpart, Slapin, Eishort, Bracadale, Portree, Snizort, and Broad-
ford. The other streams are rivulets scarcely worthy of enume-
ration. ‘The drainage of the whole country is determined by the
positions of the hills and sea lochs, and may readily be collected
from the preceding observations. ‘There are three or four fresh-
water lakes, but of small size, and, except those of Coruisk and
Colmkill, hardly worthy of thename. The courses of these streams
exhibit but small traces of the wasting of the land. Like other
mountain torrents they bring down at times rubbish and stones, but
these bear no proportion to those accumulations of loose matter so
common on the main land, nor do they offer any example of
transported materials of which the origin is not to be traced to some
neighbouring rock.

The surface of Sky appears at first sight one continued tract of
brown moor, a dreary region of heath, and rock, and bog. Rugged
mountains exhibiting naked spires of bare rock of which the sides are
covered with ruins, lofty cliffs whose bases are whitened by a
boisterous sea, a stormy atmosphere with almost incessant rains,
complete the wild picture which first meets the eye of a stranger.
Yet a more intimate acquaintance discovers scenes of grandeur and

Mineralogy of Sky. 7

sublimity exceeded by no part of Scotland, abounding as it does in
the picturesque and romantic, and a more accurate survey of the
island shows spots with a fertility and population surpassed by few of
the highland districts ; together with a climate nearly as mild, and
a temperature as equable as that of the western parts of England.

The district of Sleat, conststing of decomposed schistus, possesses
along its. eastern shore a highly fertile tract with an excellent and
deep soil, adapted to the growth of all kinds of grain, and display-
ing pastures of perennial verdure. Similarly fertile soils are found
in the vallies on its western side, while the central division, formed
of syenite or quartz rock, produces the usual covering of those rocks,
heath. In Strathaird, nearly the whole peninsula of which con-
sists of secondary strata, we find a soil as fertile as we should ex-
pect on such a basis and in such a climate; a soil however owing
less to art than to nature, whose bountiful efforts are seldom much
assisted by highland industry or knowledge. A great part of the
district of Strath lies on a bed of limestone, and appears from its
natural grasses and its general aspect to possess all the requisites for
culture, or at least for an improved system of pasturage. But it
has hitherto been much neglected, and remains an almost useless
tract of wasted and scanty herbage encumbered with rocks and
stones, undrained, unfenced, and untilled.

Nature may be said to have denied a soil to the mountain tract —
which I have before described as forming the centre of the island,
and these hills adapted for no other system are imperfectly occupied
by sheep, of which from their rocky and sterile nature they can
maintain however but a scanty proportion. A few stags yet remain-
ing in these almost inaccessible regions divide with them this barren
range. The lower pastures are more advantageously occupied by the

8 Dr. Mac Cuttrocn’s Sketch of the

well known and celebrated breed of black cattle which forms the
staple produce of Sky.

The stony district about the Kyle ric’h produces like the Cuchullin
hills but a scanty covering of heath and grass, and is perhaps among
the most unproductive of the island, since the decomposed quartz
rock of which it consists, yields a soil even worse than the syenite
of the Red hills, or the rocks of the Cuchullin group; yet on the
sea shores a few fertile spots are found in cultivation.

The great northern division consists of one entire mass of trap,
with the exception of a few narrow lines of limestone and sand-
stone to be found on some of the shores. In various parts of this
tract there are to be seen districts of considerable fertility, admitting,
under the highland system of cultivation, a perpetual rotation of
corn, with no alternation of green crops or fallow except the occa-
sional one of potatoes ; the hay as is usual under the same system
of farming being collected from wet meadows and waste patches of
land. ‘The most considerable of these corn districts is in Trotter-
nish, which for many miles displays an extent of cultivation ex-
ceeded by few highland tracts, and is emphatically called the granary
of Sky. The aspect of loch Uig under the new crofting system is
in this respect highly interesting. In various parts of the sea shore
about loch Snizort and loch Follart, as well as in the vicinity of
loch Bracadale, similar fertile: tracts occur, and the little retired
valley of Talisker might in a drier climate compare in fertility with
the most chosen spots of our own southern counties.

Since chemistry has lately, although perhaps hitherto with little
success, lent its speculative aids to the improvement of agriculture,
it will not be foreign to the views of the geologist to examine how
far his science also may bear upon this first and fundamental of all

Mineralogy of Sky. 9

arts. From the identity of rocks in different tracts a conclusion
may be drawn with regard to the identity of the resulting soils, and
the analogies discovered in them may perhaps with less trouble and
as great certainty as any chemical analyses, lead agriculturists to
hazard those experiments in improvement which seem justifiable
from similarity of composition no less than similarity of climate and
exposure. I shall therefore I trust be excused for dwelling a little
longer on a subject intimately connected with geological science, and
in itself among the most practically interesting that can occupy our
attention. .

It is already well known that many of the rocks of the trap
family, like some lavas, afford on decompositicn one of the most
fertile soils with which we are acquainted. On former occasions
I have mentioned this fact, and noticed at the same time the great
differences which appeared in this respect in different situations
where there was nevertheless a considerable resemblance in the
rocky substratum. ‘The different proportions of calcareous earth, of
alkali, and of carbon, which latter appears to be an ingredient in.
some traps, are probably the circumstances which constitute the chief
differences in this case; but with this we must also consider that the
various rocks of this class differ in composition ‘in perhaps a greater.
degree than any others with ‘which we are acquainted, and that
together with this essential variation in their composition, they also
possess infinite varieties in hardness, and in the property of decom~
posing by the action of air and water. Many considerations must
therefore enter into our views before we can decide on the fertility
of the resulting soil, unless it be actually exhibited in those places
where decomposition has already taken place.

In the district of Sky which I am now considering, there appears,
as far as an accurate mineralogical investigation can determine such

VOL. III. )

10 Dr. Mac Cutrocn’s Sketch of the

a point without the aid of analysis, a considerable similarity of com-
position in the trap throughout the greatest part of the whole tract.
In almost every place where the rock approaches the surface, it is found
on cutting into it to be rotten to a considerable depth, often reduced
superficially to an absolute soil, and although appearing below
like a solid rock, capable of being cut without difficulty by the pick-
axe or spade. Occasionally it decomposes into a soil perhaps more
gravelly in some situations than in others, but in this case there
appear only time and a further continuance of the destroying
powers requisite for its complete change. Where the decomposition
is most perfect it forms a clayey loam of which the aspect at least is
favourable, and of which the fertility also is probably not so limited
as the appearance of the heath and grasses which it bears would at
first sight induce us to believe. The trap which I have mentioned
is remarkable for the enormous quantity of zeolites imbedded in it,
the mineralogical details of which I shall have occasion to speak
more largely of hereafter. In the decomposed soils these are frequently
found resisting change long after the rock is rotten and reduced to
clay. But in many other cases they also are decomposed together
with the soil, and in such quantity as to communicate their white
colour to it, and with that colour doubtless a degree of additional
fertility derived from the quantity of calcareous earth which they
contain. In many places such accumulated beds of decomposed
zeolites occur that they have been mistaken for marl, and have :
when used produced similar effects ; although the narrow and sloven-
ly system of cultivation practised by these little highland farmers
neither admits of a full trial nor of a fair result.

We have seen that many tracts of this district are characterized
by a high degree of actual fertility, while neighbouring ones formed
of a soil apparently identical and under similar circumstances of cli-~

.

Mineralogy of Sky. 11

mate and exposure, are still covered with unprofitable. heath and
peat, producing a scanty and almost useless herbage. It'is worth
our while to inquire into the causes of this difference, and to see if
valid ones cannot be assigned. .

In the land already under tillage it is obvious that the subsoil: is
covered with a soil actually in use, consisting of vegetable mould
annually loosened by the spade or plough, and admitting the pene-
tration of light, of air, and of water, to the subjacent and half de-
composed matter. In the uncultivated neighbouring tracts we shall
on the contrary find it covered with a thick mass of peat, the imme-
diate soil on which the heath, the sphagnum, the carices, and the
rushes alternately flourish and die, adding fresh matter to this already
impenetrable substance, Neither air, light, nor water can make their
way through this dense covering of a substance so notoriously im-
pervious that it has been found of equal use with clay in puddling
the artificial banks of canals. .It forms in fact an adventitious and
useless soil so entire and so impenetrable that it would be of
equally little consequence to the land-owner in its. present state,
whether it where bedded on a rock of solid quartz or on the most
fertile garden mould. Fortunately this covering of peat is rarely so
deep that the plough or the caschrom. (the crooked spade. of the
Highlanders) cannot reach to the bottom of it. The remedy and
obvious method of improvement is pointed out by the relative con-
dition of the fertile and the barren parts of this tract. The few ex;
periments which have been tried have proved eminently successful,
and among them I may point out those performed by Mr. Mac-
pherson at Portree, By the admission of air and water the progress
of decomposition is accelerated, and the rock is reduced in no long
space to a useful soil. ‘The texture of the peat is at the same time
Idosened by its admixture with the decomposed rock, and being thus

B 2

12 Dr. Mac Cuttocn’s Sketch of the

preserved in an open state and subjected to the changes which pul-
verization and access of air always produce on it, adds the carbona-
ceous ingredient to the clay, and forms a true vegetable mould. It
is a separate question depending on various other considerations,
whether this species of improvement should in all cases be directed
to the cultivation of grain; but there is no doubt that it could be
easily turned to a system of ameliorated pasturage, a system under.
which, without exaggeration, one acre of land could be made to
produce more than many hundreds in its present state.

It is not my business to inquire into the obstacles which impede
this obvious improvement of a country possessing such capability.
Want of capital may be one cause, but it is more probable that the
chief impediments are of a moral nature, resulting partly from the
characteristic indolence and contentedness of the inhabitants, and
partly from the difficulties which always attend the introduction of
novelty into practices long established.

The want of trees in this island must be attributed to similar
causes, since they would grow well in innumerable sheltered situa-
tions, and since some parts of the island still exhibit the remains of
ancient woods.

In mentioning the artificial divisions of Sky, I have already
touched slightly on its general irregularities and the disposition of
its surface, but as these are intimately connected with the arrange-
ment of its rocks, they require a more detailed consideration.

The principal group of mountains is that of the Culin or Cuchul-
lin, so named from the well known traditional hero and king of this
island. ‘This forms an irregular mountain tract covering an area
of ten or twelve miles by seven, and skirting the sea shore with a
very bold series of declivities from near Loch Eynort to Loch Scavig.
The single mountain Blaven forming a long ridge between the lochs

Mineralogy of Sky. 13

of Scavig and Slapin, may be classed with this group of the Cuchullin,
as it resembles it in altitude and aspect as well as in mineral com-
position, and thus adds about ten more square miles to the space
occupied by the particular class of rocks of which this group is
composed. The whole of this compound group is strongly distin-
guished from the associated and neighbouring mountains, as well as
from all the other mountains of Scotland, by the spiry and rugged
forms of its outline, which presents a series of naked rocks and
towering cliffs destitute of vegetation, and rising dark through the
mists which seem for ever to hang on its stormy summit. The
mountains of Arran, alpine and serrated as they are, bear no com-
parison with them, and the far famed scenery of Glenco almost
sinks into insigniftcance before the terrific grandeur of the Cuchullin
hills.

It is to be regretted that no observations have yet been made to
determine the altitude of this group; a want which I was unfortu-
nately in no condition to supply: but from that sort of experience
in the elevations of hills which is acquired by long habitude in a
mountainous country, and by comparing them with ascertained eleva-
tions from different points of view, a rough estimate may be formed
of its altitude, which must at least suffice till some more fortunate
traveller shall place his barometer on the summit. They do not
fall short of three thousand feet, and in all probability exceed it.
A general idea of their ground plan may be conveyed by saying
that they form an irregular and curved ridge of a very intricate shape,
giving rise to numerous streams, the waters of which, for the most
part, are discharged into the western sea; this proceeds from the
inclination of the hills, the principal escarpements of which, how-
ever irregular, look towards the east and north.

This group is intimately connected with another, which for the

14 Dr. Mac Cutiocn’s Sketch of the

sake of perspicuity I shall distinguish by the name of the Red hills,
a name very characteristic of their colour as contrasted with the livid
black of the Cuchullin, and excusable in as much as it is applied by
the natives to some of the principal hills of the group. I would
gladly have given the name of each individual, but I was unable to
procure them, no general surveys having been made, and the parti-
cular surveys of estates, either neglecting to notice them, or, like the
shepherds, differing so much in opinion as to lead to inextricable
confusion. Fortunately it is not material, as their uniformity of
structure is so great, that the description of one is nearly applicable
to the whole of the group. The general outline of these hills forms
a character as highly contrasted to that of the Cuchullin as are their
respective colours. In place of the lofty spires, the impending pre-
cipices and the almost unalterable rocks of those, we see in the Red
hills a continued succession of tame rounded outlines, the effect of a
decomposition which has covered them with ruins and almost
every where concealed from view the natural rock. They also fall
far short of the Cuchullin in elevation. ‘Those which are entirely
red, and which, as will be hereafter seen, consist of a syenitic rock, do
not approach, within many hundred feet, the height of the former,
and the loftiest of the group, among which that of Glamich takes
precedence, will be found to consist of a mixture of the syenitic rock,
and that clinkstone, which, as I shall hereafter show, constitutes a
portion of the mass of the Cuchullin.

Comparing from the summits of any of the hills the general aspect
of the two groups, the spectator is inevitably struck with the different
powers of resistance which the two classes of rock offer to the efforts
of time, and looks forward perhaps to a distant day when the red
hills shall be levelled with the land below, while the Cuchullin shall
still lift its iron summit to the clouds. There is yet another charac-

Mineralogy of Sky. © - 15

teristic difference between the two groups. We have seen that the
Cuchullin and Blaven form one irregular mass, continuous in the
ridges and much confounded both with each other and the general
mass of the island. But the Red hills form rather a distinct assem-
blage of mountains, being separated either singly or in small associa-
tions by deep vallies, and placed as it were upon the general level.
This group is bounded on the west by the vale of Strath, which ex-
tends from Broadford to the head of Loch Slapin, and skirting the
sound of Scalpa terminates at. Loch Sligachan. _ I may add that ex-
cept the slight mixture of substances which appears to take place in
Glamich hill, and in one or two more of those which come into con-
tact with the Cuchullin and with Blaven, these two groups do not
interfere, but are composed respectively of. different and well cha-
racterized rocks.

The great mountain of Blaven is skirted by lower hills, descend-
ing gradually into the table land of Strathaird, which we shall
hereafter see to be the largest portion of the secondary stratified
rocks existing in Sky. ,

An uneven land, rising into irregular low hills, occupies the whole
tract to the southward of the valley of Strath, with the exception
of a nook which may be defined by an imaginary curved line
drawn from Loch Oransa to the castle of Inverfuchag. This part
of the island forms another distinct mountain group rising into
two principal summits, and attaining an elevation apparently of
fifteen or eighteen hundred feet. :

The general elevations of the remainder of the island may be
discussed in a few words.

Having passed Loch Sligachan, an irregular ridge of high land
appears branching in two directions: The main ridge occupies the
eastern side of the island to Portree, where it is interrupted by the

16 Dr. Mac Curitrocn’s Sketch of the

harbour of that place. Resuming thence its northern direction it
continues to rise gradually for twelve or fifteen miles, and declines
as gradually to the northern extremity of the island at Ruhunish.
This ridge shows a gentle declivity to the west while to the east
it frequently presents a rocky and broken escarpement. As far as
its elevation can be estimated by the aspect of the view from its
summit, and by comparing it with other known elevations when
seen from the sea, it seems to reach at least the height of fifteen
hundred feet. It may even be more considerable, since the gra-
dual ascent of the land around it tends to make it appear lower
than it really is.

As the abrupt face of this ridge is directed eastward, it thus
forms a second and interior range of cliffs which in many places
rises to a considerable height. ‘The most remarkable of these is
to be seen at the Storr, from whence it extends for some space
northwards. The precipices which form the eastern face of the
Storr offer scenes to the lover of the picturesque not exceeded
either in singularity or grandeur by any thing which is to be seen
in Scotland, and almost as little known to the natives as to casual
travellers. In the progress of decomposition vast fragments have
been detached from the body of the hill, and continue insulated on
its slope, resembling at a little distance the remains of ancient castles
and the spires of ruined cathedrals. One remarkable conical rock
attains a height of about an hundred and fifty feet, its base not ex-
ceeding twenty in diameter, forming a sea mark as conspicuous to
the vessels which frequent this coast, as it is striking in a pictu-
resque view.

The mineralogist, no less than the admirer of fine nature, will be
gratified by the examination of the Storr. It consists of an amyg-
daloidal rock, containing abundant specimens of the zeolite family,

v

SOS

5

.

Mineralogy of Sky. {7

which I shall have occasion to describe in their proper place.
The other ridge which I mentioned as branching from it, is con-
siderably lower, and consists in fact of uneven undulating ground,
stretching away to the north-west till it reaches Vaternish point.
The western peninsular division, from Dunvegan head to Macleod’s
Maidens, is a tract of high land containing the two remarkable flat
topped mountains known by the name of Macleod’s Tables, the height
of which appears to be similar to that of the great eastern ridge.
What remains of the island is one irregular table land, offering hills
which in any. other situation would appear considerable, but which
lose their importance in the vicinity of the towering Cuchullin.

I have reason to think that in the general estimate here given of
the elevations in Sky I have fallen short instead of exceeding, and
shall be glad if future observers shall determine these altitudes with
correctness. I scarcely however consider it in any other light than
as a question of geography, as the increased examination of geo-
logical phenomena has proved that there is no general or necessary
connection between formations of particular rocks and given ele-
vations. Equally unfounded appear those rules which have, as.
recent observations show, been prematurely laid down respecting
the outgoings as they have been called of the several classes of rock.
The irregularities of these outgoimgs, not only absolutely but re-
latively, seem to point out to geologists a department requiring at
least a very careful review, if not an absolute elision from the laws
of the science.

I have nothing to add to the description of the rivers which I
gave in speaking of the geographic divisions of the island, and
the remarks I have to make on the waste of the land will be com-
prised in a short space.

VOL, III. C

18 Dr. MAc Cutrocn’s Sketch of the

I have already said that I did not observe in any part of Sky
those accumulations of foreign and transported materials which are
of such frequent occurrence on the main land of Scotland, and of
which I have already noticed a remarkable example in Staffa. The
accumulations of matter which it offers in several places are but
trifling, and they are evidently derived from the daily action of
the rivers, or from the ruin of the exposed rocks. |

Commencing at Loch Slapin a considerable alluvium may be ob-
served occupying the head of this Loch and extending up Strath-
more, encroaching on the top of the bay, and evidently formed by
the waste of the Red hills, with additions comparatively insig-
nificant from the naked precipices of Blaven.

As the upper end of Loch Eishort receives no river of note, it
presents no alluvial deposit, and no further marks of waste, en-
croachment, or alteration of the sea line, are to be observed round
the point of Sleat till we reach Loch Oransa. Partial depositions
of gravel may be traced from hence round the shore to Kyleaken,
where a considerable bank of alluvial matter has been thrown up,
apparently from the concurring action of the rapid tides which run
through the sound of Sky. Opposite the island of Scalpa a sort of
delta has been formed, which bids fair at some future day to unite
the two islands into one. The head of the eastern Loch Eynort is
also the receptacle of considerable masses of rubbish brought down
from the Red hills, a waste sufficiently great to alter the courses of
the small streams which run through the narrow vallies separating
these hills. Similar, but more extensive, accumulations from the
same cause have formed a tract of plain ground at the head of
Loch Sligachan, subject to frequent inroads and changes from the
still varying course of the stream. The waste of the land which,

Mineralogy of Sky. 19

supplies the river running into Portree harbour appears to have had
some effect in filling up its southern branch which the ebb of the
loch has no tendency to remove. From below Portree to the nor-
thern point of the island, the coast consists of high cliffs of trap,
which exhibit the species of decomposition characteristic of these
rocks, in the vast slopes which decline from them'to the shore
wherever the action of the tide has not been sufficient to prevent
that accumulation. Continuing round the point of Ruhunish,
similar cliffs of trap resting on the secondary strata extend to the
bottom of Loch Snizort, at the end of which as well as of Loch Vig
the same appearances of encroachment are visible. The parish of
Kilmuir offers the only considerable tract of alluvial land in Sky,
from which its superior and long established fertility is probably to
be accounted for. I cannot speak positively of the shores which
form the point of Vaternish, having only seen them from a dis-
tance, but as they resemble both in aspect and composition the di-
vision of Trotternish just noticed, it is probable they possess no
great peculiarity in this respect. Neither does Dunvegan offer any
thing worthy of remark.

The shores of Loch Bracadale exhibit when low, considerable
portions of clayey alluvial soil, characterised like those of Kilmuir
by extraordinary fertility. A similar alluvium may be observed at
the head of Loch Harpart, and the little valley of Talisker appears
to have been entirely gained from the sea at some distant period,
by a combination of the waste of the land with the counteracting
efforts of the western swell, which has thus formed a natural em-
bankment for its further protection.

A remarkable difference is to be seen along the whole western
shore of the island from Dunvegan head to Loch Brittle, between

cZ

20 Dr. Mac Cutiocn’s Sketch of the

the effects of the eastern and the western sea. I already observed
that the eastern cliffs were covered by a slope of alluvial ground
descending to the sea; but the western, though formed of the
same rocks, offer an almost continued precipice, the foot of
‘which is every where washed by a turbulent swell. These cliffs
are in a state of daily ruin, and their bases are beset with
enormous masses of rock which from time to time fall from them.
The rocks called Macleod’s Maidens, the islands in Loch Braca-
dale, and other detached rocks which skirt this coast, mark equally
the gradual waste of the land. But no slope is formed against
their faces, nor does any artificial shore accumulate at their feet,
except a narrow and almost impassable interrupted stripe composed |
of fragments. ‘The smaller pieces and the detritus of these larger
ones, are probably carried away from the coast by the incessant
action of the western swell far into the depths of the sea. As
there are no recorded soundings of this shore, I cannot confirm
this supposition by any account of the nature of the bottom. But
it will not be out of place to enter into a more particular detail of
this line.

The coast of Sky from Dunvegan head to the entrance of Loch
Brittle is, with but few exceptions, formed of high cliffs; variable
however in their altitudes as in their abruptness, but generally
very lofty and very abrupt, nay often precipitous and perpendi-
cular from their summits to the water’s edge, It is unnecessary to
note any but the most remarkable points, as there is a great general
resemblance throughout the whole. Between Dunvegan head and
Loch Bracadale they are often perpendicular, but variable in height,
and seldom attain the great elevation which they reach between
Talisker and Loch Eynort. There, as in many other places, they

Mineralogy of Sky. 21

possess a singularly striped appearance from the great variety of
colours in the several beds which compose them, of which twelve
or more may in different places be counted, all horizontal and
tolerably equal in their dimensions. The forms of these cliffs are
far too monotonous and too square to afford subjects for the pencil,
every part being marked by a general similarity of character. Near
the entrance of Loch Bracadale some variety is presented by the
three detached and pyramidal rocks called Macleod’s Maidens, the
highest of which appears to reach to about 200 feet. ‘This fea-
ture, of detached | pyramidal masses, is of frequent occurrence
on this coast, a remarkable perforated one being seen in Loch Bra-
cadale, and a similar one not far from Loch Eynort. They are,
like all other objects out of the ordinary course of nature, rather
singular than picturesque: the strange and the bizarre are seldom
legitimate subjects for painting, and rarely please long, after the
first wonder has subsided.

In Loch Bracadale some caves are found in the rocks, which have
no particular claims on notice either from their beauty, their mag-
nitude, or their singularity. Similar caves are of frequent occur-
rence between Talisker and Loch Brittle, the low projecting rocks
being also often perforated by arches which are sometimes exceed-
ingly complicated and remarkable. With the exception of some
projecting points of high rock the shores of Loch Bracadale are
flat, and this tract is among the most fertile of Sky. At its sou-
thern extremity the cliffs are perfectly vertical, and without that
slope at the foot, which so commonly accompanies the high cliffs
of trap, and which are so conspicuous in particular on the eastern
side of the island. The retired and green valley of Talisker opens
to the sea by a low beach, on which the natural embankment
already mentioned has. been formed by the western swell. Here

22 Dr. Mac Cuttocn’s Sketch of the

the cliffs again become high, and shortly rise to the greatest altitude
which they attain along the whole line of this coast. In a general
sense they may be called perpendicular, but they are seldom with-
out grassy slopes cither at their feet or in some intermediate parts,
which diminish their vertical appearance when seen in profile, al-
though when viewed in front they still appear perpendicular. The
outline is here more varied, the parts more numerous and intricate,
and the tone of colour more agreeable, while the foregrounds,
which are formed by some high and conspicuous detached rocks,
produce with them some of the most magnificent compositions of
rock scenery which are to be seen on the coasts of Sky. Not far
from this place is a large and very remarkable slide, by which a
considerable portion of the cliff has been brought from the summit
down to the shore, where it forms a promontory obstructing the
further progress of the mineralogist, who in defiance of toil and
hazard pursues along this rocky coast the beautiful minerals in
which it abounds. I have no measure of the heights of these
cliffs, but they are considerable. Comparing them with the masts
of passing ships I imagine that the highest can not be much less
than 800 feet. The cascades which fall over them are often dissi-
pated in spray before they reach the ground, or descend in a
mere shower of drizzling rain.

The cliffs continue with more variety of height than of cha-
racter to Loch Brittle, the habitation of the Osprey, and of, what
is more interesting to geologists, some rare minerals which I shall
describe in their proper places. At Loch Brittle the land runs out
into low projecting points, the interior being of small elevation
and disposed in terraces. The cliffs rise but little from this place to
the entrance of Loch Scavig, where the coast assumes a new cha-
racter, the declivities of the hills reaching the sea at a considerable

Mineralogy of Sky. 23

angle. Here the dark summits of the Cuchullin hills come in
view, and new features and new scenes arise to re-excite the interest
which so long an extent of an almost uniform character had suf-
fered to languish. : )

Loch Scavig is an inlet of the sea about a mile in depth, formed
by the Cuchullin hills, which rise with all their spiry and naked
crags high towering above it. At the bottom of this bay they
descend suddenly into the sea, brown and bare, with scarcely a
spot of verdure to enliven their dark sides, the only semblance of
life they possess consisting in the motion of the few cascades which
foam down their rugged declivities. Points of detached rocks pro-
jecting into the sea from their base, produce foregrounds for the
use of the artist, and relieve that intense depth of shadow which
seems ever to reign where the sun beams can scarcely find access.
But even the grandeur, the silence and desolation of this place are
forgotten, when in a moment on turning the angle of a huge rock,
the spectator enters on a scene which suspends the recollection of
all which had fascinated him before. He finds himself in a lone
valley surrounded by a wall of dark and naked rock, of which the
rugged summits are lost in the clouds, intercepting the light of day
and casting a twilight gloom over the seat of eternal repose. If
ever a sound disturbs this repose it is that of the wind which
whistles against the rocks, or of the cascade which rushes down
their sides ; if ever vestige of life is seen, it is the lone sea-gull
dipping its wing in the black still waters of Coruisk.* The valley
once closed behind the spectator, he sees no more its egress, and
calls to mind the tales of eastern fiction, where the victim of magic

* Coruisk, the water of the mountain hollow, not,Coriskin.

24 Dr. Mac Cuttocn’s Sketch of the

is for ever immured in some profound chasm of the mountains of
Caucasus. The lake Coruisk is rather more than two miles in
length, being fed by a powerful stream at its upper end, and dis-
charging itself into the sea by a wide and rocky channel, a
favourite resort of salmon. Its shores are every where covered
with huge fragments of rock detached from the mountains above,
and it contains two or three small islands which diversify in some.
measure the darkness of its surface. ‘The nakedness of the rocks is
not poetical. On the declivity of the mountain Garsven in par-
ticular, they rise from the base to the very summit, a height of at
least 3000 feet, in huge smooth sheets at a very high angle, per-
fectly bare and of a dark iron brown colour, not checquered even
by the growth of a single lichen or by one foreign tint to enliven
the uniform gloom of the surface. This rock seems indeed abso-
lutely inimical to vegetation, nor does it appear-to undergo the
slightest decomposition, or to admit of the formation of soil, the de-
tached fragments showing as little tendency to waste as the moun-
tain itself. Had the globe of the earth been entirely formed of this
rock it would still have been lifeless and void. It was among these
fragments that I observed a rocking stone of considerable size and
easily moved, having to all appearance fallen on such an edge as to
allow of the conditions required for producing this effect.

In quitting this scene, for which favourable weather is required,
since it is inaccessible by land, and the outer loch is subject to dan-
gerous and sudden squalls, little interest occurs on the east side of
Strathaird, except one fine example of a slide by which a large
mass of the hill has descended to the water. |

Having passed the point of Strathaird a succession of cliffs com-
mences which extends nearly to the end of Loch Slapin, formed of

Mineralogy of Sky. 25

aa

secondary strata, and of an entirely new character. Their upper
edge is generally even, and their faces quite perpendicular, but they
rarely exceed 60 feet in height. They are most remarkable for the
very extraordinary number of the caves which are found in them, .
and of the fissures by which they are intersected. These are rarely
_ of any great dimensions, but they are so numerous that they some-
times occupy nearly as much space in a given distance as the solid
parts of the cliffs themselves. I have counted twenty or thirty of them
in the course of a few hundred yards, the interstices having a re-
semblance to the ends of detached walls placed in a parallel manner.
They ate the consequences of trap veins which have been washed
away, but as they present important geological facts, I shall describe
them mote particularly hereafter. Few of these caves have been ex-
plored, but one of them has acquired historic celebrity from the cir-
cumstance of its having been among the numerous places of temporary
refuge inhabited by Prince Charles during his concealment. Another
has recently become the cause of great resort to Sky on account of
its stalactitic concretions, and itis popularly distinguished by the
name of the Spat Cave: it lies on the estate of Mr. Macalister, and
is too well known to require any more accurate description of its
locality. This cave is accessible from the cliffs above, for a short
time only at low water, but by means of a boat it may be visited at
any time in moderate weather, or with the wind off the shore. The
entrance is little less striking than the cave itself, and to the ad-
mirer of the picturesque it presents a scene even more attractive. It is,
formed by a fissure in the cliff, extending for a considerable way
and rising into high and parallel walls on each side, its gloom being
partially illuminated by reflected light, and its silence scarcely dis-
turbed by the wash of the surf without. A narrow and obstructed
opening leads unexpeetedly into the cave: hence for a distance of
VOL. 111, D

26 Dr. Mac Cuxtocn’s Sketch of the

about an hundred feet all is dark, wet and dreary, till we arrive at
a steep acclivity formed of a white stalagmite. Surmounting this
with some difficulty, the whole interior and ornamental part of the
cave comes into view, covered with stalactites disposed in all the
grotesque forms which these incrustations so commonly assume.
Lively imaginations may here indulge in the discovery of fanciful
resemblances, and the concretions have accordingly received names
more descriptive of the fancies of the spectators than of their real
forms. ‘The dimensions of the fissure are in this place but incon-
siderable, the breadth not being more than ten feet, and the height
scarcely exceeding twelve: it is not long however before the
height suddenly increases to forty feet or more, and a declivity of
perhaps thirty feet in length, from the surface of the stalagmitical
and cascade-like mount which forms the division between the sparry
and the dark part of the fissure, conducts to a pool of water occupy-
ing a space of twelve or fifteen feet in length, dividing the cave into
an outer and inner portion. The dimensions are here somewhat
enlarged, and the height in particular is much more considerable.
At a distance of about fifteen or twenty feet more from this pool of
water the stalactitical ornaments cease, and shortly after the cave
terminates, the whole length from the entrance to the end being
about two. hundred and fifty feet. However beautiful the interior
of the cave, from the white colour and ornamental effects of the
stalactites which incrust it, the want of sufficient dimensions mate-
rially lessens the interest, which in all other respects it is calculated
to excite. At the termination of the stalactitical ornaments there is
a dark descent for a few yards, filled with rubbish, the ruins of the
roof above, which being here naked as well as accessible, is plainly
seen to be one of the trap veins. ‘This vein is here about ten feet
wide, which is the general breadth of the cave itself, and it is easy

Mineralogy of Sky. 27

to see how by the wearing out of that vein the excavation has been
formed, having subsequently acquired its present degree of orna-
ment by the infiltration of carbonat of lime in solution. When
we consider the great depth of this cave and its distance at
present from the sea, we are inclined to inquire by what means
so extensive an excavation could have been formed, and how
the rock which has fallen from it has been disposed of. It is pro-
bable that the depth of water at the face of the cliffs was once such
as to allow of the ready access of the sea to them, and that at this
period the excavations so numerous on this shore were produced.
The subsequent accumulation of rubbish formed by its action, has
in later times produced the slope or shore which now excludes it
from further access, and protects the cliffs from further demolition.

In the little excavations which are found in the floor of this cave
we have the means of seeing the process by which the formation of
calcareous spar takes place, the crystallization being carried on in a
solution of the carbonat ‘of lime, precisely as it is in the saline so-
lutions in our laboratories. Ali these small pools are filled with
groups of crystals, in a state of constant augmentation, but of very
irregular forms. Doubtless these forms must be affected by the agi-
tation which the falling drops occasion in the solution ; and it is in
all probability owing to some circumstances of this nature, constant
in the same place but varying in different ones, that crystals of one
form are found to affect certain places, while in others they regu-
larly assume some other modification. As it offers no novelty to the
mineralogist, and belongs toa class of geological facts by no means
uncommon, it is unnecessary to enter into any further details
respecting it. Such are the principal circumstances which I had an
opportunity of remarking, and which appeared most worthy of notice
in the general face of the island.

yp 2

28 Dr. Mac Cutiocn’s Sketch of the

I shall now proceed to consider the nature of the rocks which
compose this island, in as regular a detail as my opportunities and
its intricate and unsettled geography allowed me to observe and
record them.

It was not without repeated efforts and much careful tracing of
the successions of the stratified rocks through coasts difficult in them-
selves and far distant from each other, that I was able to discover the.
key to the very great obscurity in which these are involved. It will
be seen that there are yet points unexplained, particularly respect-
ing the trap rocks, a circumstance which will not surprise geologists
who know that to patience, toil, and good seasons, must often ba
superadded good fortune; the casual discovery of perhaps the only
point over a wide tract which is capable of yielding the explanation.
of which we are in pursuit.

As the mica slate and its associate the quartz rock are the most
ancient of those which I have ascertained in Sky, I shall com-
mence from them as the foundation of the whole structure. I
have associated these rocks in this manner, because I have generally
found them. alternating, and bearing a common relation both to
those which appear to hold a deeper, and to those. which have a
more superficial position with regard to them, the granite and the
stratified rocks; but I need not repeat these reasons here as I have
discussed them at sufficient length in the account which I formerly
gave of quartz rock. I have not however traced any decided alter-
nation between these two rocks in this island, nor, as far as I have
observed, is it likely that any alternation will easily be traced, since
the beds of both are far less regular than is usual when they are as-
sociated in an alternating order. ‘The mica slate is found occupying
the district of Sleat, and it extends from the point of that promon-

tory to an irregular line drawn between Loch Eishort and Lock

Mineralogy of Sky. 29

Oransa, the point being much less accurately defined on the
eastern than on the western shore. The shores which it forms are
generally flat and shelving, but in some particular places, as at
Tormore, it rises into high cliffs. “The whole tract is: however but
little interesting, since the uniformity of this rock is only varied by the
occasional occurrence of veins of trap and of quartz. If I could de-
termine that the beds of mica slate hada regular position, I would
say that they were succeeded by quartz rock, and that this rock
terminated near Loch Eishort, being followed by a succession of
rocks to be described immediately; but to determine such a
succession, a regular disposition is indispensible, since, without that,
the uppermost in place may not always be the uppermost in order.
I must therefore content myself with remarking that the quartz rock
follows the mica slate im geographical position, and that its main
body will be seen occupying two hills which lie above Ord, from
which the skirts reach. to. the shores of the southern boundary of
Loch Eishort. The mica slate has no peculiarity of structure or of
aspect, such as to render a detailed description of it necessary, but I
think it proper to remark, that like many other districts of the wes-
tern isles which contain this rock asthe basis of their structure, it
is by no means so unmixed as it is generally met with in the exten-
sive tracts of it which occur on the main land: On the contrary, it
is frequently found passing into elay slate as well as into tale and
chlorite slates, affording an example like Arran, Isla, and Jura, of
the intimate geological union which subsists between these several
substances. Of the quartz rock I may remark that it is extreinely
compact, of a higlily crystalline aspect in general, and that its wea-
thered surface is so white as to render the hills which are formed of
it distinguishable at a great distance by their snowy appearance,

while at the same time it is frequently varnished, as it were, with the

30 Dr. Mac Cuxiiocn’s Sketch of the

same siliceous enamel which is so remarkable at Balahulish. In
most situations it contains the common admixture of felspar in
grains. Although not, strictly speaking, stratified, it bears the
marks of having once been regularly so, the beds having been ren-
dered obscure, partly by the infinite number of cross fractures
which it has undergone, and partly by the bendings and displace-
ments which it has experienced. At Ord indeed some extent of it.
is to be seen lying directly in contact with the beds of red sandstone
and in a conformable direction, and here the stratification is suffici-
ently regular to preclude all doubts, although the beds are not so
continuous and unbroken as those of the sandstone.

But I must not quit this district without noticing a remarkable
circumstance, uncertain as I yet am whether the observation was
correctly made or not. If I have not an opportunity myself to
verify or contradict it, I shall at least point it out to those who may
follow me through this country.

There is considerable intricacy as well as obscurity in the rocks.
which I have now described on the western side of the Point of Sleat,
although on the eastern there is neither variety nor obscurity to
contend with, this intricacy arising partly from the frequent occur-
rence of insulated portions of the secondary strata skirting the
shores, and of which the further details are cut off by the irregular
indentation of the sea line. Thus they become in a topographical
sense intermingled with the micaceous schist and with the quartz
rock in a very irregular manner, while the general confusion is
much augmented by the great number and perseverance of the trap
veins which traverse them. It is extremely difficult to find a way
through this geological labyrinth. It is near Gillan, where among
other places this confusion occurs, that the phenomenon in ques-

tion is to be seen: a bed of highly compact grey limestone contain-

: Mineralogy of Sky. 3l

ing shells is here included between two beds of quartz rock; un-
fortunately but a small quantity of the rock is exposed, and as’ it
lies low on the shore it>is impossible to trace the series to the
extent which is desirable. As far as I could conjecture the quartz
rock was a portion of the general series which alternates with the
mica slate: if this be correct it offers a solitary example of a rock
containing organized remains alternating with the series of mica
slate, a fact as yet so anomalous that it must not be received with-
out much more decided evidence than that which I have here
produced. I have to regret that the loss of these: specimens -pre-
vents me from describing the particular shells which I observed in
this limestone; yet doubtful as this fact appears even to myself, it
is somewhat countenanced by a circumstance not dissimilar which
occurs near Borrereg on the side of Loch Eishort, where the white
and crystalline quartz rock which alternates with the mica slate is
found in one place alternating for a short space with the blue lime-
stone and red sandstone, the two first and lowest members of the
secondary strata. With every wish to find that I had committed
an error in this examination I could not detect it, and must there-
fore suffer the whole to remain at present as I have stated it, an
example at least of a most deceptive geological appearance if it
shall not turn out to be an interesting fact.

The two associated rocks which I have here described are imme-
‘diately followed by a regular succession of stratified rocks which
I shall now proceed to detail; commencing at Loch Eishort, as
being the principal point in which I observed their contact with
the former, and from which I derived the clue to the order of suc-
cession of all the stratified rocks in Sky.

In distinguishing however the rocks which follow by the term
stratified, I am far from meaning to say that I consider the mica

32 Dr. Mac Cuttocn’s Sketch of the :

slate and quartz rock as unstratified, but their want of regularity in
the present instance, compared with the extreme precision and
order of those which follow, render the distinction convenient here
for the temporary purpose of describing them. I have in other
instances produced sufficient examples of the alternate and regular
stratification of quartz rock and mica slate to render it unnecessary
to say more on that subject: I have in the same places shown that.
these rocks alternate with clay slate, and my object at this moment
is to distinguish strongly the sudden change from great disturbance
to extreme regularity, which takes place here between two rocks
which in so many other instances seem to have undergone together
the common action of some disturbing force.

‘The first of these rocks is a compound series of beds consisting
of dark blue quartz rock interlaminated with thin layers of clay
slate of the same colour: these are to be found in immediate con-
tact with the white quartz rock, and in an order which is conform-
able to the general position of that substance where it is in contact
with them. Often the quartz of this rock prevails to the total exclu-
sion of the schist, and the beds are then much thicker than when the
chist interferes. They hold a remarkably even and straight course
for a considerable space on the north side of Loch Eishort, dipping
to the N.W. at an angle of about 30°. The thickness of this set
of beds appears to be extremely variable, but I know not that it can
be ascertained, since the excavation which forms Loch Eishort in-
terferes with the observation at the western point-of their exposure,
as the sea in that place covers the elevated edges, while in their
course eastward they become clothed with the covering of soil.

There is consequently a chasm in my attempt to trace their
extent eastward, but as the same rock appears on the eastern side
with all the same characters, and in the same position with respect

.

Mineralogy of Sky. 53

to the mica slate; I imagine no error will be committed if I con-
sider it as a continuation of this series.
This is the rock which forms the high mountains above the
Kyle ri’ch, which have already been mentioned in the general
description. The principal summits, on account of their elevation,
are visible at a considerable distance in coming from Glen Elg, and
they occupy the greater portion of that which may be called the
eastern promontory of Sky. Ben na Grien and Ben Ashlaig appear
to be the highest of the group: these decline into lower elevations,
and with some variation both of character and aspect till they dis*
appear, but I have to regret that I can give no account of the con-
nections of either of the outer extremities with the neighbouring
rocks. It is too common for the geologist in the course of his
labours to find that he has commenced at the wrong end of his in-
vestigation, and to discover, when it is too late to profit by it, that
he has probably found the solution of his previous difficulties when
the difficulties themselves are no longer accessible to him: I can
only therefore offer it as a conjecture, that the rock which forms
the mountains in question is a continuation of the one already de-
scribed at Loch Eishort, since its examination unfortunately pre-
ceded that of the latter, and it was out of my power to resume
it when I had obtained the information which would probably have
enabled me to speak decisively concerning it. I would recommend
to those who may follow me to trace it with care from Loch
Eishort to the eastern shore, by which proceeding they will pro-
bably succeed in determining ‘that which I am compelled to leave
in doubt, but I may nevertheless describe its leading features. It
is by no means regularly stratified, nor is it possible to trace for any
considerable distance even the fragments of a regular prolongation
of the edges of beds, such as is so distinctly exhibited in the quartz
VoL. 11. E

34 Dr. Mac Cutrocn’s Sketch of the

rock of Jura; yet there are evident marks of stratification, which
in many places are sufficiently regular and extensive to justify the
belief that it has once possessed a greater degree of regularity and
extent, which have been disturbed by subsequent changes. The
predominant colour is a bluish or greenish grey, and its most
general aspect that of a compact splintery quartz, often obscurely
granular, and every where traversed by veins of ordinary white
quartz. At Kyleaken it has a brown colour and a fat appearance,
but becomes white and harsh on exposure to the weather, in con-
sequence of the decomposition of the felspar which it contains.
The great thickness of the mass here, compared with the thinness
of the similar rock at Loch Eishort, is no proof of non-identity,
since in so many other cases we find strata differing, in perhaps as
great a degree, in thickness where we have the most satisfactory
evidence of their continuity. I have not observed this rock in any
other part of Sky, and it will presently appear that it could not be
expected any where but beneath the sandstone near Loch Scavig.
I shall not be surprised if it exists at the southern side of Soa under
the sandstone beds, since that is its place, but this part of that island
was unfortunately the only one which I could not reach. That it
is a bed of great extent in this country, although so little visible, is
confirmed by its being found in Rum, and in the same position, as
I have ascertained.

The rock next in order to this is the red sandstone, and the
connection between the two is equally distinct at Loch Eishort,
where they are found following each other in a regular order and in
intimate contact, there being indeed a gradual passage from the
blue quartz rock into the red sandstone by a. series of intermediate
changes both in point of hardness and colour. The same transition
will be found near Kyleaken on the eastern side, although I cannot

Mineralogy of Sky. 35

point it out so distinctly. The certainty of a transition between
these two rocks is equally well marked by another circumstance,
although that indication does not appear at Loch Eishort; namely,
by the alternation of the beds of schist with the red sandstone,
a phenomenon to be observed at Loch Scavig, as I shall presently
show. Following this sandstone it is to be seen forming a con-
siderable part of the hills which rise on the northern side of Loch
Kishort, and extending along that shore as far as the farm of
Borrereg where it ceases. The beds succeed each other with
great regularity, and are of considerable thickness; as far a&
I should judge from a rude estimate formed by comparing the
measures of their edges with the space which they occupy,.I should
imagine that the collective mass does not here fall much short of a
thousand feet in thickness, tallying in this respect very nearly with
the dimensions which it seems to maintain in Rum as well as in
Soa, both of which I have no doubt are different portions of the
same rock. .

This red sandstone is also found skirting the southern shore of
Loch Eishort in different places, and is particularly conspicuous at
the castle of Dunscaich, a building of no high antiquity, but
"situated on a rock, the traditional residence of Cuchullin “ King
of the Isle of Mist.” This position is readily explained by observ-
ing that the line of Loch Eishort crosses that of the direction of the
sandstone in an oblique manner, leaving thus a portion of it on the
southern shore; it is here often in contact with the white quartz
rock, the intermediate blue rock having disappeared. From this
I should be inclined to suspect that there is a real chasm between
the conjoined rocks consisting of mica slate and quartz rock, and the
stratified ones now under review, how much soever some of their

portions may appear consecutive. I have pointed out at some
E 2

36 | Dr. Mac Cuttocn’s Sketch of the

length in other places the errors that may arise in these observations,
and need not enter largely into the question in this place, but it
appears to me a sufficient argument that two sets of rocks are not
consecutive if those which correspond in one place do not also corre-
spond throughout. I should expect to find that the same bed of
red sandstone exists between Kyleaken and Broadford, where I had
no opportunity of looking for it ; but beyond that it is not likely to
occur, as the limestone which lies at some distance above it in the
order of superposition occupies the lowest situation on the shores of
Broadford. I mentioned that the same bed is to be found at Loch
Scavig, where it is plainly connected with the very large mass of simi-
lar sandstone which constitutes the main part if not the whole of the
island of Soa; it occupies here the lowest visible situation, being
washed by the sea and exposing but an inconsiderable thickness,
since it is shortly followed by the trap, when it finally disappears,
none of the subsequent stratified rocks which accompany and follow
it near Loch Eishort being here found. It is here interstratified
with beds of a schist which has sometimes the character of fine clay
slate, while at other times, the lamine being separated by coarser
particles of sand and of mica, it puts on the character of that which
has been called fine graywacké slate. I have on other occasions
shown* that these rocks are not necessarily distinguished in posi-
tion, and that near Loch Ard in Perthshire, and Crinan in Argyle-
shire, the several sorts of clay slate and graywacké are irregularly
intermixed: the same phenomenon is to be seen in many other
parts of Scotland, which I cannot here pretend to enumerate;
although the question is of importance to geology, this is not
the place in which it must be discussed. The fact abovemen-
tioned however extends our objections to the commonly received

Geological Transactions, vol. 2d.

Mineralogy of Sky. 37

*

2.

arrangement even one step further, since I have shown that perfectly
characterized clay slate is here a member (to use the Wernerian
language) of the flectz rocks; the sandstone here described being
analogous to the old red sandstone of that school, and a member of
a continuous series of stratified rocks, of which the uppermost con-
tain shells and other undoubted characteristics of their rank in the
‘order of rocks.

. The extent of this rock on the shore is not great, but it may be
seen occupying a continuous line both on the shore of the sound
of Soa and within the entrance of Loch Scavig, forming the foot
of Garsven, one of the highest of the Cuchullin group.

These are the only places in which I have found this rock, and
I have no great reason to expect that it will be found any where
else, as its dip does not any where indicate its probable re-appear-
ance; yet I should not be surprised were it to come out at Loch
Sligachan, since the limestone which immediately follows it in
regular order is to be seen there. ‘These beds, the limestone on
_ the one hand and the quartz with schist on the other, will be guides
to those who wish to search for this rock in other parts of the
island.

The mineral character of this sandstone is very uniform; it is
most commonly of a red colour, but it becomes brown or grayish,
when in the neighbourhood of the schist, and sometimes even
partakes of the blue colour of this substance. It is of a moderately
fine grain and very tractable as a building stone, sometimes possess-
ing the softness of an ordinary sandstone and at others acquiring a
flinty kind of hardness, more particularly when it approaches the
schist. It is generally mixed with clay, or is of an argillaceous
nature, and in some places moreover it is found to contain particles
of calcareous matter: in some few places coarser portions are to be

38 Dr. Mac Cuttocn’s Sketch of the

found, formed of large gravel or even of fragments, but I have not
seen either in Sky, in Soa, or in Rum, any regular beds of conglo-
merate connected with it, although I have in these situations had
repeated access to the whole thickness of the rock. Although the
general colours of this rock are such as I have described, yet it
seems occasionally, like the lowermost red sandstone in other places,
to contain portions of a different complexion ; one portion of such
a bed is seen under Garsven opposite to Soa, where it is of a white
colour and intermixed with decomposed felspar, yet still exceedingly
compact. Pebbles of quartz and granite are imbedded in some of its
lamine. For the sake of those who contend for the doctrine of
universal formations of rock, I have recorded the whole of its cha-
racters and connections that they may have opportunities of com-
paring them with those of other similar rocks, and I can only add
to what I have here said, that as I imagine Rum and Sky to contain
portions of one common bed, so I am inclined to think that the
red sandstone which I have found on the western coast of Scotland
in various places, from Loch Ewe to the Ru Storr, appertains to
the same series of beds. It is still the same sandstone, as I imagine,
which extends to the east coast and finally to Orkney.

The next bed in order is a bed of limestone, the investigation of
which was attended with more labour and doubt than that of all the
other rocks of Sky, and of which the history I am about to give
cannot appear less credible to others than it did at first to myself: the
demonstration which I at length procured and shall now lay down is
however such as to admit of no dispute. It is important in a
general view since it shows us how little reliance can be placed on
internal characters in assigning the positions of rocks in the system,
and since it may possibly lead the way to the explanation of those
anomalous limestones to which the examples occurring near Ply-

Mineralogy of Sky. 39

mouth, and as yet involved in so much obscurity, may perhaps be-
long, and which have been ranked in the class called transition by
the Germans, since they were supposed to be of higher antiquity
than the secondary or /loctz strata of the same school. This bed is
found at Loch Eishort immediately following the sandstone, with
a common dip, and in every respect perfectly conformable to it.
“It is readily distinguished wherever it occurs, provided its upper
surface be exposed to the weather, and this at very considerable
distances, the appearance which it here puts on being that of detached
and irregular masses with a deeply honey-combed surface, the
cavities being from a foot to two in depth, rounded and perpen-
dicular, while the projecting portions are equally rounded and
smooth. No lichen attaches itself to that surface, but whatever its
hue be, it weathers to a bluish colour, by which it is visible among
all the surrounding rocks. I could find no means of ascertaining
its thickness at Loch Eishort, but near Kilbride where it is fairly
exposed it is some hundreds of feet thick; I have however reason
to imagine that this dimension is very variable. It may be traced
where it first appears at Loch Eishort from the point where it is
in contact with the sandstone, for a considerable way up the hills in
the direction of Broadford, but is at length lost amidst trap and
syenite, and amongst the mossy and deep soil of this rough ground.
Pursuing the line of shore it shortly disappears, other beds coming
in the way which will follow next in the order of descrip-
tion; but it is recovered at Kilbride, and hence may be traced
through the remainder of its connections to the no small surprise
of the geologist. As the sandstone bed does not exist at Kilbride
the identity of the limestone cannot here be proved by that of the
beds on which it reposes; instead of sandstone indeed its lower
surface is found in contact with the syenite already generally

40 Dr. Mac Cuxnzocn’s Sketch of the

described. The absolute identity of its aspect, composition, and mode
of wéathering, might perhaps be sufficient to prove the identity of
its nature, but this is put out of all doubt by finding that it is here
followed by the same set of beds which succeed to it in that place
where the sandstone precedes it, and of which the continuity can
be traced between the two points. The drawings (Pl. 2. fig. 1.)
which accompany this paper, will explain better than words this
very essential circumstance in the geological history of Sky.

There is here an opportunity of tracing by a very perfect natural
section the change which it undergoes between the very regular
beds which lie near it on the one hand and the irregular surface of
syenite with which it is in contact on the other. At this surface it
bears no marks of stratification, but is an irregular and almost shape-
less mass, while near the former beds, which also consist of limestone,
it becomes first vertical and gradually more regular, till at the end its
general bearing, although much deformed by counter fissures, partakes
most decidedly of the general inclination of the stratified rock, which
is here about 25°. In geographical distribution it may be here traced
in two divisions, separated from each other by syenite and inter-
sected by trap veins, both of these divisions extending towards
Broadford and uniting into one scattered and irregular mass about
three or four miles short of that place. The uniformity of its
character, as well as its continuity throughout this tract, is such as to
leave no doubt that the marble of Broadford already mentioned,
and which I shall hereafter more fully describe when I speak of
individual minerals, is a continuation of this portion of the limestone
beds. When it has once quitted the sandstone that-rock is no longer
seen, but the whole remaining portions of the limestone, occupy-
ing a great space from the hills which skirt the eastern side of
Strath to the foot of the syenite mountains on the opposite side, is

Mineralogy of Sky. 4]

(always with the exception of whin dykes) in contact with syenite ;
this contact ean be distinguished in many places at the surface, and
it has moreover been brought to light in the excavations which
have been formed at the marble quarries; it is so intricate that the
limestone is often divided into insulated portions surrounded by
syenite, and were it not for the clue which is given by the shores

‘at Kilbride the whole tract is so obscure that it would have remained
as unintelligible to me now as it did in the first examination which
I ‘made of it. It is too speculative an inquiry to consider what
influence the syenite may have had in producing this irregularity ;
nay I have not even the means of proving that the syenite is pos-
terior to the stratified rocks ; but in the course of examining that
rock hereafter, I shall assign reasons for supposing that this is
really the case, and that like the trap rocks to which it is associated
it is not improbably the cause of all the irregularity apparent in
this place. |

If even the shadow of a doubt could remain respecting the
connection of this, which I shall distinguish by the name of the
marble limestone, with the shell limestone, it is removed by the
discovery of a regular alternation of the two near the farm of
Borrereg, a sketch of which (PI. %. fig. 2.) is introduced into one
of the sections designed for the illustration of these rocks.

The limestone having completely lost all semblance of stratifica-
tion where it is involved among the syenite, is found forming large
insulated lumps, of which the great structure and general fracture
resemble that of the Devonshire insulated limestones, and those of
Assynt which I have described in the Geological Transactions, vol. 2.
It is fissured in various directions, and can be raised in large irregu-
lar blocks only. Hence it has very naturally been considered as a

primary limestone, an error into which I was at first inclined to
WVOL..101. F

49 Dr. Mac Cutrocn’s Sketch of the

fall myself. This is confirmed by its texture as well as its colour,
both of them resembling those which are supposed to be charac-
teristic of primary limestones. In these respects indeed it possesses
an exact resemblance to the limestones which we find in various
parts of Scotland associated with schist, gneiss, and granite, of
which I have recorded examples in different places. From this, as
I have already hinted, we ought to receive with distrust any
attempt to distinguish the primary and secondary limestones by
internal characters, nay even by their external forms, since in this
respect also the limestone of Strath bears a perfect resemblance to
the primitive limestones already alluded to. The texture of this stone
is almost every where compact, with a fracture finely granular in
the surface, and varying between the splintery and conchoidal. It is
generally brittle, a character rare in the stratified limestones, and in
many places even breaks with the violence and cleanness of silice-
ous schist. In its chemical composition it is generally pure; but
where in contact with the syenite or the trap veins, becomes over-
loaded not only with silica but with magnesia and argil also. In
such situations it often contains veins and nodules of greenish
transparent serpentine, and adopts a variety of colours, a circum-
stance in which it also resembles most exactly those limestones
which in Glen Tilt are found in contact with granite, or at Bala-
hulish, and in Tirey and Iona with mica slate and gneiss. The predo-
minant colour is grey, varying from nearly white through all shades
of dove colour to a dark blue grey, sometimes beautifully striped,
and mottled or veined; in many situations it is of a pure snow
white, forming a perfect variety of statuary marble, which I shall
have occcasion to describe more particularly hereafter, and affording
as yet perhaps a solitary instance of this variety of limestone oc-
curring among secondary strata. When I say a solitary instance, I

Mineralogy, of Sky. 43

must however add my suspicions, that when more attention shall
hea been paid to geological investigations, many of the facts which
I have enumerated in various parts of these papers will not appear
either so solitary or so extraordinary as they now seem.

_I have shown that this limestone is in contact with the syenite,
and. it is also in contact with trap, since a hill of this substance is
‘found surmounting as well as interfering with it near Loch Eishort.
I might therefore proceed to describe these rocks according to the
order which I have adopted; but nothing certain is as yet known of
their real places, and. if, as I imagine, and as I think will appear
not only here but on almost every occasion where I have described
them, they intrude among the regularly stratified rocks, it will be
better to defer. the consideration of them, as I have done on other
occasions, to the last. Before however finally quitting this lime-
stone I must not omit to mention that a similar one is found occu-
pying the south side of Loch Sligachan in a similar manner, and
that it has in all probability the same origin and connections, al-
though I had no opportunity of investigating it to my satisfaction.

_ Returning to the original point at Loch Eishort we find the.
series of beds which follows this limestone in contact with it.’ At
the very point of contact there.is an interference of the two sets,
which is highly, satisfactory, as tending to establish: their perfectly
consecutive nature, and consequently of determining the place of
the former. limestone without the shadow of a doubt. Where they
meet, two or three laminz of the uppermost limestone alternate
with an equal number of the lower one, and they are readily dis-
tinguished, because the upper ones being mixed with schist have a
superior degree of permanence, and project with a sharp edge on
the vertically corroded sides of the subjacent one. The upper
limestone is equally to be seen.following the under one at Kilbride ;

FQ

44 Dr. Mac Curiocn’s Sketch of the

but the same interference is not visible there, although the paralle-
lism is perfect.

From either end of this junction the limestone beds of the
upper series may be traced all round the point which separates
Loch Eishort from Loch Slapin, intersected every where like the
former by trap veins. Neither the thickness, the number, nor
the order of these beds can be ascertained, as they are much too
complicated and difficult of access to admit of such an examination.
The very attempt would be a superfluous endeavour after accuracy,
since enough of them is ascertained to prove that only which is
important to be known, the order of their connections with the
neighbouring rocks, and the characters by which they can be iden-
tified with more distant strata. In general they are formed of thin
and thick laminz, composed of a dark blue earthy limestone, ‘at
times somewhat more crystalline, and variously interleaved with
argillaceous schist of various dimensions. These beds, like the
former, are inclined at an angle of about 25°; they seem most re-
gular as well as thickest at the point of separation between the two
Lochs Eynort and Slapin, while near the very same place they are
also found in very thin schistose laminz, so that I imagine there is
no rule to be laid down respecting them; they are found occu-
pying the island of Heast, as well as a‘long ridge of rocks which
here intersect Loch Eishort ; and they. may also be traced at Ord,
and further down this shoré’ even‘as far as Gillan, following the
red sandstone, for the same geographical reasons, probably,’ that I
assigned when speaking of that substance. Here however the
intermediate bed, that which contains the marble, is deficient, and
we have already seen that the blue quartz and schist are also de-
ficient, so that the order is heré mica slate, red sandstone, schistose
limestone ; instead of mica slate, blue schist with- quartz, red

Mineralogy of Sky. 45

sandstone, marble limestone, schistous limestone, two important
members having disappeared in so short a space. This is the only
instance which has occurred to me in Sky of discontinuous strata,
since the Western Islands exhibit but few examples of this class of
rocks, and I am glad to have an opportunity of mentioning it, as
I am convinced that such discontinuities are common in nature,
‘and that great errors have been the result of the fondness with
which geologists have pursued through viewless regions of the
earth, continuities of | strata, and universal formations. But to re-
turn to the upper limestone. It is often remarkable for the ca-
vernous and corroded aspect which it assumes where in contact
with the sea, which arises from the falling out of the shells which
st’ contains. The beds are numerous but irregular, and the shells
themselves vary much in quantity in different places. I could find
only three species, a gryphite, an ammonite, and a cardium, nor do
I know whether more are contained in them, since but few of the
numerous beds are accessible.

It is now necessary to attempt the tracing of this bed in other parts
of Sky, and I imagine that this can be done to a certain extent.
This examination might have been rendered more complete by myself
had I commenced the survey of the island in the reverse order to
that in which I have described it, being guided for want of a
better reason by mere geographical convenience. Hence the re-
marks on the distant and solitary fragments of strata, made when
there was no prospect of connecting them, are less perfect than
they would have been, had I commenced the survey where I have
now commenced the description, and they are insufficient for
assigning their general connection. Since however the strata of
limestone found at Broadford contain the same animal remains, I
have no doubt that they are portions of the same strata, and that.

46 Dr. Mac Cuttocn’s Sketch of the

the beds of this substance, which are visible along various points
of this shore as far as Sligachan, are equally continuations of the
shell limestone, more particularly as the marble limestone is also
found at Sligachan in that position in which it might be expected
with respect to the former, But I can give no clue to the history
of the limestone which is entangled among the trap to the north of |
Broadford, having neglected to make such an examination of it as
would have been required for this purpose. I must trust to some
future geologist for the completion of what I have left unfinished.
The most remarkable of these unascertained beds is found to the
north of Portree, far inland, and extending towards the Storr on
the eastern declivity of that range of hills, being interposed among
enormous beds of trap. Others may be seen in various positions
accompanying the secondary strata which lie under the trap on
the shores of Trotternish ; but as I can not pretend to give such a
geological description of them as would satisfy myself, I must be
contented with this cursory indication of their localities. I have
little doubt that with the clue which I have now furnished, the
task of assigning their geological relations will be found easy.

I find some difficulty in continuing the pursuit of the stratified
rocks upwards from Loch Eishort, because a great geographical
chasm now takes place between those already described, and the
next most extensive mass which forms the promontory of Stra-
thaird, and because they are connected but by a small indication of
their order of succession. In the general description I have noticed
that the rocks of Strathaird consisted chiefly of sandstone, alter-
nating with thin and rare beds of limestone: these I conceive to
be the next in order of superposition, and the proof rests on this.
At the point which separates Loch Slapin from Loch FEishort
a series of sandstone beds is found following the limestone lately

Mineralogy of Sky. 47

described, and evidently in a higher situation: it is a calcareous
sandstone, and bears a precise resemblance to that which consti-
tutes the whole of the eastern side of Strathaird. Now as no sand-
stone of this description is found among the. lower beds, and as
we have clearly traced the order of those from the mica slate to
this point, I think that we need not hesitate in placing the sand-
stone of Strathaird in the situation which I claim for it, the last in
the series of the secondary strata. However that shall be de-
termined, I must proceed to describe it. It is to be seen reaching
from the termination of the trap on the western side of the pro-
montory, round the point of Aird to nearly the upper end of
Loch Slapin, preserving a great evenness of direction and con-
" sistency of character throughout this space. I have called it in
general a sandstone, although it will be seen that it also contains
beds of limestone, but in small number and quantity. The po-
Sition of the leading line of these beds is so generally horizontal
that it is never found to vary five degrees, and that variation is
so gradual that it will often pass without notice: but it is at-
tended with a disposition so remarkable, that I think it neces-
sary to point it out, and as it is difficult to render it intelligible
in words, I have added a diagram* for illustration. Each
bed seems compounded of two parts, the one a single horizontal
lamina, and the other a series of inclined ones, or, there is a re-
‘gular alternation of a set of inclined laminz with one horizontal
one. ‘These are perfectly defined, since the intervals are deeply
channelled by the weather, the whole having the aspect of some
of the carved ornaments of Saxon architecture. This appearance
gives on a first view the impression as of a regular series of beds,
alternating with each other, of which the one is horizontal, and

* Pl, 4. fig. 1.

48 _ Dr. Mac Currocna’s Sketch of the

the remainder in an unconformable position to it. But it must
rather be considered as the indication of an internal structure, of.
which however all marks disappear when a fracture is made,
a case analogous to what occurs in’ basalt and many other
rocks, of which the internal structure is so often detected by the
changes which they undergo on exposure to the weather. A
similar case, which I have observed in the argillaceous schist of
Isla, serves to confirm this explanation. The appearance in this
instance is so precisely like, that the same drawing will serve to re-
present both, and the nature of the cause is amply confirmed in
this, that while the beds of the schist are apparently divided in the
direction marked by the horizontal lines, they are fissile only in that
which is marked by the oblique ones. It hence also follows, that
if the fissile property of clay slate is the result of some internal
arrangement analogous to crystallization, we are equally entitled to
attribute the structure of this sandstone to the same cause. The
inclination of the oblique laminz upon the horizontal ones varies
from ten to thirty degrees; but it is regularly in the same
direction, the dip, if it may be so called, being to the south.
This appearance is neither rare nor dubious, it is extremely well
marked, and predominates throughout the whole range. The
measurement of the parts having been mislaid, I speak from recol-
tion when I say that the intervals between the horizontal lines
vary from one foot to a foot and a half. There is no difference in
the quality of the two sets of laminz, both are of white sand-
stone, generally more or less calcareous.

To enter more minutely into the composition of these beds, let
me now remark that the sandstone often acquires the aspect of
some of the most compact and crystalline varieties of quartz rock,
while in other cases it has the lax texture of an ordinary freestone.
In some places it is calcareous, and the calcareous matter varies so

Mineralogy of Sky. 49

much in quantity that the compound would sometimes be called a
calcareous sandstone, while at others it would be described as a si-
liceous limestone. In the latter cases it is often dark-brown, gray,
or even of a dark lead blue. The beds of mere limestone are
rare, and those which I observed lie towards its upper boundary ;
they are of considerable size immediately in the vicinity of the
Spar cave, which I described at the commencement of this paper.
I think they are much more generally granular than compact,
and some of them indeed resemble an aggregate of rounded grains,
of the size of mustard seeds, not much differing from some of the
oolites, but more compacted, and generally containing, besides
these grains, crystallized platy particles. These strata are inter-
sected ina remarkable manner by trap veins; but I shall defer
the consideration of those to that which I conceive their proper
place, the last in the history of the rocks.

The geographical chasm which interferes between this and the
remaining portions of white sandstone found in Sky is such, the
want of accompanying strata so general, and the absence of cha-
racteristic indications in the internal composition so great, that I
feel quite unable to determine the nature and connections of these
detached portions. If any thing can be drawn from such indi-
cations as they present, they seem rather to prove that the sand-
stones which are found at Portree and in the northern parts of the
island, appertain to strata different from those last described ; but
the remarks I have already made on the discontinuity of the lime-
stone and the blue quartz rock, render me diffident in admitting
any evidence respecting continuity of stratification, or the reverse,
without access to proofs of a more decided nature.

White sandstone is to be found in many places on the eastern
coast of the island, and is readily visible at Portree, where it alter-

Vor. m1. G

50 Dr. Mac Cuttocn’s Sketch of the

nates with the trap in the same manner as it does in Egg; and in
this neighbourhood it also exhibits the same appearance of glo-
bular concretions which occur in that little island. It also is found
in several places, containing globular masses and fragments of trap,
such as are frequent in the similar sandstones, which are seen on the
opposite coast of Raasa. The same appearances continue along the
shore to Camiskanevig ; and although I did not approach the land
sufficiently near to be certain of the fact, I am inclined to think
that similar arrangements exist all the way to the Altavig islands.
Sandstone is found moreover on the eastern side of Loch Snizort ;
and, I may add, generally on the western shore of Trotternish, par-
ticularly at Duntulm, where it contains shells, of which, for the
reason mentioned in speaking of the limestone, I neglected to take
a sufficient note, not being aware that they might be of future im-"
portance in my researches. Here however it alternates with shale ;
and, unless I am mistaken, with very thin laminz of coal, such as
occur in the sandstone of Egg, while it also contains imbedded
fragments of charcoal, and I am therefore inclined to think on
these indications, that this sandstone belongs to a deposit still su-
superior to that of Strathaird, and probably the same as that
which is found in Egg. The last white sandstone which I met
with was in Glamich, where it was penetrated by veins of trap
and mingled with the mass of the hill, but the space I saw exposed
was so very small that no conclusions could be drawn from it.

I must not terminate the description of these strata without pointing
out a circumstance of importance which might otherwise escape
the reader’s attention, namely, the conformity of all these rocks. I
will omit that conformity which in some places appears to exist
between the mica slate and quartz rock, and the incumbent ones,
because it is certainly incomplete; but between the bed which
consists of blue quartz rock and slate, and the red sandstone, it is

.

Mineralogy of Sky. 51

complete, and consequently the same for the whole way upwards.
Now in our system of geology, not only is this sandstone con-
sidered the first of the secondary strata, but the schistose rock is
ranked among the primary or among the ¢ransition; and the difficulty
will be equal which ever term we adopt. If the nature of the
sandstone did not determine its rank, its place after the schistose
rock would be sufficient for that purpose : so that here the primary
and secondary strata are not only following in conformable order,
but that order is demonstrably not accidental as in Mull, where an
instance of this nature occurs, since there is a perfect interference
and alternation of the two at the point of contact. Those rules
therefore, which would define the secondary rocks by their want
of conformity to the primary, either have not selected the first of
these primary rocks as their basis, or, the law of non-conformity and
of a thorough separation between the two classes is exceptionable.
Having thus as far as is in my power described, according to their
superposition, the rocks which seem to follow in the most regular
order, I shall proceed to describe those which are uppermost, the trap
and syenite, which will complete the account of the rocks of this island.
In naming these as uppermost, I am far from meaning to say that
they are exclusively so, as I shall on the contrary show that they
also penetrate the superior strata. No distinct position can in fact
be assigned to rocks which are not stratified, and such are generally
granite andtrap. These unstratified substances interfere with almost
all the regularly placed rocks. Although granite is not indeed found
passing through or lying near the primary stratified rocks, unless in
the form of veins, yet it bears no regular relation to them, and is
occasionally found in the same place, in contact with every indivi-
dual of a series of different stratified substances. The other un-
stratified rocks, trap and syenite, bear a still more intricate relation
G2

52 Dr. Mac Cuttocn’s Sketch of the

to those with which they are connected, since they interfere not only
with the primary ones, but with almost the latest of the secondary,
and are frequently found lying indifferently both above ard
below these latter. Hence have arisen distinctions which are often
merely nominal, and founded on false theoretic views, of traps of
one or other age, of first, second, third, and newest formations.
The same identical mass will often possess the characters of all these,
since it will in one place be found incumbent on the latest, in an-
other on the most ancient rocks. Except this, I know not that any
certain marks of distinction can be pointed out among the several
traps. In the greater number of instances at least which have
fallen under my examination, such a relation between an unstra-
tified rock, occupying the irregular and uncertain position which
trap does, and those regularly stratified ones which maintain a con-
stant order of succession, is by no means a criterion by which to
judge of its ‘relative order with regard to these. The aid of a diagram
is perhaps required to render this statement intelligible to those who
have not examined the rocks for thetmselves.* The same mass of
‘trap will be found in one place incumbent on clay slate, in another
‘on red sandstone, in a third on shelly limestone, in a fourth on the
‘uppermost secondary strata. In such a case when the separate por-
tions are either not all accessible, or when they lie far distant and
interruptedly, we might be easily led to conclude that they were-so
many distinct deposits, and thus apply to them terms derived from
the particular beds with which they were found immediately in
contact. A more intimate acquaintance with them, and with the
general nature of trap is required to correct these‘erroneous conclu-
sions, and the accompanying* sketch, will éxplain that which ac-
tually occurs in nature, and of which, if I mistake not, instances are

* See Pl. 4. figs. 2 & 3.

Mineralogy of Sky. 53

to be found in the very island of which I am writing, as well as in
many other situations in Scotland. Ido not however mean to deny -
that instances exist where a real distinction of periods in trap
rocks can be proved, and I have myself observed some which I
shall perhaps have occasion to describe at a future opportunity. I
am only desirous to enforce on geologists the necessity of drawing
their distinctions from real and not from theoretical views, and of
establishing criteria which are better founded, and which rest on
more satisfactory evidence than that produced by the mere apparent
or even real superposition of an unstratified above a stratified rock.
I am even inclined to think that at least two very distinct formations
of trap are to be found in the western islands of Scotland, but I
cannot discuss the proofs in this place, as the island of Sky has not
as yet produced sufficient evidence of them to satisfy me.

Amid the doubts which prevail in the minds of others, the pre-
judices derived from early habitude with erroneous systems, the
natural obscurity of the subject itself, and the extremely inaccessible
natute of these rocks, I find it difficult to preserve a consistency in
the account which I shall give of them, and to render the details of
the history of this family of rocks so distinct, as I am confi-
dent it will hereafter turn out to be when the subject becomes
better known, and when nature shall have been examined by a greater
succession of real observers, who, however desirous of supporting
systems, are still more anxious for truth.

In commencing the account of these rocks the’ trap* and the

* T think it necessary to say that I have throughout used the term Trap as the name of
a family, including basalt, greenstone, tuff, amygdaloid, trap porphyry, and many
other varieties of rock which have as yet obtained no names, and which constitute a class
equally distinguished by their geological as by their mineral characters. I have preferred
it because as it is derived from the external outline so common and characteristic of this

54 Dr. Mac Cutiocn’s Sketch of the

syenite, I must premise that I have not found in Sky any indication
to denote the relative order of the two. If indeed they are both ir-
regular substances, as I think there is no reason to doubt, any pri-
ority or posteriority is out of the question, or at least it cannot be
ascertained by examining their juxtapositions. Ifthe one set were
proved to be constantly superior to one set of stratified rocks, and the
other to a different and later set, the question of rank: might be
settled between them: but these connections are difficult to ascer-
tain to a sufficient extent, and possibly none such exist. If one stra-
tified rock is in one place superior to another, we are sure that it is
every where superior ; but if we have ever so clearly proved that a
body of trap or of any other unstratified rock is superior and in con-
tact in one place to any given stratum, we have no certainty that it is
equally so every where. Thus I shall in this island show that the
trap rests in one place on the latest sandstone, in another on the
earliest. No means therefore are offered here of determining the re-
lative order of these two unstratified rocks, but I have little doubt
from the phenomena which I have witnessed in Rum and Mull, that
they are both portions of one irregular mass. I shall therefore com-
mence with the trap as the most extensive.

I was once inclined to make a distinction between the trap which
forms so large a part of the Cuchullin hills, and that which is found

class of rocks, it is in no danger of misleading by producing any confusion of individuals,
and because it was already in use as the name of many in this family without having been
rigidly limited to any one species. I have also chosen the term syenite as the generic term
of a set of rocks generally allied to these, and which had already been applied to that
rock by Werner, excluding from this denomination the original and classical syenite, which,
as well in geological connection as in mineral character is a mere modification of granite.
The compound term syenitic granite may be applied to this, as I have remarked in a former
paper. Varieties intermediate between common trap and syenite may be called syenitic
trap.

Mineralogy of Sky. 55

eccupying the great mass of the island, from the difference of their
external characters and form, and from the existence of some par-
ticular varieties in the one, which are not found in the other: but
I have not the means of drawing this distinction, nor of saying
where or how they are connected or disjoined. I have little doubt
that there are distinct deposits of trap rock of different periods,
‘as well as that there are veins of the same; but whether these
two leading divisions in the external appearance of Sky are also
distinctions in the geological xra of the rocks which form them,
is more than I can determine, since they have no distinct set of
connections by which such a supposition could be verified. Further,
when I attempt to trace their connection with each other, I ima-
gine that I can every where see the mountain trap of the Cuchul-
lin, blending with the stratified trap of the coast; and this opinion
is confirmed by every thing which I have observed in Mull, where
every possible variety of this rock from Gribon to Ben More, and
thence to Loch Don on one hand, and Mornish on the other, ap-
pear to succeed each other without discontinuity or interruption,
and with changes of character so gradual, that no line of interrup-
tion can any where be found, As however I consider this to be an
object of the first importance in the history of this rock, I shall
still suspend my judgment, pointing it out to other geologists as a
subject highly worthy of investigation.

As I consider the term /Zcetz to be in this case improper, since it
implies the hypothesis from which it is borrowed, I have distinguished
that trap which is placed in a horizontal form, and of which the
terraced edges are so very characteristic, by the name of stratified
trap, using the term beds or strata indifferently, and without
meaning by the use of either to insinuate any thingres pecting

56 Dr. Mac Cutiocn’s Sketch of the

the mode of its formation. The other I have called mountain
trap.

The terraced trap forms by far the greater portion of the surface
of Sky ; but as it is sufficiently defined in the map and in the ge-
neral description, I will forbear here to name its boundaries. Its
northern and principal tract is every where continuous, but at the
southern side of the island there are detached portions, which I
shall first notice. The southernmost in position is a hill of no
great extent, which is seen above the secondary strata already de-
scribed at Swenish point, between Loch Slapin and Eishort. This
mass is connected with two large bodies like roots, (inasmuch as
they have neither the parallelism nor the independence of trap
veins) which cut through the whole mass of strata, and disappear
below the sea. I consider this place as of great importance in the
history of trap, as it shows plainly how a particular mass of that
rock may appear fairly incumbent on a given stratum, while it is in
fact connected with a much deeper set of rocks.

It is plain that partial views of this mass at any one point of all
the various substances which it traverses, would assign to the same
rock all the several hypothetical characters according to which trap
has sometimes been divided. It would be called in one place primi-
tive, in another transition, in athird fleetz, and so forth. AsIdo
not intend to enter into the well-known questions respecting the
origin of trap, I forbear to point out how this appearance bears
on any of the hypotheses which regard its formation.

The next of the stratified masses of trap which are seen toward
the south are the hills which decline from Blaven to Strathaird, and
appear to be similarly incumbent on the stratified rocks of that
promontory, but I had no success in my attempts to discover their

Mineralogy of Sky. 57

junctions. These are the only detached masses, the remainder of
the stratified trap forming one continuous mass, occupying the
limits already referred to. It would be an endless toil to follow
the varieties of this rock in the narrative as I did in the examina-
tion, as fatiguing to the reader as the writer, and equally useless
either in a topographical or geological view. After describing such
‘of its connections with the secondary strata as can be discovered,
I shall content myself with enumerating a few of the most leading
varieties, particularly such as add any illustration to the history of the
rock, and with describing the localities of the most remarkable strata.

The contact of the stratified trap with the secondary rocks
is seen very frequently on the eastern coast, as well as on the
western shore of Loch Snizort, but it never occurs between Dun-
vegan head and Soa. In speaking of the secondary strata, I have
already mentioned the most remarkable points where these contacts
are visible, and need not therefore repeat them: they are most ac-
cessible in the neighbourhood of Duntulm, and from Portree north-
wards the alternations can be readily traced. I observed nothing so
particular at the junctions in any place as to require a detailed de-
scription, except the contact of the basalt at Duntulm Castle, with
the siliceous schistus, which I shall describe hereafter.

Among the numerous species of the trap family here existing,
basalt is the most conspicuous, and it occurs almost every where,
alternating in an irregular manner with all the other species-or va~
rieties. It is most frequently amorphous, displaying at the same
time so great a variety both in its natural mode of breaking, in its
external appearance on weathering, and in its texture and colour, as
to form a great number of subordinate varieties much more re-
markable in their natural situations than when broken into hand
specimens, At Talisker it is found perfectly black, and of an ex~

VoL. II. H

58 Dr. Mac Cuttocn’s Sketch of the

quisitely fine grain, as also in other situations both on the western
and eastern shores. Considering the great extent of this rock it is but
rarely columnar. The most beautiful and conspicuous collection of
this nature is found at Little Brichel near Talisker, and ranges of
tolerably defined pillars are also to be seen in many places of this
neighbourhood occupying elevated situations in the cliffs. Columns
of considerable regularity are also found at Floddigary near the
north end of the island, and immense and continuous ranges of a
kind imperfectly defined occur in the vicinity of Duntulm.

The next of the most conspicuous varieties of trap in Sky is
amygdaloidal. Ishould perhaps in strictness rather have defined this
rock by its base than by its structure or accidents, but mineralogical
language has no means of distinguishing, not only the infinite va-
riety, but the perpetual variation of the bases which are seen charged
with these nodules of occasional minerals. It is sufficient to say,
that in hardness the base varies from basalt to almost the softness of
dry clay, and that the colours are black, bluish, brown, dark purple,
and gray of different tints, sometimes of a very pale tone. As
these varieties often occupy different strata, and are variously inter-
mixed with the solid kinds already described, the strata, when viewed
in the cliffs, often seem to possess a variety of composition which
when examined into proves fallacious. The nodules imbedded in
these amygdaloids are very various, few of all the substances usually
met with in the trap rocks being wanting in some part or other of
Sky. The zeolites are the most conspicuous, since all the varieties
but one, the ichthyopthalmite, is found occupying their cavities, and
often in forms so large as to require a separate consideration in the
subsequent part of this paper.

Calcareous spar, chlorite, steatite, quartz, chert, chalcedony, and
prehnite, occur in other varieties ; among which the two latter are

. Mineralogy of Sky. 59

most rare, and on no occasion have I seen barytes, a substance not
uncommon in the trap amygdaloids of other places. At Talisker, mica
is to be observed in some varieties, a substance among the least
common; and in the vicinity of Scavig, epidote is an ingredient,
the rock resembling precisely the specimens found in Caer Caradoc.
I have never met with olivin in these traps.

Various complexions of greenstone are found among the strata in
different parts of the island ; but they are far less common than the
basaltic varieties. In one instance I observed specimens in which the
crystallization of the hornblende was very perfect. The porphyries
of this kind occur also in different places, but like the greenstones
they are much inferior in quantity to the uniformly basaltic kinds.
The felspar is sometimes glassy, sometimes opake, and the com-
pound at times forms beautiful specimens. I did not observe among
the stratified trap any example of clinkstone ; and wacke is I believe
totally unknown in this island, although some of the more earthy
amygdaloids have been improperly designated by this term.

The substance known by the name of trap tuff, and which I have
for reasons elsewhere assigned called trap conglomerate, is the last
which I shall enumerate of the varieties which come under the ge-
neral denomination of trap, and indeed no more can be enumerated,
since the terms applied to the several members of this family are
exhausted. This also occurs every where, and (as is I believe very
common) every where irregularly intermixed with the other va-
rieties. I saw no example however of that variety containing
rounded nodules and foreign substances which occurs in Canna, the
conglomerate in Sky always appearing to form a loose mass of angu-
lar fragments of gravel and sand easily mouldering to dust and soil.

It is now necessary to describe some substances which although
not appertaining to this family are often found united with it, and

H 2

60 Dr. Mac Cuttocn’s Sketch of the

some of them rarely, if ever, any where else. They were too small
in quantity, and too little connected to admit of a place among the
stratified rocks. ‘These are iron-clay, coal, siliceous schist, and a
particular sort of jasper. They occur separately or together in dif-
ferent places, but the whole are very conspicuous at Talisker. They
are all extremely irregular in their positions, and discontinuous in
their lateral extent. The iron clay is the most abundant of these,
and forms considerable beds in the cliffs about Talisker, and along that
coast as far as Loch Brittle. It is of various colours, red, purple, blue,
and gray, and these are often very lively, giving to the cliffs the ap-
pearance of having undergone the process of calcination. The coal
is rare, but occurs in different places, and its character in such situ-
ations is so well known that it is unnecessary to describe it. The
siliceous schist is not abundant, but it is found in ‘its most ordinary
form, and also in that very remarkable concretionary globular shape,
which having described at full length in speaking of the Shiant
Islands I need not repeat here. The jasper is rare. I have used
this term because I know of no other by which it can so well be
characterized. It is yellow or brown, with a lustre approaching to
resinous, and is well known as a product of the volcanic island
St. Helena. The specimens of Sky differ in no respect from those
of this island, which have sometimes, but improperly, been called
pitch stones. That they are not such, if proof were necessary,
would be sufficiently proved here by the regular gradation which
they undergo into clay, appearing indeed to be portions of clay
which have undergone changes in consequence of their vicinity to
the basalt, resembling the well known ones which sandstones expe-
rience in similar situations*. The succession of these several sub-

* T have since received similar specimens from Guadaloupe, where they occur among the
lavas of that island, adding one more to the numerous analogies already existing between
the voleanic rocks and the trap family.

_

Mineralogy of Sky. | 61

stances is often found in the same place, but their order can never
be ascertained, for, the cliffs rising toa height of 500 feet or more,
they are so far out of reach as to prevent us from forming an accurate
judgment respecting the individual parts. It is only by examining
the fallen specimens that we can ascertain the number of the varie-
ties in any spot. ‘They seem to me greater from Loch Bracadale
to Loch Brittle than elsewhere, but possibly this opinion may only
have arisen from the greater facility which I experienced in examin-
ing this line of the coast. I have in several places attempted to count
the number of strata, and they seem to vary from eight or nine to
twelve, fifteen, or even more, but it is not easy to define their
boundaries at the distance from which they must be viewed. The
way in which the several beds decompose often adds a very remark-
able feature to the cliffs: some become scoriform, others moulder
into large cavernous shapes, while a third set fall to powder; and
these various appearances, combined with the colours of the iron clay,
give to the whole that aspect of having undergone the action of fire,
which strikes a common observer even more forcibly than a geolo-
logical one.

I must now proceed to describe the trap which forms the moun-
tains, and which is not entirely limited to the Cuchullin hills, since
it is found constituting a great portion of Blaven, as well as parts
of the hill of Glamich, and of others whose names cannot be ascer-
tained, but of which the predominant parts are syenite and clink-
stone. I have no means of defining their limits with greater accu-
racy, partly because there is no sufficient map, and partly because the
country is nearly impassable in many places, and in others quite
inaccessible.

I have attempted to trace at the foot of Garsven, the southern-
most of the Cuchullin, the point where the stratified trap ceases and

62 Dr. Mac Currocn’s Sketch of the

the mountain trap commences, because there only are they seen on
the shore. Hitherto I have had no success, although there is a de-
cided difference between the disposition.of the two if distant points
are assumed. I should have been convinced that such a distinction
was to be found though I had failed in finding it, had I not been
equally unsuccessful in determining the transition of the two in
Mull. Yet I am still inclined to suspect the accuracy of my own
observations, and I must leave it therefore as a point to be ascertained
by those who shall think fit to follow me.

The junction of the mountain trap. with the stratified rocks is very
visible for a considerable space. between Soa and Loch Scavig. It is
here found in contact with the red sandstone, which I have fully des-
cribed in its proper place. No appearance of the upper strata is here
to be seen, the whole body of the mountain following upwards im-
mediately after the sandstone. 1 know not that any thing worthy of
notice exists at the junction. All the strata, both of schist and sand-
stone, are here as equal and straight as elsewhere, or if they are dis-
turbed it is by the trap veins which are independent of the moun-
tain. Nor are these rocks marked by any particular induration or
affection of their composition. Yet I may remark that their angular
élevation is less regular than at Loch Eishort, and that they are fre-
quently inclined at much higher angles with. the horizon than in this
latter place. 7

It will be readily apprehended from the remarks which have been
made in the geographical description of Sky, that the peculiarities in
the outlines and appearance of the mountains arise from the mode in
which the rocks that constitute them: are disposed, and from the
forms which these assume during the progress of disintegration. In
describing the forms of these rocks I can only pretend to detail the

Mineralogy of Sky. | 63

characters of the southern part of the group, Garsven and Blaven,
since I was unable to procure access to the other portions of it,

In other parts of Sky we have seen that the greenstones as well
as the other varieties of trap, are disposed in a flat or apparently
stratified manner by which the general aspect and outline of all these
portions of the island are determined. Tere on the contrary the
external outline and general features are those of granite, and I may
say that to its forms they appear also to add its permanence and du-
rability. They are disposed in huge curved beds of which the
external angles are, like those of granite in similar cases, slightly
rounded, and they extend over considerable spaces, offering smooth
sheets of rock unmarked by a single fissure or indication of past or
future fractures. No eye could distinguish them from granite except
by examining their composition. Their resemblance to this rock in
disposition, and their dissimilarity to the greenstones of the stratified
parts of the island, are in every way so decided that no position can
be assumed, nor any view taken of them, however general, or on a
scale however comprehensive, which can convey the slightest idea
of a tendency to stratification. Nor do they in any case that I have
seen shew the tendency to vertical fracture so common among green-
stones, being in every respect, except that of mineral structure, en-
tirely different from the ordinary varieties of this substance. Their
granitic aspect is still further expressed in a most striking manner
by the spiry forms of the summits, by their hard serrated outline
and their overhanging masses, a disposition by which they are ren-
dered inaccessible even to the stags and the wild goats that roam
over this region of solitude and rocks. To this is owing their highly
picturesque aspect, which bears a striking resemblance to that of the
granite hills of Arran, or the more stupendous masses of the granitic

64 Dr. Mac Cuntocn’s Sketch of the

Alps. It offers one instance among a thousand others of the little
dependence to be placed on the characters of the outline in deter-
mining the nature of mountains, and shows how easily geologists,
who have assumed the certainty of such a criterion and used it in.
their investigations, have been ledto deceive themselves, and have
contributed to the deception of their readers. But I must proceed
to particulars. 4

Many varieties of rock are found in these mountains, of which
some appertain to the trap family more strictly speaking, and others
to the clinkstones, a set of rocks which, although they are inti-
mately associated with these, possess also some other natural afhi-
nities, which may render it more convenient to consider them as
members of another division. ‘The phenomena to be observed in
Sky are however insufficient to illustrate the views on which I am
inclined to allot a place for these rocks in the system, for which
reason I shall reserve these remarks till another occasion, when
more numerous and more explicit facts will enable me to make
the evidence proceed hand in hand with the theoretic arrangements
to be established on them. I shall therefore content myself with
describing the several rocks in a general way, since an attempt to in-
vestigate their connections more accurately, would involve too large
and unjustifiable a portion of conjecture.

Greenstone appears to be the most prevalent of the rocks which
form this group, and it varies very much in its character in different
places. It is often of the most ordinary aspect, consisting of the
usual admixtures of hornblende and felspar, and not at all distin-
guishable from those which appertain to the stratified parts of the
island. This modification passes as usual into one in which the
constituent parts, from their minuteness and intimacy of mixture,

Mineralogy of Sky. 65

cannot be distinguished, and which ought therefore to be con-
sidered a basalt, since no other criterion can be established between
the two, the variable proportions of hornblende and felspar alone
admitting of no better or more defined limit than this. More
generally in these mountains the greenstone assumes a large grain
and very coarse texture, and in some cases the separate substances
exhibit crystals of a quarter of an inch in dimension, while the
hollows which are found in the rocks are sometimes occupied by
detached crystals of hornblende. The felspar in these examples
is often of a greenish hue. This rock appears remarkably perma-
nent, showing few traces of waste or decomposition of the surface,
and it is of this particular variety that the rugged summit of Gars-
ven is composed. Among the finer grained varieties a remark-
able kind is found on the borders of the romantic lake Cor-
uisk, where it lies in detached blocks rolled down from the sur-
rounding mountains. It is honey-combed into large cavities, which
allow the hand to enter deeply within them, while at the same time
the surfaces are almost as fresh as if recently broken, showing none
of that rusty stain which attends the decomposition of greenstones
in general. These blocks are extremely sonorous, and, notwith-
standing their thickness, they ring when struck, with a sound as
gteat as, and precisely similar to, that of a thin vessel of cast iron.
In other places the same rock is found studded over with large de-
tached protuberances resembling pedunculated fungi, or huge nails
driven into it. The last variety which I shall mention is found
in the same place, and it-is the most remarkable, since it presents
a modification of trap hitherto undescribed. It forms a great por-
tion of that naked and wild surface which I have already described
in the general account of this spot, being disposed in enormous
smooth inclined beds extending, without-fissure or trace of decom-

WOr.! 117. I

66 Dr. Mac Cuttocn’s Sketch of the

position or fragment and without symptom of vegetable life, from
the borders of the lake to the summits of the mountains. Of its
interior extent I have no means of judging, since it is inaccessible.
This rock is composed fundamentally of felspar and hornblende; -
the parts being always distinct and crystallized in various sizes, so
as to form varieties more or less coarse. The felspar predominates
in the compound, and is either glassy or inclining to that variety ;
at times indeed quite opake. ‘To these is superadded hypersthene,
but it is neither so abundant as the hornblende, nor is it found so
generally dispersed through the rocks. — It is traversed by veins of
basalt, and by veins containing hypersthené in a larger and more
distinct form.

The other rocks which are found in the Cuchullin hills may alt
be comprehended under the general term of clinkstone. I find it
impossible even to conjecture the relative spaces which are occu-
pied by the rocks of this division and the greenstones, but I have
already said that the greenstones appeared to me most prevalent.
In the southern parts of the Cuchullin they undoubtedly are so,
but I am inclined to think that in Blaven, and in those hills which
contain the light coloured syenite mixed with darker coloured rocks
and which are as I have already noticed so easily distinguished at a
distance, the dark rocks will be chiefly found to consist of clink-
stone. ‘The varieties which occur are as numerous as they usually
are in the different situations in the western islands where this
rock is found, with the single exception of Arran, which presents
an infinite and instructive variety of them in all their modifications
and transitions. In general the clinkstone is simple in its compo-
sition, and of a dark lead blue, which sometimes assumes a brighter
hue, and occasionally passes through various tints to a pale whitish
gray or ash-colour. In many places it is porphyritic, the porphy-

Mineralogy of Sky. 67

ries putting on a great variety of aspects varying with the colour
of the base, the quality of the felspar which forms the crystals,
their magnitude, and the density of their aggregation. Blaven
offers a remarkable variety, in which solitary crystals of glassy fels-
par nearly two inches in length are sparingly disseminated through
the ground. The beautiful variety consisting of pure white crystals
fin a ground of dark blue, which is found in Raasa, also occurs in
Glamich. But it would be fruitless to describe these varieties.
In the same hill it is found of an amygdaloidal texture, but, as far
as I have examined, the cavities contain only crystallizations of
epidote similar to those occuring in the greenstone which I have
already mentioned.

Such are the rocks which as far as my observations extended
form that mass, which, for want of a better general term, I have de-
signated by the name of mountain trap. It is however evident that
the rugged aspect and permanency of these hills cannot in any de-
gree be attributed to the clinkstone which enters into their compo-
sition. We have examples sufficient in Mull and in Arran to show
that hills of clinkstone always form in the progress of their decom-
position a feeble and smooth outline. The same indeed occurs in
these very hills, since the outline of Glamich, and of the other
-mixed hills in which clinkstone forms the dark part, is equally tame
and rounded. From this knowledge we are led still more strongly
to conclude that the hard and serrated summits, and even the main
body of the hills which present them, are composed of some of the
varieties of greenstone before described, and hence to conjecture
that this substance forms their principal ingredient, and that the
clinkstone is only found on those outskirts where the passage or
change into syenite takes place. We have I fear no means even of
conjecturing the causes of the difference either in the disposition or

12

ed

68 Dr. Mac Currocn’s Sketch of the

in the durability of these mountain greenstones and those of the
stratified trap, or of forming any probable conclusion respecting their
eras of formation. Much remains to be learnt before we can attain
to an accurate knowledge of these rocks, and there is much yet re-
maining for future observers in the ground which I have now trod-
den. But it is not an easy task to ascend these pinnacles and to
traverse this rocky desart even in summer, and summer seems
never to shine on them—at least it has never yet shone for me.

I must now proceed to consider the last rock which remains un-
described, the Syenite.

In describing the Cuchullin, I have for the sake of contrast in-
troduced so many of the most remarkable features of the other
group, which I have distinguished by the name of the Red Hills,
that the less will remain to be said respecting them. They are in-
variably characterized by the lumpish roundness of their outline.
The cause of this consists evidently in their rapid decomposition,
and in the accumulations of fragments which cover not only their
sides but their summits so completely, as to preclude in most places
any view of the naked rock. Their elevation I have formerly ob-
served is much less than that of the Cuchullin, and I have also
remarked that they form a separate assemblage, interfering at their .
bases only by indentation or approximation, and being always dis-
tinguished from the latter both in character and composition. The
summits most convenient of access are those of Ben-na-Caillich near
Broadford, with its dependencies, and the somewhat insulated moun-
tain of Glamich above Sconser, the highest of the group. As Ben-
na-Caillich presents the greatest simplicity of composition, I will
describe it first. It forms part of a group which descends into the
plain by various acute ridges, reaching into Strathmore and the head
of Loch Slapin on the southern side, and extending towards Scalpa.

Mineralogy of Sky. 69

on the northern. It offers no remarkable variety of composition,
but appears to consist of various modifications of that syenite about -
to be described, to which on a former occasion I proposed that the
name should be limited, the syenite connected with the trap for-
mation. ‘Those who are acquainted with the syenite of Arran, of
which the main constituent is felspar, will recognize in this a similar
rock, of which examples may also be found in the neighbouring
island of Raasa, as well as in many other of the Western islands.
The hill of Glamich may be selected as aspecimen of those which are
formed of syenite and of clinkstone, both of which are in this case
strongly marked, since, as already mentioned, the former displays its
reddish yellow hue, and the latter a dark blue tint. In other respects
there is no difference between these rocks in the general disposition,

which is in both equally irregular and ill defined. I could not dis-
cover the contact of these substances, but am convinced from other

observations that they are connected by a common bond of tran-
sition or of position, and that they present no essential differences
in geological relations. As the syenite of this hill presents no
peculiar varieties, and as the clinkstone has been already described,
one common description of the former will serve for the whole
group. There is probably cause for me to regret that I could
procure no more extensive access to the hills of this group,
but the uninhabited and desart state of this tract of country renders
it nearly impossible, since the limits of the longest day are insuffi-
cient for their examination, and since the storms and rains of
this wild island form but a dreary canopy to its rocky pillow.
I can therefore add nothing more precise to the general idea I
have already given of the connection of the syenite with the trap
and with the clinkstone. The light coloured rocks which belong
to the group appear in all cases to consist of the several vari-

70 Dr. Mac Cuttocn’s Sketch of the

eties of syenite which will be described hereafter, while the dark
ones, with the exception of some greenstone, seem to be every
where formed of clinkstone. The tendency of these syenitic
substances to decomposition, explains the weathered appearance
of the mountains which I have characterized by the name of
the Red Hills, and the accumulation of the fragments which
result from it, accounts for the roundness and tameness of their
outline. ‘These causes very generally impede the view of the
natural rock. Wherever it can be seen it appears to possess the
disposition which is I believe invariably characteristic of this class of
rocks, forming large irregular beds, much rifted and fissured, and
never continuous in inclination and extent for any considerable space.

It might be deemed important to determine here the nature of
the junction between the dark clinkstone and the light coloured
syenite, but if it has not been discovered here, it is fortunately visible
in other places, while at the same time the community of these two
rocks, in almost every circumstance but colour, seems to bespeak a
common position. Ben-y-chat in Mull, and many situations in
Arran, present examples of this connection, nay in some cases of a
perfect transition. The phenomena visible in Rum, in St. Kilda,
and in others of the Western islands conincide with these, and
offer a proof which may by a fair analogy be extended to Sky,
that there is a community of geological position in these two
rocks.

I have much more reason to regret the insuperable difficulties
which I experienced in attempting to trace the connection between
the syenite and the stratified rocks, the sandstones and limestones
which were described in the commencement of this paper.

The only real contact of this substance with those strata is to be

seen at the marble limestone in Strath, and I have traced it in the

Mineralogy of Sky. 71

excavations made for quarrying that marble. I have always found
the marble much indurated and very much coloured at the contact, be~
ing at the same time contaminated with silica and other earths; while
the syenite itself in the same places appears rotten. Although ina
general sense the contact of these two rocks may be said to be visible
‘in various parts of this tract, some accident or other always occurs
at the point of meeting, to prevent the real contact from being seen.
If it is of small extent it is overgrown with soil and herbage ; if. it is
of great dimensions, there is a chasm intervening which is filled with
fragments and rubbish. ‘Thus the contact at Kilbride, which would
otherwise prove instructive, is overwhelmed and invisible. I was
“equally unable to find any place on the eastern side where its junction
with the upper of the secondary strata could be-observed, though it
unquestionably takes place near Broadford ; the soil is every where
a deep peat completely covering the rocky surface. It may pro-
‘bably be found on the shores between Broadford and Scalpa. I
know not that there is much to regret in not having seen more of
its connections with these strata, since, if, as I believe is undoubted,
it has the same relation to them as the trap has, no instruction fur-
ther than that which we already have can be derived from such
knowledge. It will be found indifferently interfering with every
one of the strata, and consequently no judgment of priority or pos-
teriority to any can be formed respecting it.

The basis of the syenite is a substance which having been gene-
rally received as a felspar, I shall describe as such, although not con-
vinced of a sufficient identity in the composition of these two sub-
stances. In its softest state it may be considered as a claystone,

since it offers no differences in character, while in a state of some-
what greater induration it becomes a clinkstone, and when more

72 Dr. MAc Cutiocn’s Sketch of the

hardened it is known by the name of compact felspar. As specimens
occur in this simple state they must be considered mineralogically as
examples of these different substances, although in a geological sense
we cannot without troublesome circumlocution and great confusion
consider them under any but the general term already adopted. The
colour of this base varies from ochrey yellow and dirty flesh colour
to gray: it is often cavernous and filled with a ferruginous clay. In
other situations it contains crystals of felspar, either of the same or
of a different colour, and thus forms various kinds of porphyry.
The predominant form however is that whence its name has been
imposed, an aggregate of felspar and hornblende, in which the
hornblende generally bears a very small proportion to the other
ingredient: the porphyritic character is sometimes added to this
mixture. In some rare instances quartz enters into its composition,
and in such instances it trenches near upon the syenitic granite, a
distinction concerning which I have spoken in the paper on Glen
Tilt, to be found in this volume. More rarely still it contains mica,
and in this case it becomes utterly impossible to distinguish it from
those granites which contain crystals of hornblende superadded to
the usual threefold mixture of quartz, felspar and mica. Under
such circumstances it is quite conceivable that specimens should be
met with from which the hornblende was absent, since even in
those I have described, it is very thinly scattered through the mass.
In such a case, should it occur, mineralogy, unassisted by geological
observation, would tend to mislead us in reasoning respecting its
position, and we are thus driven to acknowledge, in geological
description, the necessity of superadding to mineral characters an
accurate knowledge of the connections “of a:rock respecting which
we are reasoning: I must therefore, from a geological knowledge of

Mineralogy of Sky. 73

the position of these rocks, refer them to the syenite family, although
had I met with the same specimens connected with a mountain of
granite, and lying under mica slate, I should have referred them to
the granites.

This is far from being the only case in nature where mere
mineral distinctions are insufficient to determine the geological
situation of a rock. In the stratified classes of rocks, both primary
and secondary, these resemblances are frequent, since it is often
impossible to distinguish quartz rock from sandstone, the breccias
which it contains from the more recent graywacké, ancient clay
slate from recent, or, as I have shown in this very account of
Sky, primitive from secondary limestones. The same rocks seem
in some cases to have been repeated at different epochas, while in
others they show variations which may perhaps be the results
of posterior changes operating on the first deposits rather than
the consequences of original differences.

Two other varieties of this rock occurred to me which may be
mentioned, although possessing no peculiar interest. In the one
chlorite formed a constituent part, and in the other a greenish com-
pact steatite was intermixed with the felspar and hornblende, the
total compound being not much unlike the porcelain granite of
Cornwall.

Before I conclude these remarks on the trap and syenitic rocks of
Sky, it will not be superfluous to enumerate the striking external
features in which rocks so nearly associated differ.

The mountain trap of the Cuchullin is most strongly distinguished
from the stratified in the difference of its disposition, in the absence
of the columnar forms and decomposing tendency, and in the bar-
renness of its surface compared with the deep soil and highly clothed
vegetable surface of the latter. In its superior permanence, a per-

VOL. IIl. K

74 Dr. Mac Cuttocn’s Sketch of the

manence by which it appears to brave the external war of the ele-
ments which surround it, it is no less distinguished from the
stratified trap than it is from the neighbouring Red mountains,
whose rapidly decomposing summits covered with fragments have
long lost their characteristic forms, hastening with daily and visible
waste to the level of the plain below. It is equally distinguished
by its general aspect, being commonly separated by marked features
from the terraced trap with which it is associated, and no less so from
the Red hills, with which, however associated in almost a common
group, it forms no union. In mineral composition it also differs
widely from these, hornblende forming its predominant and charac-
teristic ingredient, as felspar does that of the latter. From the
terraced trap it differs less in composition, since hornblende is the
predominant ingredient of both, but it never like this contains amyg-
daloids and beds of tufo, neither does it entangle coal, sandstone or
ironstone, or exhibit the beautiful zeolites so abundant in the
terraced trap.

If there were any theory of the formation of the rocks of this
class on which we could rely, it would not be useless to examine
how far their distinctness of character and appearance was consonant
to it, or how far they differed. Although my chief object has been to
describe the geological features of the island, yet I may suggest that
such an independence of character and: form seems to imply at least
that some independence in circumstances, as well as in time, has
accompanied the formation of these several portions of a rock
associated in so many other essential parts of their leading characters.
But the time for discussing questions-of this nature does not appear
yet to have arrived, and conjectures may be left to the ingenuity of
those to whom they afford a source of gratification.

_ With this rock I terminate the history of the principal rocks
of Sky.

Mineralogy of Sky. 75

“When speaking of the alluvial rocks, I did not mention granite,
as I did not find any rolled stones of this substance. But as I ob-
served it employed in the construction of a bridge not far from
Sconser, I conclude that it is somewhere to be found and probably
in this state, as I saw no reason to suspect its existence any where,
as a fixed rock.

I have reserved to the last the consideration of the trap veins
which are found in such abundance throughout the whole of this
island, because, on account of their number and the interesting cir-
cumstances which attend them, they would have led to a perpetual
interruption of that description which required to be unbroken.
I have here, as on other occasions, applied to these veins the general
term trap, for the same reasons which I assigned in speaking of the
rocks of this class, namely, that they vary in composition, although
basalt is certainly the prevalent substance in them here and every where
else. ‘The order which [ have allotted for them in this description
is also the order which they hold in nature, since they traverse
every rock that lies in their way from the most ancient to the most
recent, seldom suffering any change either of direction or com-
position in this varying course. As the same vein is therefore found
to pass indiscriminately through rocks of all ages, it is plain that its
association with these can afford no register of the period of its
formation. If there were ten different periods in which these veins
had been formed, we must be contented in most cases to prove but
one, a period posterior to that of the latest stratified substance through
which they pass. It is only where they interfere with each other
that a register more extensive than this can be found. I have
always assiduously sought for such examples wherever these veins
abound, and, among other places, in Sky, but have never yet found

more than two distinct sets. ‘This number I have also observed in
ae ;

76 Dr. Mac Curtocn’s Sketch of the

Rum. Two distinct sets are perfectly visible both near Loch Scavig
and at Strathaird, and the examples are unquestionable, since those
of one period hold their course through the other in every direction,
with the same pertinacity and distinctness as the first do through
the fundamental rocks. We have no means of knowing what dis-
tance of time has intervened between these veins. The angle of
their courses with the horizon is various, but in a very considerable
proportion it is vertical or nearly so.

They are of frequent occurrence in the mica slate of the district
of Sleat, and, as far as I have seen them, they are here basaltic,
They also abound in the sandstone at Loch Eishort, where they are
of considerable size. From this bed they are readily traced through
the superincumbent ones as far as the most distant surface of the
_limestone, and here I have always lost them. In several attempts
for that purpose, I never could discover their continuation through
the syenite, and am therefore inclined to think that they are prior
to it. To ascertain this fact, I caused a portion of the marble bed
which was traversed by two of these veins to be cleared away to
its contact with the syenite, and found that the whole mass termi-
nated together against it, leaving in my mind little doubt that the
syenite was posterior to the veins. This fact has a double bearing:
it might be argued that the stratified rocks reposed on the syenite,
since the nature of the contact between stratified and unstratified
rocks is always such as to admit of a double interpretation, unless
where veins of the one are seen decidedly ramifying from its mass
into the other. But if, as in this instance, the trap vein, which we
know to hold in all cases an unchecked progress through opposing
rocks, is cut off by the unstratified rock, the syenite, it is plain that
the stratified rock which that vein traverses has also been broken
by it, and that the syenite in this particular case is posterior to the
limestone, and of course to all that body of rock which precedes it.

Mineralogy of Sky. 17

It follows then that the syenite is posterior to the trap veins, and a
further confirmation of this is found near Scavig, where a set of trap
veins is also to be seen which traverses the red sandstone, but does not
pass through the incumbent trap; therefore the syenite, and the moun-
tain trap of the Cuchullin, are each posterior to one set of trap veins.
This adds a probability to my conjecture, that the mountain trap and
the syenite are of one period ; it cannot be said to prove it because we
have no means of knowing whether or not these separate sets of veins
belong to one period or to more. Community of structure proves
nothing in this case ; they are equally formed either of a coarse basal-
tic substance, which can scarcely in strictness be called basalt, or of
porphyritic trap ; and would be with still less propriety denominated
greenstone, since the two substances, whose distinct union forms this
latter rock, and whose imperceptible mixture is supposed to form the
other, cannot be traced in it.

But I must not terminate the history of these veins which appear
in such a profusion of intersections in the vicinity of Scavig, without
remarking that however numerous they may be, and consequently
however large the space which they occupy, they produce little or
no disturbance in the regularity of the sandstone beds which they
traverse, nor does that rock appear to undergo any alteration in
their vicinity. This remark will appear the more necessary hereafter,
when I shall describe a similar but infinitely more striking pheno-
menon at Strathaird.

There is a second set of veins however, which traverse not only
the mountain trap but the veins first named, and which are clearly
of a posterior date. These are much smaller, often indeed not ex-
ceeding half an inch in breadth, and are composed of an extremely
fine and hard black basalt. They are less abundant than the first
where even they exist, and they are not found in nearly so many

78 Dr. Mac Curtocn’s Sketch of the

situations. They are to be observed pretty frequently passing through
the rock at Coruisk, and through the greenstone and clinkstone of
Garsven, in the neighbourhood of which latter they abound. Their
compactness and lustre are frequently so great that they approach in
appearance to that pitchstone which forms the basis of the beautiful
columnar porphyry of Egg. In addition to this feature they are
strongly distinguished from the trap veins that traverse the sand-
stone by the intimate and almost inseparable union which they form
with the body of the rocks which they traverse, whereas the latter
are separated with the greatest ease.

There is still another set of veins found in this place, which how-
ever even and compact they may appear on a fresh fracture, and thus
resembling basalt, appear to consist of clinkstone. This may be con-
cluded from the facility with which they decompose at the surface
into a greyish or whitish earthy looking substance, and from the
depth of that decomposition. They are further distinguished by the
frequency and minuteness of their ramifications, which are often
drawn out to the size of a thread. Veins of this description have not
as far as I know, been noticed, but they are not uncommon in the
western islands, and they abound particularly in some parts of the
Long isle; in this place they are chiefly seen on the borders of
the small and picturesque lake Coruisk, and are found traversing the
hypersthene rock, as well as the veins themselves, which consist of
this mineral.

Having now described the trap veins which pass through the
mountain trap, and those, perhaps more important ones as far as re-
lates to that rock, which do not pass through it, I must turn the
reader’s attention to those which are found in the stratified trap.
These are not very abundant, but may be seen distinctly among
ether places on the western shore, traversing the lofty. cliffs in various.

Mineralogy of Sky. 19

but generally perpendicular directions. They are of a very large
‘size, and are frequently stratified, a circumstance not uncommon in
basaltic veins. They do not resemble the small ones of the second
rank which I have described already.

If, as some have seemed inclined to do, we should adopt a
notion that all trap veins were of the same period, the existence
of these in the stratified trap, while they were absent from the
mountain trap, would lead us to conclude that this latter was
a posterior formation to the other. This is possible, and I
have certainly no proof to the contrary. But from what I have
shown respecting the certainty of two distinct sets of these veins, and
the possibility of more, it is plain that they can prove nothing re-
specting either the difference or identity of these two rocks. If there
are two sets of veins there may be three or more,

As no useful purpose is served by describing all the trap veins which
abound in these countries, I shall pass over many which offer no inter-
esting features in themselves, and are of no evidence in geological in-
duction, and finish by describing those that are to be seen at Stra-
thaird, which are well worthy of notice on account of their extraor-
dinary number, and of some particular appearances by which they
are distinguished. I have already slightly mentioned them in the
general description of this coast: I must now be more particular,
and, to give an idea of their general appearance, I have subjoined
what must rather be considered as a plan than a drawing, since the
formality of the subject admits of nothing else.* I pointed out their
extraordinary numbers, and may now add that in consequence of
their frequency they nearly equal in some places, when collectively
measured, the stratified rock through which they pass. I have
counted 6 or 8 in the space of 50 yards, of which the collective di-

* See Pl. 4. fig. 3.

80 Dr. Mac Currocn’s Sketch of the

mensions could not be less than 60 or 70 feet. This remark is not
mere matter of curiosity, it leads to geological inferences not un-
worthy of regard, as will be presently seen. Their direction is
almost invariably either vertical.or slightly inclined from the plumb,
and they present therefore a perpetual parallelism along the coast.
They are equal throughout, and never ramify, and although they
vary from 5 feet to 20 in breadth, they more commonly are of a
dimension not exceeding 10 feet. It is well known that the perma-
nence of trap veins is sometimes less, sometimes greater than that
of the surrounding rocks. Hence they sometimes project like walls,
while at others their ruin produces fissures or caves. This latter
effect has taken place here, marking a great tendency to decompo-
sition in these veins, since the including rocks do not seem to be of
a very durable nature. The depth to which they have been exca-
vated is often very considerable: in the case, of the spar cave inclu-
ding the external fissure, it cannot be less than 250 feet. In conse-
quence of this wasting it happens that the intermediate cliffs which
remain, have, asI have noticed in the general description, the ap-
pearance of the ends -of walls; and as they also sometimes yield and
fall away behind, in such cases they present the appearance of in-
sulated square pillars of masonry, the resemblance being rendered
perfect by the channelled marks of the strata formerly described.
These veins are often stratified, or more properly speaking, lami-
nated in the direction of their length. They are generally formed
of a bluish black basalt; at times they are porphyritic, or vary in
other ways, which it is unnecessary to describe. I observed in one
nodules of prehnite, the only occasion on which I have found that
mineral in veins of trap. In another I found a second vein, holding
a serpentine course through the first in a somewhat parallel direction,
and readily distinguished by being formed of a much more black

Mineralogy of Sky. $1

durable and compact basalt. I have given a sketch of it. (Pl. 2.
fig. 3.) I may finish the description by saying that the continua~’
tions of thece veins are to be seen between Swenish and Kilbride,
at least, veins similar in appearance and equally numerous, but
that there is no trace of them on the opposite shore of Sleat in the
places which their prolongations would cut: they are not therefore
extensive in their courses.

It has been so general an observation that the courses of trap veins
are attended with disturbances cf the accompanying strata, that it
seems almost to have passed into a rule among geologists.
The present instance is a most remarkable one to the contrary.
Although they are here so numerous, not the slightest disturbance
takes place in the evenness and the horizontality of the strata of
sandstone which they intersect. There is neither contortion, bend-
ing, fracture, or displacement, nor do they appear to have affected
the texture of the rock, since it is the same both at the place of con-

‘tact and at a distance from it. Of exceptions to general rules it is
rare to meet with any so pointed and so strong ; and though there
is no room for any long commentary on it, I cannot entirely quit
this very remarkable place without pointing out one extraordinary
effect which must have resulted from the intrusion of these veins.
If the laterat dimension of the collective veins is assumed at one
tenth of that of the stratified rock, (and I have reason to think this
estimate not excessive) it is plain that the stratified rock of Strathaird
must have undergone a lateral extension equal to that quantity ; a
motion so great that it is extremely difficult to reconcile it with the
present apparent repose and regularity of the whole.

Wore 11. L

82 Dr. Mac Cutiocn’s Sketch of the

I shall now proceed to describe the mineral substances which I
observed in Sky, having reserved these details for separate consi-
deration, lest they should interrupt the connection of the geological
remarks which form the preceding part of this paper. The most
numerous, and not the least interesting of these minerals, are those
of the zeolite family. They are to be seen in various parts of the
island, but are to be found in the greatest beauty and variety in the
cliffs of the western shore between Loch Bracadale and Loch Brittle.
Talisker, as it is the most accessible of these places, so it presents
the richest assortment to the collector of specimens. But in general
the mineralogist can have no access to any specimens but those
which fall from the cliffs, and have long been exposed to the vio-
lence of the sea and the injuries of the air. However splendid
therefore, they may once have been, they are not always to be
found ina state of good preservation. It is moreover often difficult
to gain access to them on any terms, particularly along the other
points of this wild shore, since it is so beset with rocks on which a
dangerous surf is almost always breaking, that it requires neither com-
mon good weather, nor common dexterity in the management of a
boat, to effect a landing and retreat without hazard.

Analcime is the most common of all these minerals on the shore
to which I have now alluded, and it is found in the greatest pro-
fusion at Talisker. It sometimes occupies cavities of considerable
size, in different varieties uf the trap, but seems to be by far the
most abundant in those earthy and little compact sorts, for which
there is no name in our catalogue of terms. In other cases it forms
flat druses of considerable extent, occupying the walls of fissures,
while in a third, a single crystal is sometimes seen in a cavity just
sufficient to contain it. Inthe greater number of instances the re-
maining part of such cavities is filled with the filamentous meso-

Mineralogy of Sky. 83

type hereafter to be described, and the crystals thus seem to be im-
bedded in a mass of cotton.

The size of the crystals varies from that of a pin’s head to the
diameter of half an inch ; but in general they present only one mo-
dification, the twenty-four sided crystal with trapezoidal faces, of
greater or less regularity. The only other form which I found was
the primitive, and of that 1 procured but two specimens, while a
ship might be loaded with the trapezoidal variety. The crystals de-
scribed are sometimes opake and white, at others they are mottled
with a mixture of opake and transparent parts, while in a third,
but less common case, they are transparent. In this latter case,
when minute, they sometimes transmit the black colour of the sub-
jacent basalt to which they adhere, so perfectly as to resemble a
velvety surface of black crystals. In similar circumstances, trans-
mitting the greyish or ochry colour of the substance to which they
are attached, they appear to possess a colour which a more narrow
inspection shows to be fallacious. A few specimens however occur
of a flesh red, a colour frequently found in almost all the minerals
of this family, and very predominant in the different zeolites which
occur at Glen Farg in Perthshire. I also found a solitary specimen
of a pale sea green colour, but did not observe that variety of a
pale bluish grey, which, in company with the flesh coloured and
yellow green, I have seen in the rocks at Larne in Ireland.

Chabasite is found in similar circumstances on the same shore,
but it is comparatively of very rare occurrence: it abounds however
in the rocks at the Storr, which for a considerable space consist of
an amygdaloid containing it accompanied by stilbite. It is here so
common, occupying cavities of greater or less magnitude, that a
fourth or fifth part of the total bulk of the rock is sometimes con-

stituted by the chabasite.
L2

$4 -Dr. Mac Cutzocn’s Sketch of the

As far as I have observed, the chabasite which I have described
is never, like the analcime, imbedded in the filamentous mesotype,
but is not unfrequently associated in the same cavity both with
stilbite and with analcime, nor is it unusual to find minute and well
formed crystals of this latter substance, imbedded in the crystal of
chabasite. In some cases perfect crystals of chabasite are lightly
sprinkled over the surface of crystals of stilbite, adhering so slightly
as to fall off on the slightest concussion : in other cases crystals of
this mineral, as well as of the analcime, are confusedly mixed with
rhomboids of carbonate of lime, hereafter to be described.

The primitive crystal of this mineral is by much the most com-
mon, its modifications being rare and offering but few varieties ; it
is very frequently twinned, the angles of the one crystal appearing
on the faces of the other, nor is it uncommon to meet with it in
triplets, or even in more complicated groups, displaying an irregu-
lar mixture of prominent angles. The most common modification
consists in the truncation of one angle; sometimes two neighbour-
ing angles are truncated, and occasionally this defect extends to
three, the truncations being often so deep as to remove a third part
of the rhomb. In other modifications a single angle and a single
edge are removed, or the truncations extend to two angles and two
edges; but I have not observed any specimens in which these de-
fects were extended to a greater number of edges. The edge is in
some cases replaced by two or by three planes, or even by a greater
number, so as to appear nearly rounded; and each face of the
rhomb is also frequently replaced by two planes meeting in an edge
diagonally extended and sometimes rising by successive stages of
planes parallel to the original face.

These crystals are sometimes opaque, more frequently transpa-
rent, but in by far the greater number of instances they acquire a

Mineralogy of Sky. | 85

fallacious aspect of opacity in consequence of innumerable minute
fractures by which they are pervaded throughout; they are most
commonly white, but the flesh coloured variety is also found: their
magnitude varies from the twentieth to that of three tenths of an
inch in breadth.

, Stilbite is perhaps the most abundant of these substances which
Sky produces, and it appears to be the most generally diffused
throughout the island; it occurs along the shore which I have de-
scribed, but in less quantity than in the northern district. It is
so common in some places in the parishes of Kilmuir and Snizort
that it is scarcely an exaggeration to say, that the roads are some-
times almost made of it. In some situations the decomposed trap
falling into a powdery soil, leaves large accumulations of it re-
sisting the action of weather long after the rock has mouldered away,
while in other. places it has been converted itself into a friable mass,
which, as I already remarked, has been mistaken for marle and
used as manure.

It presents scarcely any varieties of crystallization: the predo-
pminant, I might almost add the universal form, is that most com-
mon one consisting of very flat tetraedral prisms, terminating in
tetraedral pyramids,, of which the faces are placed on the edges of
the prism. These are aggregated in distinct fasciculi, parallel or
divergent, of which the groups sometimes affect the form of the
constituent crystals. In the neighbourhood of Loch Eynort I ob-
served some specimens of great beauty, consisting of large and
distinct square prisms terminated at each extremity by truncated
tetraedral pyramids arising from the edges, the crystals being trans-
parent and nearly an inch in length, adhering slightly by its side
to the quartz crystals of the chalcedonic nodule in which it was
formed,

86 Dr. Mac Cuttocn’s Sketch of the

In the same place I found nodules of great size, and of a variety
which is far from common, but which has I believe been found in
the Faroe islands. The nodules in question are either hollow or
solid, and sometimes reach the enormous dimension of four and
even five feet. The hollow ones are crystallized within in the fas-
ciculated forms already described. The peculiarity of this variety
consists in its extreme frangibility: the least effort is sufficient to
detach the ‘plates of which its structure is formed, and it therefore
falls to pieces in the very act of procuring it, unless great care is
taken; its fracture is fresh, and distinguished by an uncommon
degree of the pearly lustre which is so characteristic of this mineral.
So great is its frangibility, that the jarring of the hammer at one
end of a large nodule is often sufficient to destroy the whole ; and
it not unfrequently happens, that when a large piece is obtained
entire and has been laid down, although it appears uninjured and
resists a strong effort of the hands to break it, yet in a few minutes
it falls to pieces with a sort of violence not unlike that which is
known to happen in unannealed glass that has received an injury.
This variety is sometimes white, and much resembling spermaceti
in its wanslucency, but in the greater number of cases it is of a
delicate flesh colour.

The next of these minerals is mesotype, and it is found in three
states, a compact, a mealy, and a crystallized form. Of these the
compact varieties sometimes recede so far in character from the
mineral in its most acknowledged forms, that it is only by tracing
the gradation of the several varieties, that we are enabled to de-
termine the names of those which occupy the distant points of this
range. The opake whiteness, the toughness, and the radiated
disposition of those specimens which may be considered as forming
the first remove, serves to connect them with the best characterized

Mineralogy of Sky. 87

ones. By a series of gradations the radiated structure disappears,
while the mineral acquires additional toughness, verging in its.
aspect first to chalcedony, and lastly towards chert; while in some
cases it would be difficult to distinguish it, without trial of its
hardness, from the white limestone of the north of Ireland: in
this state it is not scratched by hard steel, while its toughness is
such that a heavy hammer makes no more impression on it than it
would on a similar mass of iron. ‘The last transition is into a per-
fect chert, scarcely to be distinguished from those which in other
situations occur in trap, and which are so frequently to be seen in
those traps where nodules of calcareous spar and of chalcedony
are found together.

If we were to reflect on the causes of this gradual change, we
should attribute it to the successive diminution of the proportions
which the other constituent earths of this mineral bear to the silica
which it contains. I need not point out the difficulty of recon-
ciling such a supposition to the general theory of mineral species
and of definite proportions, since mineralogists are already aware
of it, and since many other cases, attended by similar doubts, are
well known. It is a question too important to be discussed with-
out much more numerous and better established facts than those
which we yet possess, and it will hereafter become an object of
serious investigation to mineralogists, when their science shall have
made further progress.

That variety which is called mealy is also here presented under
different aspects, by which its nature is in some measure illustrated.
This condition has, I believe, been generally attributed to the loss
of its water of crystallization, the result of decomposition. It is
obvious however that this is not the cause, since the specimens of
this variety are found in the centre of solid nodules, of the glassy

88 Dr. Mac Cuttocn’s Sketch of the

kind, where neither air nor water can have access, and where they
are accompanied by crystals of absolute transparency: they are
also found intermixed with and investing solid nodules of the
toughest varieties, deeply imbedded in large masses where the
elements are effectually excluded from them. This mealy variety
appears in three different forms: in the first it is disposed in a ra-
diated or rather in a ramose manner, in fine fibres possessing the
peculiar lustre and softness of the finest white pulverulent talc. In
a second case it forms distinct globular concretions of extreme mi-
nuteness, not to be discovered without the aid of the lens; and in
a third instance, which I observed near Loch Eynort, a mass of
globules of solid radiated mesotype, very much resembling some
of the oolites, is intermixed throughout with farinaceous scales of
the same substance, having the greasy aspect and lustre already
described.

In speaking of this substance I have, according to common
usage, ranked it with the mesotypes, it appearing to have been
thus placed, partly because it is found associated with them, and
partly because of the theoretical views which have been held re-
specting its origin. It will be for mineralogists of more authority
to consider whether it does not deserve a separate place as a species:
the question is evidently of a nature not to be determined by geo-
metrical analysis, as far at least as the varieties already found extend ;
and the delicacy and uncertainty of unassisted chemical analysis in
questions of this nature, are far too great to tempt us to seek a
new place for it by this kind of investigation.

The last variety of mesotype exhibits a distinct crystallization ;
but crystals of tangible magnitude are so rare that I only procured
one specimen in which the forms could be determined. They
sometimes consist of a square prism, considerably elongated: in

*

Mineralogy of Sky. $9

one case all the edges of the prism are replaced by planes, while
in another, by the unequal truncation of three angles of a paralle- -
lopipedon, a pentagonal prism is produced. These prisms some-
times terminate in a pyramid, the faces of which correspond to the
planes of the prism, and which is either complete or truncated : in
other cases greater irregularities take place, but the extreme minute-
néss and transparency of the crystals frequently renders it impossible
to ascertain their exact nature.

To compensate for the deficiency of large crystals of this sub-
stance, a profusion of that variety is to be found, which bears a
general resemblance to amianthus, and it is popularly known in
the country by the name of cotton stone. These filaments occupy
the cavities of the trap, and are sometimes accompanied by anal-
cime, as has already been remarked. They vary much in minute-
ness and delicacy, as well as in their state of aggregation, and
hence many variations in their external aspect may be observed.
At times they are placed in distinct straight needles, in other cases
they are crowded into a dense mass, while in a third they are so
entangled as to resemble a lock of cotton wool. Frequently they
have the lustre of common silk, with its apparent dimensions,
while they are in some instances so far attenuated as to resemble
the silk of certain spiders. When the trap has fallen into powder,
they are occasionally detached in light compacted balls, which are
blown away by the winds and float on the surface of the water :
in all these cases the microscope discovers their glassy transparency,
but its powers are insufficient to determine their form, from the
dazzling play of reflected and refracted light which they exhibit. In
some rare instances this variety seems as if it passed into the mealy;
in reality it becomes opaque and puts on to the naked eye a mealy
aspect, which is however readily distinguished by the lens, from

VOL. III. M

90 Dr. Mac Cuxtocn’s Sketch of the

the specimens which I have described above. The last specimens
in point of structure which I shall notice, consist of radiated me-
sotype intermixed with crystals of hornblende, and producing a
compound of an unusual appearance.

The specimens which I have now described are almost invari-
ably colourless and transparent, or white, but occasionally they
assume a brown tinge. One specimen occurred of a sea green
hue and of perfect transparency ; but the flesh colour not un-
common in this mineral did not fall in my way, although found
in the other members of this family which are seen here.

With respect to the exact locality of this substance, I have only
found it at Talisker and at Dunvegan, although it is probable that it
exists In many other parts of this very extensive island, which the
labour of years would scarcely suffice to examine with the scru~
pulosity necessary for this purpose.

It was at Dunvegan that I observed a solitary crystal of
ichthyopthalmite, nor did I succeed in discovering a second. It
appears that laumonite has been also found in Sky: in the course
of my researches I observed some minute specimens of it asso-
eiated with stilbite, but scarcely worthy of notice, unless for this
slender record of their habitat.

Prehnite, a mineral so nearly allied to the zeolites, is also found
in Sky, but it is far from common, while the specimens are at the
same time of trifling magnitude. It occurs in the trap at Portree,
and at other points along the eastern. shore, as well as at Stra-
thaird, in the trap veins which traverse the sandstone, as I have
already mentioned. On the shores opposite to the point of Clachan
in Raasa it is found in a rock, which, although not very common,
occurs in different parts of the western islands. This rock is a
eompound of augite, glassy felspar, and common felspar, the

Mineralogy of Sky. 91

two latter having frequently a greenish hue. Besides the decided
nodules of prehnite contained in it, the same mineral is intermixed
throughout the rock, forming an integral part of it, and often
passing into mesotype, as it appears to do in other more decided.
instances. It has been said by Haily that prehnite has not been
found forming an integrant part of rocks; but as a compound
of a similar nature occurs in the Kilpatrick hills near Glasgow,
an exception must be made in favour of these instances. I may
here add, that a corresponding rock may be seen on the opposite
coast of Raasa.

It is perhaps superfluous to say that nodules of chalcedony, often
hollow and containing crystallized quartz, are occasionally found
in the trap rocks of Sky, stnce they are of such common occur-
rence in this substance. The cavities are sometimes, in addition,
sprinkled with crystals of stilbite, of analcime, and of chabasite.

Of those mineral substances which are the least frequent in trap
rocks, steatite occurs in considerable quantity ; it is tender, and
always of a greenish dirty hue. It is sometimes found in very
small nodules; but in other places, as near Dunvegan and in the
parish of Kilmuir, it is so abundant that it has been dug up with
the intention of exporting it for economical purposes.

I have already mentioned that epidote is found both in the clink-
stone and in the trap, but in too small quantities to render any
further account of it necessary. It is thus far worthy of notice, as
it is one of the few minerals which seems to appertain to rocks of
very different characters and periods of formation.

The carbonate of lime to which I alluded when speaking of the
chabasite, is found in company with this mineral and with the
analcime, occupying along with them cavities in the trap: it pre-
sents but one form, that rhomb which is called the inverse, and

mM 2

92 Dr. Mac Cuxttocn’s Sketch of the

it varies considerably in its dimensions: it is sometimes white, but
most generally of a honey yellow colour, but I must add, that in
either case it is of rare occurrence.

The last and the rarest mineral which I discovered in Sky is
hypersthene. This occurs at Scavig, in that singular variety of trap
which I have already described in the account I gave of the Cu-
chullin hills: it forms veins of different dimensions and much
blended with the rock in which they lie, but they are neither nu-
merous nor large, nor are the veins simple in their composition,
since they resemble the containing rocks in the different substances
of which they are composed. The most prevailing mixture is
however that of hypersthene, and of a dark felspar precisely
resembling that of Labrador in its general aspect, but not pos-
sessing its iridescence. This felspar is frequently crystallized, but
as. the crystals are always completely imbedded, nothing further
of their form can be discovered than the outline which is dis-
played by the fracture: together with the dark felspar, white and
glassy felspar also occurs in the mixture, and the common opake
white variety is sometimes, but more rarely, intermixed with all
the other substances. It has been already noticed that these veins
are traversed by veins of clinkstone and of basalt, and they are

also intersected by veins consisting of common white felspar and
quartz, sometimes confusedly intermixed, and at others disposed
in the graphic form. This opake felspar is sometimes distinctly
crystallized in cavities. Rarely mica occurs in the compound, and
in one specimen I observed transparent green crystals so minute
and so imbedded that their nature cannot be ascertained: they
have the aspect of olivin. Pyrites is occasionally seen, interspersed
among these substances, but it is also rare.

The hypersthene presents specimens of great magnitude and

Mineralogy of Sky. 93

beauty, which, although they seem to resist the injuries of time
far longer than the accompanying substances, at length also be-.
come rotten, and fall into an ochry powder. Distinct concretions
are to be found exhibiting the primitive form, and which appear
to be true crystals, since they are detached from the surrounding
substances. More generally however, it is without form, while
in many cases it is intermixed with the dark felspar so as to pre-
sent the graphic character, the crystals of felspar being defined,
and the hypersthene occupying the interstices. The lustre of this
mineral is always highly metallic, but the specific gravity of the
specimens which I examined did not exceed 3.342. The colour
is various; in general it is of a purplish black, sometimes steel
grey, and more rarely. of a pale whitish grey, while it often as-
sumes the hue, together with the lustre of polished brass, when it
has long been exposed to the air.

Hypersthene has been found in Aberdeenshire, but the circum-
stances which accompany it have not been described, nor the
nature of its connections ascertained. As far as can be determined
by this instance, it must be considered as an inmate of the trap
family. Having also found it in the island of Rum associated with
the same class of rocks, additional confirmation is afforded of this
connexion. That of Labrador is known, like the present, to be ac-
companied by dark felspar; but the rock which is the common
repository of both has not been described by the missionaries,
to whom we are indebted for the only knowledge we possess of
that country. Mr. Giesecké considers the Labrador felspar of
Greenland as belonging to what he calls the “ Syenite formation,”
and it is not improbable that his syenite formation resembles the
rock which I have already described, and that there is a corres-
pondence in the repositories of this substance in both countries,

v4 Dr. Mac Cuitocu’s Sketch of the

Among the rocks, for which I could not find a place in the
geological description without disturbing its order, pitchstone re-
quires to be noticed. Although not found 7 situ it offers as a
mineral specimen some appearances which are interesting, and
which I shall therefore describe. It was on the hill of Glamich
that I found the specimens in question, and it is probable that they
had been detached from some veins which I was unable to trace.
There are two varieties, a black one very little differing from
that of Rum, except that it contains a few dispersed crystals of
glassy felspar; and an olive green one, which as it offers some
apparently important peculiarities hitherto, unobserved, I shall
describe more fully. It is often of a granular combined with a
small conchoidal fracture, and is generally disposed in distinct
concretions which are either of the flat or curved lamellar form.
It is remarkable for containing irregular rounded cavities similar
to those of the amygdaloids, filled with compact grains of a grayish
hue. The structure of these is so singular as to be deserving of
notice. On breaking the smaller ones they are discovered to
consist of a grayish white enamel similar to that which is formed by
the fusion of felspar. But if we break the larger grains we can
distinctly see that the center is composed of glassy felspar, the
crystalline transparency and platy fracture of which are perfect,
while the surface to a certain depth is converted into the white
enamel I have described. I have not observed this very peculiar
and striking appearance in any other pitchstone which has come
under my notice, although there are appearances not much unlike
it in some of the varieties found in Arran.

Those who conceive pitchstone, like basalt, to be of igneous
origin, will have little difficulty in explaining this phenomenon,
and will even find in it strong evidence to support that theory.
It is unnecessary to enter on a reasoning so obvious.

Mineralogy of Sky. 95

I have concluded, perhaps without sufficient evidence, that the
pitchstone both of Ben-na-Caillich and of Glamich, has been -
detached from veins. This deduction is made from the smalk
quantity of fragments which are to be found, and from the circum-
stance that all the pitchstones of Scotland hitherto observed ac-

tually occur in veins.
/

A large portion of the summit of Glamich has the power of
affecting the magnetic needle at even a considerable distance, a
property extremely common in the rocks of this family. I was
desirous of ascertaining if any regularity existed in the position of
the magnetic poles, similar to that which Humboldt has observed
in a rock of serpentine which he has described: for which purpose
I observed the affections of the needle over many parts of the
space as far as that was accessible, and I have represented them in
the accompanying diagram, Pl. 3, fig. 1.

A consideration of those positions in the diagram will explain
immediately that which would require much circumlocution to
describe in words. In five places, extending from the eastern to
the south-western side of the ground included in the circle, it will
be seen that the needle remains uninfluenced. At the northern
limit of the hill its position is equally true, but from the strength
of its polar tendency, I conceive it was there affected by the coin-
cidence of its position with the meridian of some neighbouring
magnet, although by some oversight I neglected to take any other
bearings, near the same spot which might have verified this suppo-
sition, On the north east rhumb in five several places taken at
the distance of five yards from each other, the positions are such as:
could not result from the influence of any one magnet, however

96 Dr. Mac Cuttocn’s Sketch of the

that may be conceived to be placed. This discordancy of position
is still more remarkable in the several parts of a neighbouring line
running on the E. by N. rhumb, and proves clearly that several
magnetic bodies exert their influence in producing the disturbance
which is there visible. Were it necessary to confirm this by any
other observation, it would be fully proved by its deviation at a
distant point situated near the N.W. part of the circle, where its
position is such as to be evidently produced by some magnet un-
connected with those which cause the great irregularities crowded
together in the two places immediately before described. If I
understand rightly the account which Humboldt has given of the
affection of the needle by the hill of serpentine which he describes,
it would appear that the whole rock consisted of a single magnet
acting with great regularity on the needle. But in this case it is
plain that its deviations from the true meridian are the consequences
of the actions of several magnetic bodies dispersed over the summit
of the hill, from the intricacy of whose combined influences it will
evidently be impossible to determine the precise position or extent
of any of them. It is probable that the meridians of all these and
similar magnets occurring in the basaltic rocks, or in other rocks,
are coincident with the magnetic meridian, and that they acquire
this virtue as masses of iron are often known to do by long
continued rest in favourable positions, combined probably with
circumstances of which we are as yet doomed to remain in
ignorance, little acquainted as we are with the history and causes
of this obscure power. But I need not dwell longer on this
particular example, since in a paper on Glen Tilt, ‘which will be

found in the present volume, I have entered at some length into the
general question.

Mineralogy of Sky. 97

Among other matters I have reserved for this division of the
present paper, the very little information which I was able to ~
procure respecting the coal of Sky. Appearances of it are to be
seen in several places in the trap, as I have already cursorily
noticed, and among the rest a solitary mass of some thickness is
' found near Talisker, but in a part of the cliff nearly inaccessible.
It is here as in most similar cases mixed with bituminous wood.
Coal has also been found at Portree, and some fruitless and
expensive attempts have been made to work it. Thin edges
of seams of coal may also be observed in different places in
the parish of Kilmuir, together with the carbonaceous rubbish
which so generally indicates their presence. Under the direction
of Lord Macdonald some borings and examinations have been
made by coal surveyors, but, for reasons of too frequent occur-
rence among the itinerant professors of this branch of surveying,
I found that no dependence could be placed on their reports,
nor did my time permit me to institute such an examination as
would have been required to ascertain the true state of things.
The anxiety of the inhabitants and of the proprietors of the
western islands in general for the discovery of this mineral is such
that they are readily misled into the search, and coal mines have
even been pointed out to me in micaceous schist. Nevertheless it
is not unlikely that the district of Kilmuir may contain coal, since
the sandstone and accompanying strata which I have already
described are such as we should expect to find it conjoined with,
and since in the island of Egg similar strata are actually accom-
panied by very minute lamine of that mineral. But there is no
great probability that this coal, even if it were proved to belong to
these strata and not to the accidental fragments dispersed in the
trap, like the one at Falisker, could be worked: as a matter of

VOL. III. N

98 Dr. Mac Cu.Locn’s Sketch of the

oeconomy, since the perpetual interference of the trap rocks and
the disturbance occasioned by them, would render it too expensive
an undertaking |
Among other substances I have reserved to this place the descrip-
tion of the siliceous schistus which is to be seen at Duntulm, on
account of its partial nature and because its history would have
interrupted the connection of the geological details. I have already
mentioned that the trap found in this vicinity is obscurely colum-
nar, forming high and picturesque ranges of cliffs surmounting the
hills and extending to the sea shore. I have also noticed in general
that beds of shelly limestone and of sandstone, containing shells
and carbonized wood, alternating with shale, are seen under it. But
the most interesting appearance is that of a disrupted portion
of a thick stratum of the schist, known by the name of siliceous
schist, and of that particularly hard and black variety which has
been called Lydian stone. ‘This rock forms a portion of a bed the
base of which is covered by the fragments of the shore, but its visible
thickness is about twelve or fifteen feet. It is surrounded on all sides
by, and lies under, a mass of obscurely columnar trap, the junction
being in many places attended with great confusion, (Pl. 2, fig. 3.)
It is divided into thin laminz, of which the upper ones alternate
with similarly thin laminz of sandstone, precisely resembling those
alternations of shale and sandstone. which are so common and
so well known. It is not indeed till fragments of the rock are ex-
amined in the hand that the spectator can discover that he sees any
thing but a bed of shale alternating with sandstone: but on thus
examining the schist, it is found to be an extremely brittle and hard
substance, of a’black colour, giving fire freely with steel, sharp in
the fragments, and with an obscurely rhomboidal fracture ; this last
character being the only one by which it can be distinguished from

Mineralogy of Sky. 99

the fine grained basalts, particularly such as] have mentioned as occur-
ring in the form of veins in the Cuchullin. The sandstone laminz
possess at the same time the hardness and jaspideous aspect of that
which I formerly described* as lying in contact with the greenstone
of Stirling castle. Considering therefore the analogy of these two
sand-stones both in aspect and position, we may fairly conclude that
they have in these instances been altered from their original tex-
ture, in consequence of the proximity of the trap rock. The alter-
nation of the two substances here described, which have doubtless
been originally shale and sandstone similar to that of the unchanged
specimens which we meet with in various parts of this shore, gives
us an equal right to conclude that the same influence of the neigh-
bouring trap which converted the sandstone into hornstone, also
converted the shale into Lydian stone. This in fact is the position
of every specimen of siliceous schist or Lydian stone which I have
seen in Scotland. In Cruachan, in Raasa, in Shiant, at Talisker,
it forms beds, in contact with and involved in trap, which, from
their connections and positions, appear to have been common clay
slate, in those cases where it belongs to the primitive strata, and
shale in those where it has formed a constituent of the secondary
ones. It is possible also that the gray varieties of this substance
may have originated from slate, and the black or Lydian stone from
shale: additional facts however would be required to prove this
part of the theory.

I have said that the resemblance between this Lydian stone and
fine grained basalt is so perfect that there is no assignable differ-
ence of character save that of the large fracture, a circumstance of
difference perhaps necessarily resulting from the unaltered stratifica-

* Geol. Trans. vol. 2.

Nia

100 Dr. Mac Cutrocn’s Sketch of the

tion of the Lydian stone. Nor is there any reason to doubt this re-
semblance, since the same materials under a different form probably
compose both rocks. Chemical analysis unfortunately offers us no
temptation to try this analogy further, since the variable composition
of basalts as well as of schist, a variation necessarily arising from the
circumstances of their formation, would prevent the possibility of
comparing any two specimens even of the same substance. It may
be an interesting matter of speculation tq inquire by what power the
vicinity of trap operates in influencing the change from shale to
Lydian stone, as well as in producing the much better known
changes which occur in sandstone bordering on trap. If basalts have
been in any case produced by the fusion of beds of slate, the neces-
sary analogy between the Lydian stone and basalt will appear conspi-
cuous, and we have only to consider it as a shale brought into
the state of basalt by fusion, without such further disturbance as to
destroy its original stratification.

Although both the neighbouring sandstone and alternating shale
which have undergone no change from the vicinity of the trap con-
tain shells in considerable abundance, I did not perceive any marks
of them in this bed of Lydian stone. They may nevertheless exist, —
although they escaped my observation. I have little doubt that the
instances of basalt containing shells which have so often been descri-
bed, have sometimes been cases analogous to this: the observers,
attending to the composition rather than to the disposition of the
rock, having easily been led into error from the perfect similarity of
the indurated shale to fine grained basalt. I may venture to point
out these instances as calling for re-examination.

I shall terminate this account of the minerals found in Sky, by
a more detailed description of the marble of Strath, adverting to
those oeconomical uses to which it seems applicable.

Mineralogy of Sky. 101

The following varieties are the most remarkable of those which
are to be seen in this tract.

1, Pure white marble, the fracture intermediate between the granu-
lar and small platy.

2. The same with a scarcely discernible shade of gray.

3. The same with variously disposed veins of grey and black, re-
sembling the common veined marble used in architectural or-
naments.

4, The same with narrower veins well defined, and often reticu-
lated with a great semblance of regularity: very ornamental.

5. The same, distinguished, independently of the veins, by a parallel
and regular alternation of layers of pure white and grayish
white.

G6. White marble variously mottled and veined with gray, yellow,
purple, and light green. This is also a very ornamental
variety.

Marble, exhibiting various mixtures of white, pink, purple,
light green, dark green, and black, of a rich sombre effect,

ro

and highly ornamental.
8. White marble, beautifully mottled and veined by yellow trans-
parent serpentine.

The ornamental coloured marbles here described, scarcely yield
in beauty to many of the similarly constituted specimens of ancient
marbles, and like many of the marbles of Scotland they will be
found to owe their colours to serpentine. This is also the case in
Glen Tilt, at Balahulish, and in Iona. But the most obviously
valuable variety is the white, which seems to possess most of the
qualities requisite for the purposes of statuary.

Few substances in the catalogue of those with which economi-
cal mineralogy is concerned have excited more interest than statuary

102 Dr. Mac Cuttocu’s Sketch of the

marble, from its rarity, its beauty, and its indispensible necessity
in the art of sculpture. It has at different times formed an object
of anxious research in this country, and premiums have been held
out for it by the Society of Arts. It has consequently been found in
various parts of Scotland, as well as in Ireland, but no native speci-
mens have yet been introduced into the arts. As the causes which
have impeded their introduction have hitherto been such as may be
considered adventitious, being of a commercial nature and not
founded on any experience of their physical defects, it has been
hoped that they might by perseverance and time be removed, and
that the statuary marbles of this country might at some future day
supersede the necessity of importing this article. It will not there-
fore be a misplaced inquiry to examine the several properties of those
marbles which have at different times held a place in the estimation
of artists, and to compare them with our own specimens, more
particularly with that of Sky now under review, the most abun-
dant and certainly the most specious of all those which have yet
been found in Britain. The inquiry is the more necessary, as the
several circumstances in which white marbles differ, do not appear to
have been generally attended to, and as an undue value seems in
some instances to have been fixed on our own in popular estimation,
although not in that of sculptors themselves.

The value of this substance in those distant periods when the arts
of Greece. flourished, occasioned an industrious research after a
material in which the sublime ideas of its artists could be embodied,
Accordingly many quarries have been wrought in ancient times, of
which little has descended to us but the names, and a few of the
works which were executed from their produce. These marbles
were of various qualities, and examples of them are still to be seen
in ancient statues, although with regard to many of them, a species of.

Mineralogy of Sky. 103

evidence, often little better than conjectural, has guided sculptors and
mineralogists in their attempts to determine the quarries from whence
they were derived. Among these, the quarries of Paros afforded a
marble (the often quoted lychnites of Pliny) in which it is asserted
that the celebrated Venus was wrought, as well as some others to
which we have not access. But there are many specimens of sculp-
ture in the British Museum which seem to have been executed in
this stone, or in one at least of analogous character.

Of the nature of the Parian marble we are enabled to speak posi-
tively, since some blocks of it have been quarried during the last few
years, and are now to be found in the shops of the sculptors of this
city. The grain of this marble is large and glistening, while at the
same time its texture is loose and soft, and its colour of a yellowish
and watery white. It possesses considerable translucency on the
edges, a quality which, however desirable in statuary marble when of
a fine grain, from the softness which it gives to the outline, only
increases the disagreeable aspect of the Parian, by the angular re-
flections of light which take place on the pellucid edge and sur-
face, from the innumerable faces of the small plates. ‘The specimens
of sculpture which I am about to quote, will exemplify this fault.
It is certain indeed that the Greck sculptors abandoned the marble
of Paros after the quarries of Luna and Carrara were discovered, the
superior fineness and whiteness of these marbles which at present
cause them to excel any with the places of which we are now
acquainted, rendering them also at least equal to the best of those
ancient ones of which the native places are now unknown.

Independently of the injurious effects which the large grain of the
Parian marble produces on the transparent surface of sculptured
works, and the false lights which it thus introduces into the con-
tour, it interferes materially with the requisite correctness of draw-

104 Dr. Mac Cutxocn’s Sketch of the

ing in the lesser works, and is thus inapplicable to the details of
small sculptures in relief. It is nevertheless susceptible of a good
polish, a quality however, of little value in the eyes of the statuary,
and one which in this variety only serves to render the defects of its
texture more apparent. It is also said to have been deficient in
size, since it was so intersected by fissures as to be incapable of
yielding blocks of more than five feet in length. I may add that
in the present state of the public habits with regard to white marbles,
there is no demand for modern works executed in Parian marble.
Its celebrity is consigned to the metaphors of poets.

It will afford satisfaction to those who are interested in the arts to
point out such works in the British Museum as appear to have been
executed in Parian marble, or in one of similar character.

A Cupid bending his bow. This specimen is rather of a finer
grain than the generality. It may perhaps belong to that marble
called by the Italian sculptors marmo statuario, but this question
eannot be determined without a fresh fracture.

A bust of Minerva.

Aratus, a bust. This also is ofa fine grain like the Cupid.

A Venus, of a similar grain, and agreeing with the character of
the marmo statuario. |

Zeno, a bust, of a very coarse grain.

A terminal head of Bacchus.

A terminal head of Mercury.

A Jupiter Serapis.

Bacchus and Ampelus.

Marcus Aurelius, a bust.

There are others, but it is not requisite to enumerate them.

A marble: of a much finer grain, and capable of a high polish,
is described by the ancients, as found near the river Coralus in

Mineralogy of Sky. 105

Phrygia, as well as in some of the Greek islands: it is supposed
to be the variety known to statuaries by the name of marmo-
Greco, and some ancient statues are described as being formed of
this marble. It is possible that specimens of it may exist in the
British Museum, but our sculptors are, as far as I know, incapable
of distinguishing it at present, and it is much too hazardous to
assign the place of a particular specimen from the contemplation of
a polished and often of a stained surface. Mr. Tennant has found
that the marmo Greco is a magnesian limestone.

I am equally unable to point out specimens of that variety
known to the Italians by the name of marmo statuario, of which
the quarries are also lost, but which, with greater translucency of
surface, resembles the Parian marble in the largeness of its grain,
unless those which I have conjectured to belong to this variety,
when describing the specimens of sculpture in Parian, do in fact
appertain to the latter.

The quarries of Luna produce a compact white marble sus-
ceptible of a high polish, and capable of being wrought with the
most minute accuracy. Hence it is preferable for the finer opera-
tions of bas relief, either to the Parian, of which the aspect in-
terferes with the delicacy of finish and of surface required in these
works, or to the Pentelic, which was subject to aecidents from veins
of mica and of serpentine, or to that of Carrara, in which dark veins
are of frequent occurrence. It was accordingly preferred by the
antients, and among many other works, the Apollo (Belvedere) is
said to have been executed in Luna marble. We have no other
knowledge of the marbles of Hymettus and of Arabia than their
names. |

Of all the marbles employed in the works of the antients, and
of which many specimens have descended to our days, that of

VoL. 11. )

106 Dr. Mac Cuttocn’s Sketch of the

Carrara is almost the only one which is at present held in estima-
tion, or is now accessible to modern sculptors. This marble is of a
very fine grain and compact texture; it is also susceptible of a
high polish when required, and is consequently applicable to
every species of sculpture, except when, as is too often the case,
dark veins intrude and spoil the beauty of the work. Notwith-
standing the general apparent uniformity of its texture, it offers
different varieties of aspect. It is always of a fine granular frac-
ture, yet this fracture is sometimes combined with a slight ten-
dency to the flat splintery, in which case the stone is harder and
more translucent than when it is purely granular. When merely
granular it is sometimes dry and crumbly, precisely as if it had
been exposed to a high heat; it then loses much of its transpa-
rency, and is called «weo/ly by sculptors. Its transparency is va-
rious, and in some cases nearly equal to that of alabaster, (granular
gypsum. )

The bust of Marcellus in the Museum offers an example of a
very fine grained and extremely translucent marble, apparently of
this kind. The specimen employed in the bust of Messalina is
equally remarkable for the fineness and beauty of its texture. In
a bust of a youthful Hercules in the same collection the identity
of the marble is marked by the dark veins which are to be seen in
it; but it is unnecessary to quote individual specimens, as the
greatest number of the sculptures in this collection appear to have
been executed in Carrara marble.

The last of the antient marbles which I shall describe is that of
‘Pentelicus, of which the quarries are probably still to be found in
the vicinity of Athens, although they have not been investigated
by modern travellers. But we are in possession of numerous
specimens of sculpture in this stone, from which we are able to

Mineralogy of Sky. 107

determine its qualities ; two are to be seen in the British museum.
Of these there is the bust of a Philosopher, of, apparently, antient ”
and very dry workmanship: the other is the celebrated Disco-
bulus. It is known that Myron the Athenian, who fiourished
about 440 A.C. executed a work of this character in bronze:
but we have no evidence respecting the marble statue, and artists
have therefore remained in doubt whether it was executed by him-
self or was a copy by another hand. This question cannot be
positively decided by the sculpture itself, however high its merits.
In the mean time a step is gained by the mineralogical investigation
of the material, and thus mineralogy is capable of throwing light on
the history of the arts. The substance in which it is wrought must
therefore be considered a sufficient proof of the antiquity of the
copy, if it be such, as well as of its having been executed at Athens,
since the quarries of Pentelicus were abandoned in consequence of
their defects, as soon as those of Carrara and Luna were known.
Although it is difficult or impossible to determine this period, yet
as so few works in Pentelic marble posterior to the time of Phidias
and of Myron have descended to us, it is probable that little use
was made of those quarries after the period of these artists. We
are therefore, perhaps, entitled to conclude that the Discobulus of
the Townley collection is an Athenian work of the best age of
sculpture, and not a copy by any more modern artist ; and that if
it was executed neither by Myron himself nor under his direction,
it is yet not likely to have been much inferior to the original, while
it may serve, at the same time, as some proof of the esteem in
which that work was held at Athens.

But the most numerous examples of Pentelic marble are to be
found in those works of Phidias which form the collection of Lord
Elgin, and which afford easy access to examination. In the

0 Z

108 Dr. Mac CuxtLocn’s Sketch of the

present corroded and tarnished state of the surfaces of these statues,
we cannot trace the nature or the defects of this variety, but an
examination of its texture and composition in the broken frag-
ments, serves to excite the deepest regret, that the genius of the:
greatest sculptor whom the world has seen, should for want of
better materials have been condemned to bestow its energies on so’
perishable and so defective a stone. This marble is of a loose.
texture and moderate sized grain, coarser than that of Carrara, but
finer than that of Paros; in colour it is exceedingly imperfect,
being tinged with gray, brown, and yellow, and mottled with
transparent parts, which give it the appearance of having been
stained with oil. But its most formidable defect is its laminated
structure, and the quantity of mica with which it is contaminated :
to this we are to attribute the corrosion and almost entire ruin of
so many of the specimens, the action of the weather dissolving
those parts of the stone where the mica is most abundant, and
eating deep fissures through many parts of the work. It is pe-
culiarly unfortunate that the two most admirable specimens, spe-
cimens. which are calculated to excite in the minds of artists a
mixed feeling of wonder and despair, the horse’s head and the
Theseus, should be those which have suffered most. Had they
been fortunately executed in the more uniform and durable stone of
Carrara, these works. might still have been preserved to us in all
their original perfection of drawing and surface. Even the ham-
mer of the Turk would have rebounded with little injury from’
the marbles of this texture, while the micaceous stone of Pente-’
licus splitting in the direction. of its laminz, has permitted the
complete mutilation of many valuable sculptures.

. We have no geological information with regard to the relations
of these stones. The great resemblance of the Pentelic marble to

Mineralogy of Sky. 109

that of Glen Tilt in aspect and composition, renders it probable
that like this it lies. in mica slate, forming beds parallel to and inter~
stratified with that rock: that the others have similar relations to the
primary rocks, we should have concluded on general geological prin-
ciples, had we not already seen that the white marble of Sky which
has given rise to this discussion belongs to the secondary strata.

‘We have now to examine the white marbles which have been
discovered in our own islands, for the purpose of comparing their
relative properties and the value which they are likely to possess
in sculpture. I am unfortunately unable to give any account of
those found in Ireland, neither Ramngt seen their places, nor being
possessed of any specimens.

That which has been found at Cape Wrath in Scotland, is of a
grain much larger than even the Parian, and is consequently useless
for the purpose of sculpture; and this indeed is by much the most
common character of the Scottish specimens... Those of Blair-
gowrie, of Glenavon, and of Balahulish, are. all equally charac-
terized by this large sparry texture, and are all equally unfit for
sculpture, however applicable to the purposes of architecture.
The marble of Iona has been long since exhausted, and conse-
quently requires no particular notice: however valuable from the
purity of its colour and compactness of its texture, yet the uncer-
tainty of its splintery fracture before the chisel, (that tool without
which no spirited work was ever finished,) combined with its great
hardness would probably have rendered it useless in the arts, even
if it were still to be procured.

In a paper on Assynt* I have already described the white marble
of that district : it is of a very close texture, and although it con-

* Vol, 2.

110 Dr. Mac Currocn’s Sketch of the

tains no earth but lime, is of unusual specific gravity and hardness.
It is incapable of being polished, a circumstance, it is true, of no
consequence in statuary, since the polish only gives a false light to
the surface and is not admitted of in modern sculpture; but it
labours under the concomitant disadvantage of want of trans-
parency, producing nearly the same dead effect and dry outline
as is seen in a plaster cast, a fault in itself sufficient to prevent
it from ever being adopted as a good material in the arts: its ex-
treme hardness also renders it very expensive to work.

The marble of Sky, the more immediate object of this dis-
cussion, is of a pure white colour, and appears sufficiently extensive
and continuous to be capable of yielding large blocks. The purity of
its colour is seldom contaminated; its fracture is granular and
splintery, and its texture fine, less fine than that of Iona, but more
so than that of Assynt: its compactness, hardness, and gravity, are
greater than those of the marble of Carrara, which it in fact re-
sembles in little else than colour. It is apparently well fitted for
all purposes of sculpture, as it can be wrought in any direction,
and has sufficient transparency, while at the same time it assumes
even a better polish than is required for statuary. With these good
qualities, however, is combined an uncertainty arising from its un-
equal hardness. While some parts of the stone are nearly as easy |
to work as that of Carrara, many other specimens turn out so
hard as to add a charge of near 50 per cent. to the cost of work-
ing: this appears to arise from the influence of the syenitic and
trap veins which traverse it, as I have before mentioned, but which
however produce no change in its chemical composition, nor any
other effect than that of induration. This addition of price to the
current charge of working is sufficient in the harder specimens to
counterbalance in a great degree the superior cheapness of the ma-

Mineralogy of Sky. 111

terial, and the advantages derived from lower freight duty and
insurance. Such are the difficulties which oppose the intro-
duction of the most perfect marble which has yet been found in
Britain, difficulties which, slight™as they are, ought, together with
the prevalence of established habits and of a commercial routine,
to check the extravagant hopes which have been entertained in this
country of superseding by its own produce the importation of
foreign statuary marble. But it will not be rendering justice to the
marble of Sky if I do not add, that it possesses a property not
found in that of Carrara, and one of considerable importance, at
least in small sculptures. This is, that compactness of texture by
which it resists the bruise which so often takes place in marble
at the point where the chisel stops, an effect known to sculptors
by the technical term stunning, and of which the result is a dis-
agreeable opake white mark, generally in the very place where
the deepest shadow is wanted.

I have little to add respecting the marble of Glen Tilt, as I have
spoken of it in another place. Except the somewhat larger size
of its grain, it is scarcely to be distinguished from the Pentelic ; in
colour it is precisely similar; but as the character and defects of
the Pentelic, which I have already given, are equally applicable to
this variety, we may fairly abandon all hope of rendering it b usefa)
in the art of sculpture.

‘IL On the Oxyd of Uranium, the production of Cornwall, together
with a description and series of its Crystalline forms.

By Wi11aM Parties, Member of the Geological Society.

Read February 17th, 1815.

Tn only mine in Cornwall which until within the last few
years was known to have yielded the oxyd of uranium, was that
called Carharack, which was situated about two miles nearly south
of St. Die. The crystals on a specimen from that mine in my
possession are tabular, of a green colour and transparent, except
such of them as are partially or wholly coated by a deposition of
an ochreous substance, similar to that termed gossan by the miner.
This substance also is interposed between an aggregated quartz
tinged with iron, and the crystals; some of which are imbedded in
it. It may therefore be termed, in regard to this specimen, the
matrix of the crystals) On many of them have been deposited
numerous minute cubes of a light green colour; which, as there is
a considerable deposition of cubic arseniated iron ina cavity of
the same specimen, I consider to be that substance rather than the
oxyd of uranium: for though the latter sometimes takes a form so
nearly approaching to the cube as that the eye cannot perceive any
difference, yet such instances are certainly not very common.

In 1805, I noticed some crystals of the oxyd of uranium on the
refuse heaps of Tin Croft mine, which is at the foot of a granitic
hill called Carnbrae near Redruth; the veins of that mine run

Mr. WILLIAM Pui ups on the Oxyd of Uranium. 113

partly through granite, partly through schist.* A further search
enabled me to obtain several beautiful specimens containing many -
varieties in the form of the crystal as well as in colour. The
crystals are for the most part well-defined, but the largest scarcely
exceed half a line-in length or breadth, and some of them. are
accompanied by black pecherz (Uran oxydulé Hatiy); they were
found on, or in the cavities of, considerable blocks of a hard
substance enclosing portions of decomposed felspar; but quartz
formed the principal part of the mass, which had decidedly the
character of being an aggregation resulting from the decomposition
of granite. The specimens in my possession, are for the most part
thinly coated with a black substance which I consider to be the
pecherz in a pulverulent form ; internally they are of a redish hue,
arising probably from iron, with which the mine abounds, and
occasionally some minute rounded portions of iron hematites may
be observed. The depth at which these blocks were found,
according to the best information I could obtain, was about 90
fathoms from the surface, in a copper vein.

I also obtained many specimens containing beautiful and well
defined crystals of the oxyd of uranium from Tol Carn mine,
which is about two miles north of Carharack, and near St. Die.
The veins of Tol Carn mine pass through a decomposed granite,
of which the prevailing substance seems to be felspar, enclosing
portions of quartz and silvery mica. With this substance the vein
seems to have been filled in that part in which the oxyd of |
uranium was found, but it was of a dark colour, and had attained,
though considerably friable, a texture much more firm than that
of the neighbouring country; and as, on almost every specimen,
the crystals of the oxyd of uranium were accompanied by pecherz,

) _ * Geol. Trans. Vol. 2. p. 152. 7 4

VoL, 11. P

114.) Mr. WitiraM Puiiurps on the Oxyd of Uranium,

it seems probable that both its colour and hardness may be ascribed
to the dissemination of that substance throughout the mass, which
leaves a black streak on paper. Some specimens also abounded
with pyrites both arsenical and martial, and some of them have
decomposed since they came into my possession. The veins of
Tol Carn mine afforded little or no copper; the uranium was
found in one of them at about 30 fathoms from the surface.

The colours of the crystals both from Tol Carn and Tin Croft
mines are nearly the same. They vary from almost opake
white to yellowish, and pass into the most brilliant yellow;
some being transparent, others opake. Of some tabular crystals,
the center is transparent and nearly colourless, and the edges are
yellow. On other specimens the crystals are transparent and of a
greenish hue, whence they pass through almost every shade, into
deep grass green; while in others, the center of the crystal is
yellow and the edges only are green. Again, from a brownish
tinge they pass into a rich brown, but as the surfaces of these
crystals glisten, the colour seems to be original; while on many
specimens the crystals, which are of a light green colour, are
hollow at their centers and of an ochreous brown, a circumstance
arising doubtless from decomposition, and which in other speci+
mens has proceeded so far as that the forms of the crystals can no
longer be defined. |

The crystals on some specimens from Tin Croft mine are
accompanied by spiculz of blue carbonated copper; in others, by
green carbonated, and red and black oxides of copper, and on one
specimen, they are deposited on minute spicule of oxide of iron.
I have some specimens of the red oxyd of copper from the mine
ealled Huel Jewel, on which there are very numerous and minute
tabular crystals of the oxyd-of uranium of a light green colour,

Mr. WiLtiAM Puitures on the Ongd of Uranium. 115

and one specimen of wavellite ‘from Stenna Gwyn near St. Austle,
on which some crystals of a light yellow colour are deposited.

But by far the most brilliant specimens of the oxyd of uranium
that have been found in this, or perhaps in any other country,
were discovered within the last three or four years in Gunnis Lake
copper mine. near Callington in Cornwall. The gangue of two
specimens in my possession is of quartz, bearing the characteristic
marks of being the result of decomposed granite, and which is
rather confirmed by the circumstance of its cavities being filled
with grouan, or decomposed felspar, of a flesh colour; of another
specimen, the gangue is wholly a hard gossan. All the crystals
from this mine that I have seen are described by fig. 15; they are
extremely thin, but on some specimens they are more than half an
inch in diameter. They are for the most part lying flat together,
forming fasciculi which interrupt each other at various angles, and.
give an extremely beautiful appearance to the group. In Gunnis
Lake mine the oxyd of uranium was found at about 90 fathoms
from the surface, and in a part of the vein in which gossan
abounded. On the few specimens in my possession from that mine,
I have not noticed any trace of pecherz, but on those from Tol
Carn and Tin Croft mines, particularly the former, it prevails
very much. It is sometimes of a resinous transparency, but
is. more generally of a dark brown or black, either amorphous or
in globules: on several specimens from Tol Carn mine it is quite
friable. . 7

_It has already been said that the crystals of this substance from
Tol Carn and Tin Croft mines, from which:the drawings of the
accompanying series were made, are for the most part very smail ;
all the larger ones are so deeply striated in a horizontal direction, as

P2

1169 - Mr. Wittram Puivurps on the Oxyd of Uranium.

to:present the appearance of distinct tabular depositions progressively
altering in size; and these are easily separated in the direction of the
strie, by that means discovering occasionally a thin ferruginous
deposit between them, but-not extending to the edges of the tables.
Those crystals which are so small as to merit the term minute,
though of a thickness nearly equal to their breadth, particularly
those of a deep green colour, rarely exhibit the horizontal striz on
their lateral planes, which are perfectly brilliant: yet I have not
been able to find one that could satisfactorily be submitted to the
reflecting goniometer. On the measurement of the angles of the
oxyd of uranium, it is therefore impossible for me to offer any thing.

The ease with which the crystals of this substance are separated
parallel with their terminal faces, was long since noticed by the
Abbé Hawty, who adds that its other cleavages can only be
perceived by the assistance of a vivid light. The Comte de
Bournon who acknowledges much attention to this substance, says
(Cat. p. 340) that by the assistance of a strong light, he could
perceive indications of cleavages in the directions of both the
diagonals of a tetrahedral prism (Fig. 2 or 3), which by both these
scientific mineralogists is adopted as the primitive form of the
oxyd of uranium. I have very satisfactorily obtained cleavages
parallel with the lateral planes of that solid.

The authors above cited do not however agree in regard to
the height of the prism which both have assigned as the pri-
mitive form of this substance. The former of them has supposed
that the height is to the breadth, as 16 to 5, while the Comte de
Bournon considers that there is some, though not conclusive
evidence for adopting a tetraedral prism with square bases much
less in height than that assigned to it by the Abbé Haiiy. It is
hot in my power to offer any thing decisive of this question, for

Mr. WiLi1aM PuHiLiips on” the Oxyd of Uranium. 117

as it depends, in the first place on the precise admeasurements of
certain angles, which no crystal I have hitherto seen has enabled -
me to make, and in the second place, on calculations founded
thereon, for which I possess not the requisite qualifications, I am
compelled simply to state the opinions of these crystallographers,
and shall be amply gratified if, in their estimation, what is now
offered in regard to cleavages not before obtained, and modifi-
cations not before noticed, shall tend to throw any light on this
important part of the subject.

The occasional notice of what appear to be perfect cubes, added
to the certainty that cleavages are practicable parallel with every
plane of that solid, at first tempted me to presume that it ought to
be considered as the primitive form ; but the consideration of some
circumstances connected with the crystallization of this substance,
induced me wholly to abandon the idea. The inspection of the
annexed drawings will evince that, of the five modifications
described, the first alone is compatible with the cube.*

All the crystals represented in the accompanying series which
are so remarkably flat as to have the appearance of mere lamina,
are from Tol Carn mine, which yielded only such as are of that
description, while on the other hand, the greater part of those from
Tin Croft mine nearly approach in height the dimension of the
cube, or exceed it. A considerable proportion of such as are
rather less than that dimension exhibit no striz on the lateral
planes, which are very splendent: many of those which are deeply
Striated on these planes are iridescent on the surface. The

* In reply to this observation it may be said that the plane which constitutes the third
modification of the annexed series, also occurs on cubes of fluate of lime and sulphuret of
iron; but on these two substances, which are remarkable for the beauty and elegance of

their crystalline forms, that plane only appears in combination with two. other similar
planes, placed on the edges, and replacing the solid angle of the cube.

118 Mr. Wri1iaM Puiuiies on the Oxyd of Uranium.

crystals from Tol Carn mine are generally of great length and:
remarkable transparency, those from Tin Croft are more generally
opake ; but the long and slender crystals from the former mine
rarely suffer interruption from each other, being generally. de-
posited at right angles, and thereby shewing a constant tendency
to assume a quadrilateral figure.

- There are in my possession about 55 specimens of the oxyd of
uranium from the various mines in Cornwall above cited, and up-
wards of 200 detached portions, each having one or more well.
defined crystals on them and placed on pieces of wax; from these
the accompanying drawings were made. PI. 5, 6, and 7.

Varieties of the Primitive Crystal.

It has been already noticed that the primitive crystal of the
oxyd of uranium is considered to be a tetraedral prism, with
square bases. I have never observed any crystal, exhibiting the
primitive planes only, of a greater elevation than that_ described
by fig. 1. Fig. 4 represents an elongated crystal: this elongation
ig so considerable on several crystals from Tol Carn mine that.
the length exceeds the breadth many times.

First Modification.

The first modification is the result of a decrease along the lateral
edges of the primitive prism, by which each is replaced by a
quadrangular plane.* The crystals represented by figs. 6, 7, and
8, are the most common of the whole series.

* The Count de Bournon in his ‘ Catalogue” has described a modification which I
have not been fortunate enough to discover on any crystal from Cornwall, whence every
crystal delineated in the annexed series was brought. The planes of this modification he
describes as being in combination with that above quoted as the first modification, and as
replacing the lateral edges of that plane by quadrangular planes.

Mr. WiLt1AM Puixurps on the Oxyd of Uranium. 119

Second Modification.

~ This modification consists in a decrease on the terminal edges of
the primitive prism, by which each is replaced by a trapezoidal
plane, inclining more:on the lateral than on the terminal faces ;
and, as will be obvious on consulting the planes of this modifica-
tions numbered 2.2, on figs. 23 and 24, tending to produce a
very acute octohedron. On the crystals described by figs. 13, 14,
15, and 16, the lateral primitive planes have wholly disappeared.
The lines on fig. 9 shew the striz, which, on the larger crystals,
are not only visible, but’ deep. self

Third Modification.

The third modification consists in a decrease on the solid
angles of the primitive prism, by which each is replaced by
an isosceles triangular plane, inclining more on the lateral edge
than on the terminal face, fig. 17. The length of the crystals
delineated by figs. 23 and 24, which shew the approach to the
acute octohedron, would, if the apices of the crystals had been
complete, have equalled at least four times their breadth ; they
are deeply striated in the direction shewn on fig. 9. T possess
a crystal delineated by fig. 24, on which the planes 2.2, are per-
fectly brilliant and well defined. Fig. 31 shews the combination
of the planes of this with those of the preceding modifications
and of the primitive prism. On the crystals described by the four
last figures in the series of this modification, two of the four
planes of the second modification have disappeared on each pyra-
mid, giving to their common base and to their terminal faces the
form of triangular planes.

120 Mr. Witi1am Putturps on the Oxyd of Uranium.

Fourth Modification.

This modification, like the preceding, consists in a decrease on
each solid angle of the primitive prism by an isosceles triangular
plane, but which, instead of being placed, as in that modification,
more on the lateral edges than on the terminal faces, inclines more
on the terminal faces than on the lateral edges. On the crystal
represented by fig. 42, the planes of this modification are per-
fectly brilliant.

Fifth Modification.

By this modification the terminal edges of the primitive prism
are replaced by trapezoidal planes tending to form an octohedron,
fig. 46. The succeeding figure shews the planes of this, in com-
bination with those of the second modification, or the acute
octohedron. The crystals described by figs. 46 and 47 are nu-
merous, brilliant, and well defined: they rarely exhibit any lateral
striz, but are so minute as to render it impossible even to approx-
imate the real admeasurement of the angles formed by the meet-
ing of any two of their planes. An attentive examination induces
the belief of their being somewhat more obtuse than the regular
octohedron ; and they are so delineated.

Ill. On the Geological Features of the North-eastern
Counties of Ireland,
Extracted from the Notes of J. F. Bercer, M.D. M.G:S.

4 ‘ Read April 15th, 1814.

With an Introduction and Remarks,
By the Rev. W. Conyzzare, Member of the Geological Society.

Read April 5th, 1816.

INTRODUCTION.

To collect in one point of view the general results deducible
from the ensuing detached observations, and enable those who
may be unacquainted with Ireland to follow their course with
greater facility, it seems desirable to introduce them by a rapid
survey of the general features which distinguish the district they
refer to.

That district may be described as limited by Dundalk bay on
the S.E. and by Lough Foyle on the N.W. including towards the
south the counties of Down, Armagh, and the N.E. angle of Lowth
lying between Dundalk and Carlingford bay; and on the north,
Antrim and Derry: that portion of Tyrone which extends along
the S.W. shore of Lough Neagh, between Derry and Armagh,
being also comprehended as falling within the same general outline,
' This district is marked by three distinct systems or groups of
mountains, one of which occupies the more southern counties;
while the more northern are divided between:the two others.

VOL. III. Q

122 The Rev. W. ConyBEARE on the

lst System. The Mourne Mountains.

The Mourne Mountains form a well defined group extending
from Dundrum bay to Carlingford bay in the southern extremity
of Down.

Slieve Donard is the highest summit of this group; it has been
said to rise 3150 feet above the level of the sea, but the estimate
of Mr. Fempleton,* who assigns only 2590 as the elevation of the
highest points of the Mourne Mountains, appears more correct, and
nearly agrees with that of Dr. Berger, who calculates its height at
2654 feet.

To the west of the main group the Fathom hills, Slieve Girkin
or the Newry Mountains, and Slieve Gullen, all situated in the
south-east of Armagh, and the Ravensdale and Carlingford Moun-
tains in the north of Lowth, may be considered as its appendages.

Granite is the prevailing constituent of all these ranges.

To the north of the Mourne Mountains Slieve Croob composed
of syenite, and Slieve Anisky of hornblende rock, both situated in
the county of Down and barony of Lower Iveagh, constitute an
elevated tract dependent upon but placed at some distance from the
main group.

Hornblende rock and primitive greenstone are abundant on the
skirts of the granitic district. Mica slate has been noticed only in
one instance. Exterior chains of transition rocks. advance far to
the west and north of this primitive tract, extending westwards
across Monaghan into Cavan and on the north-east to the southern
cape of Belfast Lough and the peninsula of Ardes.

The primitive nucleus bears but a very small proportion in
superficial extent to these exterior chains, which are principally
occupied by greywacke and greywacke slate.

* Mem. R. I. Academy, vol. 8.

Geological Features of the North-east of Treland. 123

It is highly worthy of observation that the points of the coast of
Scotland immediately opposite the Peninsula of Ardes, where the —
greywacke terminates abruptly on the Irish side of the North
Channel, present in the neighbourhood of Port Patrick and through
the greater part of the Mull of Galloway, a resumption of the
same formation; nor is the analogy in the structure of the two
countries confined to this one point. The hills of the Mull of.
Galloway are a branch of the great chain of mountains which
under the name of the Lead hills and other local titles, traverses
the whole of Scotland on the south reaching from sea to sea, and
the composition of this chain agrees through its entire extent with
that of the mountainous tract just described, the transition rocks
forming its predominating constituent, enveloped by which several
small districts of granite occur, as in the hills of Cairnsmuir and
Criffel; while the whole is distinguished from the great northern
chain of mountains or Grampians, by the rare occurrence or total
absence of mica slate, which in the latter is remarkably prevalent.

On the north of the Mourne Mountains rise the Bann one of
the tributary streams of Lough Neagh, and the Lagan which flows
into the estuary of Belfast; and on the south several small rivulets
which run immediately into the sea, the base of the mountains
being in that direction washed by the Irish Channel.

2d System. Primitive Chain of Londonderry.

The mountain group which I have thus designated, rises at the
distance of about 50 miles to the N.N.W. of the external chains of
the first system. .

It forms a large mountainous tract comprehended between the
river Roe and the Strabane, partly situated in Derry and partly in
Tyrone. Q2

124 : . The Rev. W. ConyBEARE on the

From its southern boundary it emits two water courses; the
Mayowla which takes an eastern direction and flows into Lough
Neagh; and the Moyle which passes to the west and joins the
Strabane river.

On the north the Fanghan waters a beautiful valley, at length
discharging itself into Lough Foyle.

Sawell is the highest point of this group: Dr. Berger has fixed
its altitude at 2257 feet above the sea. The whole of this extensive
and lofty tract is primitive to the very front towards Lough Foyle.
Mica slate is the predominating rock, constituting exclusively almost
nine-tenths of the district ; it is accompanied by primitive limestone
in the lower part of the country.

On the eastern bank of the Roe this system of mountains is
succeeded by a range of secondary heights, covered by an enormous
platform of basalt and forming a part of that system which will in
the next place be described. ‘These secondary masses repose upon
and conceal the mica slate in the eastern part of Derry, but the mica
slate again emerges from beneath this covering, after an interval of
near 30 miles, in the N.E. of Antrim, and swells into mountains
which break down abruptly towards the coast between Tor Point
and Cushenden bay. ,

The exact correspondence in structure of the opposite points of
Treland and Scotland here again demands our observation; the
Mull of Cantire which faces Tor Point resuming the chain of mica
slate which was there broken off. The Cantire hills are connected
with the Grampians, a chain strikingly similar to that which has been
above described in all the circumstances of its composition; and it
may be added, as compleating this analogy, that the mica slate of
Ireland is succeeded on the south (avhere the Antrim coast exhibits
it in section) by a conglomerate, perfectly resembling that which is
so well known as skirting the Grampians on their southern border.

Geological Features of the North-east of Ireland. 125

We have therefore strong grounds for believing, without incurring
the charge of generalizing too hastily, that the two mountain systems”
described, should be regarded as prolongations of the great northern
and southern chains of Scotland, the former distinguished by the
prevalence of mica slate, the latter by that of greywacké.

In the eastern part of Tyrone which intervenes between these
two systems of mountainous ground, a coal formation occurs
associated with that variety of limestone which is usually found
underlying or alternating with the coal measures in Great Britain.

The position of this coal field offers a new analogy with Scotland,
where the interval between the southern and northern mountains is
principally occupied by a broad zone of rocks connected with the
coal formation, upon which are placed those vast overlying masses
of trap formation which constitute the Campsie hill, the Ochills, &c.
and which, again, correspond both in their constitution and position,
with the basaltic group which forms our third system.* Before

* The assertion that the basaltic group of Ireland corresponds in constitution and
position with that of the Campsie hills, Ochills, &c. requires perhaps to.be stated moie
distinctly, and more in detail; and in the first place with regard to the correspondence
of these districts in the internal constitution of the component rocks. From the description
of the Ochills given by Mr. Mackenzie in the 2d volume of the Wernerian Transactions,
it appears that the prevailing rock is a variety of floetz trap, possessing characters inter-.
mediate between basalt and clinkstone, occasionally exhibiting columns, passing into
greenstone, and in places associated with amygdaloid. Beds of claystone porphyry, of
felspar porphyry and of compact felspar cap some of these eminences. The Campsie hills.
have been ably but more generally described by Col. Imrie in the same publication ;
he represents them as universally covered by a thick mass of floetz trap, divided into beds,
partly amorphous and partly columnar. The trap formation of the north of Ireland consists
principally of basalt divided into beds, partly amorphous and partly columnar ; the latter’
variety resembles clinkstone in the property whence that rock derives its namé; the basalt
passes into greenstone, as may be seen in the mountain of Slievemish and other places,
and it alternates with amygdaloid. A formation of clay porphyry also occurs in the center
of the basaltic area.

In the second place, with regard to the position of the Scotch and the Irish trap districts,

126 ' ° The Rev. W. CONYBEARE on the

describing that system, it is necessary to observe that another small
coal field occurs at Ballycastle, near the edge of the mica slate
district in the north-east of Antrim. |

there are points of agreement and points of difference: the great features of agreement are
those mentioned in the text, namely, that both occur in the vicinity of coal fields, and in
a position intermediate between the northern and southern mountain chains. The points
of difference are, that the Campsie hills seem, at least along their southern border, te
repose immediately on the coal measures; and the same observation may be applied to
the junction of the Ochills with the coal field of Clackmananshire at Westertoun.
Whereas the basalt of Ireland is generally separated from the coal measures by several
intervening beds of considerable importance and of much more recent formation, which
appear to be altogether wanting in Scotland. It may be even objected to the instance
of Cross hill near Fairhead, which is cited towards the end-of this introduction as an
example of the occurrence of trap in Antrim under the same conditions with that of
Scotland, namely, in contact with the coal measures, that the trap in this instance and
through the whole range of Fairhead, assumes a character so widely different from the
compact and small grained basalt of the neighbourhood, (being a highly crystalline green-
stone) as almost to warrant the suspicion of its being a distinct formation, notwithstand~
ing its close geographical proximity to the great basaltic mass. I confess myself however
to be fully persuaded that this suspicion will on further examination be found groundless.
The rock in question closely agrees in its texture with that of Slievemish, which it is quite
impossible to detach from the general mass of trap. The island of Arran appears to form
an important link in the connection I have endeavoured to trace, between the opposite
coasts of Ireland and Scotland ; the center of this island is occupied by a primitive district,
comprising granite, mica slate and syenite ; the mica slate extends to and skirts the N.W.
coast. The N.E. coast presents a small coal formation precisely analogous to that of Bally-
castle, with beds of breccia and of red sandstone resembling those which occur in the Antrim
coast near Newtown Glens; this sandstone forms the prevailing substratum through the
whole south of the island, where it is covered by a singular columnar clay porphyry, and
by greenstone, both of which rocks are generally referred to the floetz trap series. It
seems probable that the porphyry which occurs on the opposite coast of Cantire at Devar
near Campbelltown, and the syenitic rock which forms the crag of Ailsa may be considered
as connected with these formations. The whole island is traversed by numerous dykes of
basalt and pitchstone. A similar structure is continued through the corresponding portions
of Bute. And an exact resemblance prevails between the northern and southern districts
of these islands and the opposite coasts of the estuary of the Clyde in which they are
situated ; thus the primitive rocks, forming the north of those islands, are resumed on the
north of the estuary in Cowal and Cantire ; while the sandstone, breccia, and trap rocks of
their southern district are continued in that direction through the Cumbray isles, and at
Largs and the whole southern bank of the Clyde: the line of junction between these

Geological Features of ihe North-east of Ireland. 127

8d System of Mountains. The Basaltic Group.

This group may be more accurately described as separated into
two chains, bounding on the east and west the trough or valley
through which the river Bann flows from Lough Neagh to the
ocean.

The eastern chain lies in the county of Antrim, being compre-
hended between the valley of the Bann and the Northern Channel.
It presents an abrupt declivity towards the east, falling with a gentle
slope towards the west, in which direction the beds composing its
mass dip.

The hills of which it is composed are generally detached and
distinct, but yet so closely grouped together that there can be no
impropriety in considering them as parts of a single chain.

According to Dr. Berger’s measurement Kock-lead in the north-

secondary and primitive formations seems to pass near the southern extremity of the
Peninsula of Cantire, where a small secondary district, containing, like that of Arran,
some indications of coal eccurs near Campbelltown. See Jameson Mineral of Scottish
isles, vol. 1. p. 134.

Whether any connection can be traced between the floetz trap of Ulster and the
extensive deposits of similar rocks in the islands of Sky, Egg and Mull, is a question
which will be examined with greater advantage when the geology of these islands
has been further elucidated by the able descriptions of Dr. Mac Culloch. It should appear
that in these islands strata of shell limestone containing belemnites and ammonites, and
appearing to be of more recent formation than those associated with the coal fields of the
main land, occur; hence we may perhaps be led to expect that they will be found to exhibit
a still nearer approach to the structure of the hills which constitute our third system.
Towards the west, the limestones and sandstones associated with the coal formation extend
from the banks of Lough Neagh to those of Loch Corrib in Connaught, passing by Lough
Erne and Lough Allen; but the overlying trap is confined to the district described in this
paper, with one trifling exception which is presented by the Corliew mountains in
Roscommon, two miles to the north of Boyle, where the sandstone is covered by a cap of
greystone: the structure of these hills, therefore, agrees still more nearly with the trap
ranges of Scotland than does that of the great Ulster group.

128 The Rev. W. ConyBEARE on the

ern extremity of the chain is the highest summit, it rises 1820 feet
above the level of the sea; but the basis of this mountain is occupied
to the height of 500 feet by primitive rocks, (connected with that
district of mica slate which has been before mentioned as appearing
in this part of the country) leaving only 1320 feet for the thickness
of the secondary strata peculiar to this system. Diris hill, near the
southern extremity of the chain, is wholly composed of those strata
and attains an elevation of 1475 feet above the sea: it is situated
about two miles to the west of Belfast.

On the S.E. this chain pours several small streams into Belfast
Lough, and on the N.E. into the North Channel ; all these have a very
short course. On the west three rivers of rather more importance
take their rise; the six mile water and the river Main which flow
into the bay of Antrim in the N.E. angle of Lough Neagh; and the
Bush which empties itself into the ocean a little west of the Giants
Causeway.

The western chain included between the Roe and the Bann forms
the exact counterpart of the former, but the strata here dip in a
nearly contrary direction, namely, towards the north-east; the fall
of the hills being gradual in this direction, while they front the west
and south with abrupt and precipitous escarpments. Cragnashoack
at the southern extremity, is as might be expected from this general
inclination of the line, the highest summit, it rises 1864 feet above
the sea, exceeding by 44 feet the loftiest point of the eastern chain.
Slieve Gallion, an insulated hill which stands in an advanced position
at some distance from the south bank of Cragnashoack is less elevated
by 240 feet.

Benyavenagh, the extreme mountain on the north, is one of the
lowest in the chain, rising only 1114 feet.

__ The Roe, the Clady, and Aghivey, are the principal water courses

Geological Features of the North-east of Ireland, 129

this chain sends forth ; the two latter are feeders of the Bann, the
first empties itself into Lough Foyle.

The geological constitution of this third system is highly important
and interesting, it is as has been already observed, wholly secondary
and uniformly covered by enormous stratified masses of basalt; this
covering appears to acquire its greatest thickness on the north. The
basaltic cap of Benyavenagh, the most northern summit of the
western chain measuring more than 900 feet ; and that of Knock-lead,
similarly situated in the eastern chain 980 feet: the average depth
of this superstratum may therefore be safely estimated at 545
feet, and its superficial extent at 800 square miles, a solid mass of
extraordinary and imposing dimensions.

In the strata underlying the basalt, the English geologist is
agreeably surprised to recognise many of the most important of those
formations, which reposing upon the coal measures, occupy such an
extensive tract in the south and eastern counties of his own island ;
but which’in Ireland are entirely confined to the comparatively
small district now under consideration, never extending far be-
yond the circumference of the great basaltic area; a circumstance
which almost naturally leads to the conjecture that they may have
been originally much more extensive, but have been elsewhere
removed by the agency of some destroying and denuding force,
to which in this quarter alone an effectual resistance was opposed
by the firm and massive superstratum of basalt which covered
and protected them.

The beds alluded to occur in the following order, proceeding
from beneath the basalt downwards.

1, Chalk:—This formation, which in England cannot be estimated
at less than 800 feet in thickness, does not in Ireland average more
than 200. It agrees exactly with the lower beds of the English

Vou, t11 R

t36 The Rev. W. CoNYBEARE on the

chalk, as seen in the Isle of Wight and Isle of Purbeck, which are
distinguished from the higher beds of the same formation by their
very supesior consolidation. It is impossible for any two portions
of the same formation to be more entirely identified, by every.
external character and by the fossils and organic remains contained
in them, than are these Irish beds, which have been frequently called
white limestone, with the English chalk in the above places : there as
in England the lowest beds are destitute of flints which the upper
contain in abundance.

2. Mulattoe, an arenaceous sione, with a calcareous |cement,
of a speckled appearance (whence its name) derived from numerous
disseminated spots of green earth. It agrees altogether in its cha-
racter and fossils with the green sandstone, which occurs in a
similar geological position underlying the chalk in England: the
thickness of this deposit appears to vary very considerably, and
has not in any instance been precisely ascertained.

The numerous beds of coarse calcareous oolites, which in Eng-
land succeed this green sandstone, are entirely wanting in Ireland,
and the mulattoe reposes immediately on the lias limestone.
Analogous circumstances are not however wanting in England.
In the neighbourhood of Lyme Regis, in Dorsetshire, the green
sandstone has extended itself over the outgoings of the oolites,
rests upon the lias in a manner similar to that just described;
and as it is covered with beds of chalk, the whole section affords
an exact counterpart to that presented by the Irish series.

3. Lias Limestone, a blue argillaceous limestone disposed in
thin beds, alternating with slate clay, and distinguished by the am-
monites, gryphites and the remains of the pentacrinus, which it
abundantly contains. It may be worthy of remark that the sec-
tions given by Guetard and Monnet in the Atlas Mineralogique de
Ja France, and the accompanying description, clearly prove the

Geological Features of the North-east of Ireland. 131

existence of this formation near Metz. Its thickness in Ireland has
not been ascertained.

4. The lias in Ireland reposes, as in England, on beds of red and
variegated marle, containing gypsum and further distinguished by
numerous salt springs; the marle is underlaid by a thick deposit of
red and variegated sandstone containing clay galls. These four
formations which, together with the basalt, constitute the whole
mass of the mountains belonging to the third system, cannot be
estimated as possessing a less average thickness than from 800 to
1000 feet: the whole system appears at the north-eastern and south-
western extremities to repose upon the coal formation, and its
associated limestone, and this again on transition or primitive rocks.

The four formations, more particularly specified, vary conside-
rably in thickness in different places. The mulattoe and lias are often
entirely wanting, so that the chalk rests on the sandstone No, 4: this
position seems to arise from the ‘superior stratum in such cases
extending beyond the outgoings of one or more of the inferior strata,
and being thus brought into contact with beds which, when the series
‘is full, occupy a yet lower place.

The chalk and sandstone are however remarkably constant ; it
may indeed be said to be almost universal within this district ; one
exception, however, is afforded by Cross hill a little to the west of
Fairhead, where the basalt overlies even these, and reposes imme-
diately on the regular coal measures of the Ballycastle district.

The section presented at this point is also worthy of mention,
on account of its general resemblance with that of a part of
the Campsie hills, published by Col. Imrie in the Wernerian Soc,
Trans. Vol. 2, The whole series may be examined with the great-
est advantage in the neighbourhood of Belfast, where all its mem-
bers occur.

R 2

132 The Rev. W. ConYBEARE on the

The proofs which the deep vallies, separating the detached emi-
nences characteristic of this system, afford of their formation by an
agent which has excavated and scooped out as it were portions of
the solid strata, have been most ably and clearly detailed by Dr.
Richardson in the appendix to the Statistical Survey of Antrim.
The general appearances he describes are common (it should be re-
marked) to the vallies of all countries composed of nearly horizontal
strata ; but one phenomenon, as stated by him, seems almost peculiar
to Antrim, namely, that the materials so removed have been en-
tirely carried off, leaving no traces behind them. This circumstance
seems to incline Dr. Richardson to consider the agent which has
acted in the manner described, as some unknown and undiscoverable
cause, and to hesitate in receiving the common and surely probable
opinion. which regards diluvial currents as presenting a satisfactory
solution ; but it must be remembered that the solitary instances he ad-
duces can never weigh against the great majority of cases in which
the fragments of the rocks so destroyed not only occur in abundance
where they might be expected, but exhibit the most unequivocal
marks of their having experienced the action of agitated waters.
He who has examined the valley of the Thames from its source
downwards can be at no loss for illustrations of these positions,
the vast deposits of waterworn debris of oolite which this valley
presents where it traverses the range of hills occupied by this rock,
and those of flint pebbles where it crosses the chalky hills of the
Chilterns, will instantly occur to his mind. It is surely more phi-
losophical to suppose that the violence of the currents has swept
away the debris of the Antrim excavations into Lough Neagh on ‘the
one side, and into the sea’ on the other, than that these excavations
owe their origin to some unknown cause, distinct from that’ which

appears to have produced all others.

Geological Features of the North-east of Ireland. 133

It should be added, that in the county of Londonderry water-
worn fragments of basalt really occur in considerable quantity,
particularly near the valley of the Roe.

It is impossible to dismiss the subject of denudation without re-
marking, that appearances analogous to those so forcibly described
by Saussure as occurring in the Jura mountains, (where scattered. .
fragments of the alpine rocks attest the subsequent excavation of
the great valley now separating the two chains) are also presented,
though on a much smaller scale, among the hills we have just ex-
amined, where rolled fragments of primitive rocks are often found
on the summit of high basaltic ridges, which are at present cut off
from all communication with the primitive districts by numerous
intervening valleys. . (See Sampson’s Statistical Account of the

County of Londonderry. )

134 Dr. BERGER on the Geological Features

§ 1. On the Geological Features of the North of Ireland.

The arrangement adopted in the following observations is, that
suggested by the geological position and relations of the rocks

described.
f A. Granite.
| B. Gneiss and mica slate.
I, Primitive Rocks. | C. Primitive limestone,
D. Primitive trap.
E. Porphyry.
LF. Syenite.

A. Granite.

In the Mourne mountains and adjoining districts an extensive
formation of granite occurs, but neither here nor elsewhere in the
north of Ireland can we recognize the same varieties of that rock
which the mountains of Wicklow present.

The granite now to be described seems rather to agree in its cha-
racters with the newer granite of the Wernerians, a rock sup-
posed to be closely allied to syenite. It appears to constitute almost -
the whole mass of the Mourne mountains, whence it passes across
Carlingford-bay into the county of Louth, extending to the summit
of the Ravensdale mountains. It soon crosses the limits of Louth
to enter into Armagh, composing part of the Faughel hills, whence
it expands itself into a flat and elongated ridge, well known under
the name of Slieve Gulien, forming likewise the Slieve Girkin
or Newry mountains, and the lower and upper Fathom hills, of
which the latter keep close to the right bank of the Newry river.

On the north-west side of the Mourne mountains, where they

of the North of Ireland. 135

slope gradually into the plain, the same rock reaches Rathfriland, a
table-land of inconsiderable elevation.

Within the geographical boundaries just assigned, the granite is
spread over a surface that measures 324 square English miles, com-
prehending the highest ground in the north of Ireland.

A few masses of other unstratified rocks, of which notice shall
be taken elsewhere, occur in this formation.

Some primitive but stratified rocks also rest upon it in many
places, generally arriving at their greatest elevations on their south-
western boundaries.

The texture of this granite is ‘either porphyritic or finely
granular. The felspar always appears the prevailing ingredient,
usually grey, more rarely milk white and earthy ; the quartz has a
smoky tinge, and in the granular variety it generally occurs crys~
tallized in double six-sided pyramids; the mica is of a brown-black
colour, and bears but a very small proportion to the other two con~
stituents.

Amongst the accidental ingredients I remarked but two, Viz.
- crystallized hornblende, chiefly abundant in the porphyritic variety,
and small redish garnets in the granular. ‘The two varieties are, I
believe, mingled both together, so at least they occur on the top
of Slieve Donard. I more particularly noticed the granular on
Slieve Muck, Slieve Birna, Ravensdale, and Slieve Gullen; the
porphyritic on Newry and Fathom mountains. The imbedded
crystals of hornblende cause this rock to act on the magnet.

Water-worn pebbles of porphyritic syenite, occasionally contain-
ing flesh red crystals of felspar and iron pyrites, are very frequent
at the base of the Mourne mountains on the road from Ross Trevor
to New Castle. It is probable that these have been derived from
the disintegration of neighbouring masses of that rock, occurring

136 Dr. BerRGER on the Geological Features

as subordinate beds in this granitic formation ; since on the shore at
Glass Drummond, a ledge of porphyritic syenite, evidently con-
nected with the granitic mass of the adjoining mountain, is seen
running out into the sea.

If the granitic formation, above described, be identified with
the newer granite of the Wernerians, it may be conjectured that it
reposes on mica slate.

B. Gneiss,

. Has not been noticed as occurring within the district now des-
eribed, although the mica slate in the north-east of Antrim some-
‘times assumes a character which it is not easy to distinguish from
that of this rock,

B. 2. Mica Slate.

Of all the primitive rocks mica slate appears to be the most
widely distributed over the north of Ireland.

In Armagh, the sides of that narrow valley which separates
‘Slieve Gullen from the Slieve Girkin mountains, and contains the
“small lake of Cum Lough, are principally composed of mica slate.

In the north-eastern angle of Antrim, mica slate forms the pre-
vailing substratum through a district comprising about 40 square
English miles, and extending from north-west to south-east, between
the mountain of Knocklead (south of Ballycastle) to the valley
‘of the little river of Glendun, which empties itself into the sea at
‘Cushendon, on the north side of Red Bay.

Within this district, however, extensive deposits of very recent

of the North of Ireland. 137

formation (principally chalk and basalt) occur towards the summits
of the hills, capping the primitive rock.

The valley of Glendun is formed exclusively of mica slate as
far as Done, a village more than five miles inland, here the secon-
dary deposits commence, at the elevation of 590 feet above the sea.

From the mouth of the Glendun river the mica slate extends
along the coast, in a northerly direction, as far Murlock Bay, near
Fairhead, a distance of about seven English miles: it is here asso-
ciated with a few other primitive rocks, hereafter to be described.
The local name of Cushleak is given to this part of the coast.

Vestiges of mica slate occur on the road from Cushendon to Bally-
castle. J have seen it in situ at Ballyvarleys in the bed of a rivulet,
skirting the base of Knocklead on the north-east, and have traced it
in several other points on the slope of that mountain, particularly at
Kileseg, and the low Market hill near Ballycastle. Passing
into the county of Londonderry, that great and central mass
of mica slate, which from the parallel of the Mayowla river reaches
Lough Foyle, extending to the east and west between the Roe and ~
the Moyle, claims our principal attention ; it may be computed to
cover a surface of at least 476 square English miles of mountainous
ground, over which several distinct summits are scattered, including
the following, of which I have determined the elevation :—Sawell
2257; Feen Glen 2097; Mullaghash 1677; Moneynieny 1477 ;
Sphell Covagh 1867; and Dunlogan mountain 1467,

The river Roe, from the neighbourhood of Newtown Limavaddy
to its source, may be assigned as the general line of demarcation
between this primitive group and the red sandstone which forms
the base of the secondary mountains of the third system, (see In-
troduction): the mica slate is however occasionally seen on both

WOLS lve s

138 Dr. BERGER on the Geological Features

sides -of the channel of the Roe, as is the case at the romantic
waterfall called the Dogsleap, near Newton, where a fine natural
section of that rock is displayed, and lower down the river in the deer
park of Mr. M‘Causland ; from the district of Tamna Arran near the
head of the valley of the Roe, the boundary passes along the Douglas
river, a branch of the Mayowla to its confluence: thence it sweeps
to the east of the Cairns of Slieve Gallion, and near the confines of
Moneymore and Lissane, towards the sources of the Ballinderry
river, in the north-east of Tyrone.

A little to the north-east of the source of the Roe, and almost
surrounded by the secondary and basaltic ridges of Benbradagh and
Cragnashoack, we are surprized at meeting with a small insulated
district of mica slate; it forms the entire mass of the mountain of
Coolcoscrahan, which rises nearly 1300 feet above the level of the
sea.

The characters of the mica slate vary much less than might be
expected, considering the extent it occupies in the north of Ire-
land ; upwards of two-thirds of it belong to the talcky variety,
the remainder to the common, or that which contains the least
quantity of mica and the greatest of quartz.

A circumstance rather remarkable is, that, amongst the multi- |
plicity of specimens I have examined, I do not remember one that
contained garnets. How far that extensive formation of mica slate
may be metalliferous, it is impossible to say in a country hitherto so
little explored. |

The subordinate rocks which not unfrequently occur in the mica
slate, shall be noticed separately.

of the North of Ireland. 139

C. Lrimitive Limestone.

Primitive limestone exists in several parts of the counties of
Antrim and of Londonderry as a subordinate member of the mica
slate formation with which it sometimes alternates.

Granular and blue micaceous limestone, with veins of coloured
spar, quartz, and green chlorite, occurs on the north-west side of
Cairntogher, in the county of Londonderry, at the height of about
800 feet above the level of the sea.

The same granular and micaceous limestone exists in Bennady
Glen, and at the old church near Dungiven, at the latter place
in large lamellar concretions, passing into compact with a greenish-
grey colour: at Banagher church it occurs blue, micaceous, and
in small granular concretions. Near Clady, on the road from
Dungiven to Londonderry, it is extremely talcky with some
quartz nodules; and in the deer park of Mr. M‘Causland, near
Newtown Limavaddy, it possesses the same character, containing
some thin layers of quartz and a few iron pyrites.

Lastly, on the north-east side of Slieve Gallion, there is a pri-
mitive limestone which contains crystallized hornblende in abun-
dance: it breaks spontaneously into large rhomboids, incrusted
over the natural joints with calcareous spar, of a green-yellowish
colour. .

At the point of Taur in Antrim, the colour of the limestone
varies from grey to reddish grey, and greenish grey ; the concretions
are rather large, and the texture passes sometimes from granular
into compact ; it contains only a small quantity of magnetic iron

pyrites.
s 2

140 Dr. BERGER on the Geological Features

The strata are alternately coarsely and finely slaty: the thick-
ness of the whole mass may be rated at fifty feet. Veins of
calcareous spar intervene as seams between the individual strata.

At Toberbilly, on the north-west side of Knocklead, near
Ballycastle, at an elevation of four hundred and ninety-four feet
above the level of the sea, I traced a bed of granular and micaceous
limestone through a considerable extent towards the town-land of

Cloughamany.
The concretions are rather small, and there are linings of talc

along the seams of stratification.

D. Primitive Trap.

The remark of Werner, that primitive trap contains no iron
clay, but is wholly or almost entirely composed of hornblende,
appears to be extremely appropriate, and to draw an excellent line
of demarcation between primitive and the secondary trap.

1. a. Common Hornblende Rock.

More than two-thirds of the Foy mountain, near Carlingford,
are composed of a succession of stairs formed of primitive trap.
Proceeding from the bottom towards the summit of that moun-

.

of the North of Ireland. 141

tain, which is 1850 feet high, the trap is seen passing from an
homogeneous to a porphyritic texture. The latter imparted by .
lamellar crystals of felspar of a white colour, and of rather con-
siderable size: gradually the accidental ingredient becomes the
essential one; the colour of the felspar becomes greenish, and in that
state the rock approaches more nearly perhaps to the character of
sienite than to that of trap.

In its genuine state, in the lower part of the mountain, the rock
puts on the usual coated appearance which originates from decay.

On the eastern slope of Slieve Birna, one of the Mourne moun-
tains, at one half nearly of its height, I observed a bed of hornblende
rock, apparently interposed in the granite.

At Slieve Anisky, a hamlet on the road from Castlewellan to
Dromore, I noticed another bed of hornblende rock, but I am doubt-
ful whether it belongs to this class or to that of transition,

b. Hornblende slate.

This subordinate member of the primitive trap series frequently
occurs, forming distinct beds, in the mica slate of Antrim and Lon-
donderry.

In the former county it is found in the valley of Glendun, and
along the coast from Cushendun to Tor-point.

In the latter it occurs in Bennady-glen, in Aglish-glen, and in
the bed of the Roe river near Dungiven. The bed of hornblende-
slate in the latter place occupies an extent not less than four hun-
* dred yards, ending by the old church, where it runs parallel to a

142 Dr. Bercer on the Geological Features

bed of primitive limestone, before mentioned. It has there a ten-
dency to hornblende rock, while in Bennady-glen it displays a
granular texture and a few plates of mica.

2. Greenstone.

I have found greenstone in Ravensdale park, at the foot of the
mountain of that name, and on the west side of the Faughel hills.
I suspect that in those two instances, the latter particularly, it forms
beds in the newest granite.

3. Greenstone slate

rests against the acclivities of the Mourne mountain, but the strata
never rise very high, seldom exceeding 5 or 600 feet ; one instance
only was observed of a hill exclusively formed of this rock, and
that did not attain a greater elevation than about 800 feet.
Attempts have been made to quarry it for roofing slate, and
were the works conducted with spirit they might perhaps supply
{reland with as good slate as that now imported from Wales, which
appears to belong to the same formation.
The greenstone slate of the Mourne mountains contains ap-
parently no crystallized hornblende in the basis, though it is dis-
seminated through the latter, as is shewn by the manner in which
it fuses before the blowpipe. I have remarked in it some crystals

of the North of Ireland, 143.

of glassy actynolite passing into hornblende, veins of quartz, mag-
netic and common iron pyrites. ‘The basis sometimes approaches in

its nature to clay-slate.
4, Hornblende with Mica.

This aggregate rock composes the top of Clark’s hill or Slieve-
sleet, five hundred and forty-eight feet above Castlewellan. I also
noticed it on Slieve Croob, between Slieve Nasky and Bakaderry
town. I saw it again in loose blocks about Castlewellan.

A. Druidical monument at Coagh near Cookstown, is partly
made of an aggregate of crystals of hornblende. The same com-
pound I observed, but not in sztw, at the basis of the mountain of

Coolcoserahan. -

E. Porphyry.*

Felspar porphyry occurs in the county of Down, in the bed of the
Finish, on the north-west side of Slieve Croob, near Drummara in
the lower Iveagh; and in a decomposing state at Ballyroany, four
or five English miles north-east of Rathfriland. In the first of these
localities it is interposed in a compound rock of granular quartz

and mica.

* See the article on some porphyries of doubtful formation at the end of these extracts.

144 Dr. Bereex on the Geological Features

In the mica slate district of Antrim, several beds of felspar por-
phyry are found; they may be traced along the coast from Tor-
point to Cushendon, and thence inland along the old road to
Ballycastle.

In Londonderry, the fundamental rock on the east side of Slieve
Gallion is a variety of felspar porphyry strongly resembling sienite,
with which rock it probably alternates in this mountain. :

In the same neighbourhood felspar porphyry may be traced with-
out interruption from the top of the glen of Latterane to the bed of
the Knockadoo river on the road from Lissane to Moneymore.

F. Svenite.

I have traced this rock in the low country adjoining the town
of Newry for three or four miles on the road to Dundalk, for the
same space on that to Armagh, and towards Bainbridge as far
nearly as the four mile house. It is perhaps more extensive.

The sienite is unstratified, cropping out in independent mases,
but rent into pieces mostly of a rhombic figure, the natural ‘joints
of which are generally rusty.

It is finely granular, composed of felspar of a blood red, flesh
red, or greyish colour, with some quartz, hornblende, and black
mica, besides two ingredients, accidental but not uncommon,
namely, iron pyrites and small garnets.

The sienite that crowns the summit of Foy mountain near Car-
lingford, contains only a few broad plates of black mica, with
greenish felspar and hornblende in large concretions.

of the North of Ireland. 145

Slieve Croob in the lower Iveagh, the most conspicuous hill of a
small group that lies nine miles in advance to the north of the
Mourne mountains, seems formed on its north-east and south-east
sides of different varieties of sienite, some of which are porphyritic
and very beautiful: the crystals of hornblende are extremely well
defined, and the compact felspar constituting the basis has a
brownish or smoky colour.

This sienite crops out at intervals from Bakaderry town to the
top of Slieve Croob, occupying an elevation of about 900 feet.

Slieve Gallion, in Derry, exhibits sienite in connection with por-
phyry, and either of a porphyritic texture or in large concretions ;
{ met with an elegant variety on the road from Lissane to Lough
Finea; the felspar is either slightly green or flesh-red with horn-
blende, quartz, and some pyrites. This rock acts strongly on the
magnet.

_In the bed of the Black-water near the valley of the Mayowla, on
the north-west side of Slieve Gallion, the sienite is mostly composed
of crystallized hornblende with some felspar and iron pyrites, verging

therefore into greenstone.

VoL. Ut Gh

146 Dr. BERGER on the Geological Features

Il, TRANSITION ROCKs. *

. Greywacke.

. Transition limestone.
Transition trap.

- Old red sandstone.

Om p

A. Greywacke and Greywacke Slate

occupies a great part of the baronies of Ardes, Castlereagh, and the
two Iveaghs in the north of the county of- Down, whence they
extend through Armagh and Monaghan into Cavan. The accom-
panying map (Pl. 8.) will convey a sufficiently accurate idea of
their extent. Their characters do not differ from those which
they exhibit in other countries already frequently described.

The greywacke slate is worked extensively for roofing slate at
Ballyalwood in the center of the peninsula of Ardes: a variety
however, still better adapted to this purpose, remains yet neglected
at Cairn Garva, on the west-south-west of Conbigg hill.

At Cultra, on the north-east of Belfast lough, flinty slate and
drawing slate occur as subordinate formations in the greywacke.

Lead and copper ores have been found in this formation at
Conbigg hill, between Newtown Ards, and Bangor, and I believe
at some other places. A mine was formerly worked at Conbigg,
but is now abandoned.

* The term transition is here employed merely as the name of a class of rocks inter-
vening in their position and intermediate in their character between the primitive and
secondary classes, no other or hypothetical meaning is attached to it. The old red sand-
stone here described, has been associated with these rather than with the secondary rocks,
because it appears in one instance at least to alternate with greywacke.

of the North of Ireland. 147

B. Transition Limestone.

The entrance of the noble bay of Carlingford is bounded on the
south-west side by an obtuse point of land very low, and almost on
a dead level, whence the Foy mountain boldly rises, falling away
to the south towards Cooley, where it forms the ridge named
Golding mountain.

The greater part of this flat point of land, ending on the north at
Carlingford Castle, is occupied by a limestone formation which I am
disposed to refer to that of transition. |

It covers a square surface of about nine English miles, reappearing
at the Block-house island in the middle of the bay, but I am not
aware that there are any vestiges of it on the shore in the county of
Down, which limits the north-east side of the bay.

The strata lean on the east side of the Golding mountain dipping
to the south east: they however rise to a very inconsiderable
height upon its abrupt declivity.

There are quarries opened in a continual line to the extent nearly
of one English mile, at the foot of the Golding mountain, the depth
of the quarries varying from fifty to eighty feet: limestone is raised
besides in other places nearer to the shore, at Cooley, Mullaghtre,
and the Gan rocks.

This limestone is remarkable, because it alternates both with
transition trap and with greywacke slate; evidently so with the
former at Cooley, and with the latter at the Gan rocks.

The solid strata are frequently traversed by veins and thin layers
of calcareous spar: between them intervene many thinner beds

passing into slaty marl.
T 3

148 Dr. BERGER on the Geological Features

The limestone itself somewhat varies in its characters at the
different places where it occurs. In point of colour it passes from
bluish-black to smoke-grey: the first variety is more compact, the
lamellar concretions less evident, and it is sometimes traversed by
veins of flinty slate; small quartz concretions are occasionally though
rarely interspersed in it. I have seen in it crystallized iron pyrites :
it contains superficial impressions of cornua ammonis, covered with
iron pyrites; madrepores, both ramose and columnar; nautili figured
by Walcott, (Bath fossils fig. 44.)

Two small limestone districts occur near the shores of Strangford
Lough, one at Lisbawn near Down Patrick on the south-west, and
the other near Cumber on the north-west; the latter appears to
be of the magnesian variety ; orthoceratites have been noticed in it.

It has not been ascertained to what formation these limestones
belong, but since they occur in a district where greywacke prevails,
they may with greater propriety be noticed here than under any

other article.

C. Transition Trap.

The formation of greenstone which alternates with the limestone
at Carlingford has invariably a crystalline texture, but differs in its
other characters in presenting the following varieties.

1. Common greenstone.

2. Close grained and porphyritic.

3. Approaching to greystone.

The beds are three or four feet thick.

of the North of Ireland. 149

On the east side of Slieve Gallion at the head of a narrow glen
called Tinteagh Glen, about 1300 feet above the level of the-sea,
crop out several unconnected masses of greenstone.

They are totally unconnected with the flat stratified trap which
overlies the chalk, and crowns the summit of the mountain. The
fissures are lined with calcareous spar, and veins of crystallized heavy
spar and of red compact iron stone are contained in this rock,

D. Old Red Sandstone.

This formation has been observed only in the two following
districts, and even there its extent appeared to be very limited.

1. In the county of Down, on the sides of Strangford lough.

2. On the N.E. coast of Antrim, between the bays of Cushendall
and Cushendon ; and again in Murloch bay.

Vestiges indicative of the old sandstone may also be traced along
part of the shore of the Isle of Rathlin opposite Fairhead.

The tract of sandstone first specified extends from the E.N.E,
side of Strangford lough to Scabro hill on the opposite side of
that lough, appearing likewise at Ballymasca, Dunlady, and Kirk-
donnel,

Scabro hill rises 483 feet above Strangford lough, its summit is
composed of a cap of greenstone about 150 feet in thickness; the
remaining 330 consist principally of the sandstone, which may be
observed in one* of the quarries opened on that hill (to procure this
material for architectural purposes) in distinct beds of very variable
thickness alternating with greywacke.

* The name of this quarry is the White quarry

150 Dr. BercER on the Geological Features

The colour of this sandstone is reddish or greyish; its texture is
either conglomerate, including fragments of greywacke slate, or
finely granular, composed of quartzose grains imbedded in a cement,
sometimes calcareous and sometimes siliceous. The greenstone
which caps this hill differs very slightly from that associated with
the floetz trap. .

Lord Londonderry has caused this formation to be bored to the
depth of 500 feet in the fruitless search for coal on the east side of
Strangford lough near Mount Stewart; if to this depth the height
of the sandstone on Scabro hill be added, it will give from 800 to
900 feet as the known thickness of this formation. The greatest
length of this district of sandstone does not exceed six or seven
English miles. It appears to rest upon greywacke.* .

The tract of this formation between the bays of Cushendall and
Cushendon, is yet more limited than the preceding. On the coast
it occupies a line of between three and four English miles, and
extends about the same distance in an inland direction. The
highest point of the cliffs on the coast in this range is only 124
feet; but the hill of which they form the escarpment rises at
Jeaveragh near Cushendall church to the height of 522 feet : this
is the greatest elevation which the sandstone of this district attains.

The strata dip into the sea towards the E.S.E. under an angle of
about 32°. In the bay of Cushendon several caverns of considerable
magnitude occur in this rock.

The general character of this formation is that of a conglomerate ;
it passes however into a coarsely granular texture, and in one place
(the Red bay of Cushendall) into a finely granular: its colours
vary from red to grey. !

* The arrangement of the sandstone formations in the north-east counties of Ireland,
forms the most difficult problem presented by their geological relations. The sandstone

of the North of Ireland. 151

The conglomerate contains in great abundance large pebbles of
quartz, and more rarely of hornstone porphyry; also of a rock
which appears. to. have been a greenstone porphyry, but is much .
altered by decay; and lastly of mica slate. The coarsely granular
variety consists of quartzose concretions imbedded in an argillo-

calcareous cement.

/This sandstone formation appears to rest on the mica slate
which succeeds it on the north side of Cushendon bay, and occu-
pies the district of Cushleak described in a former article. At the
opposite or N.W. extremity of that district we may again trace the
sandstone in Murloch bay: it there appears very distinctly on the
beach near the great Whin dyke, in its conglomerate form.

To the westward of Church bay in the Isle of Rathlin, and near
a spot called the Black rock, I found fragments of the old sandstone
associated with blocks of syenite in such abundance as to impress
me with a strong belief of the former existence of both these rocks

of Lough Strangford with its cap of greenstone presents so obvious an analogy to the
structure of Cragnashoack at the southern extremity of the floetz trap chain in London-
derry, that we might be almost tempted to infer the identity of the sandstone in
both instances, and, since that of Cragnashoack is certainly the newer variety, to
question the propriety of assigning to that of Scabro hill the antiquity which has been
claimed for it in the text: its apparent connection with the sandstone of Belfast lough,
also seems to favor the idea of its belonging to the newer variety, for in travelling between
Belfast and Newtown Ards, the road is said net to exhibit any rock but sandstone, in situ,
although hills of greywacke rise within a small distance on either side: yet the fact
mentioned by Dr. Berger of the alternation of this sandstone with greywacke, seems
decisive as to its age.

The sandstone of Cushendon also appears to require further examination: one of the
most interesting facts concerning it appears to have escaped Dr. Berger’s notice, namely,
its connection with a formation of reddish clay porphyry. The observations made by
Mr. Buckland and myself on this formation will be found in the account of the sections
presented by the coast, appended to these extracts. It is only mentioned at present as
fording an analogy between the sandstone which skirts the mica slate of Cushleak, and

occurs in a similar situation in the island of Arran.

152 Dr. BERGER on the Geological Features

in that direction. Were the sea to retire a few fathoms and
disclose the foundations of Rathlin, we should very probably
discover the trap which constitutes the present surface of that island,
resting on the old sandstone; and that rock in its turn reposing

upon syenite.

III. FLOETZ ROCKS.

A. Limestone underlying the Coal formation.
B. Coal formations.

C. Sandstone formations.

De Litas:

FE. Green Sandstone or Mulattoe.

F. Chalk.

A. Limestone* underlying or associated with the Coal Formation.

At the entrance of Cookstown on the road from Coagh, there
are quarries of a shell limestone formation supposed to extend
itself to the south as far as to Steward’s town, and nearly for one
mile in the other directions: it is disposed in strata alternately

* The limestone here described appears to constitute a portion of that great limestone
formation which may be traced through the counties of Kilkenny, Kildare, Dublin, the
Meaths, Roscommon, the south-east of Mayo, Sligo and Fermanagh. The great coal
districts of Kilkenny in the south, and of Lough Allen in the north, repose upon it; as
aso do those of Dungannon and Coal Island described in the next article.

The points described in the text are principally situated on the north-west of the coal
formations last mentioned, and near the line separating the sandstone associated with the
coal, from the primitive mountains connected with the great chain of Londonderry.

of the North of Ireland. 153

solid and compact, earthy and marly which vary from one to
three feet in thickness, and dip north-west at an angle of about
27°, The texture of this limestone is compact, though composed.
of distinct lamellar concretions: it is traversed by veins of calc spar
of a reddish colour, and is soluble in acids without residuum: the
specific gravity is 2.84. It is used for building; and the mortar
made from it is said to be considerably stronger than that of the
newer white limestone. It contains organic remains.

At Desartmartin in the county of Derry, ten miles to the north
by east of Cookstown, there is a similar shell limestone of a smoke
grey colour, which is also quarried. ‘The strata dip north west at
an angle of eight degrees. ‘They contain two sorts of terebratulites,
namely, terebratula gigantea and terebratula producta, and imbedded
nodules of a glassy quartz sometimes of the size of an hazel nut,
a circumstance that renders the blasting of this limestone with
gunpowder attended with danger. I was informed that at the
depth of seven yards, the bed of limestone is exhausted and reposes
on a stratum of clay, but I had no opportunity of ascertaining
the fact myself.

On the south of these coal districts the limestone is yet more extensively displayed,
intervening between them and the northern boundary of the greywacke district in Armagh :
it is here exhibited skirting the banks of the river Blackwater above Charlemont for
several miles ; and the country on the south and south-east between Charlemont, Loughgall,
Kilmore and Armagh, is principally occupied by this limestone. On the east of this
district near Hillsborough and Lisburn, it seems probable that the sandstone and grey-
wacke come into contact, the limestone being wanting: but still farther in the same
direction, at Cultra and Holywood, on the southern shore near the middle of Belfast
Lough, the limestone again appears in a position intermediate between the sandstone and
greywacke, but probably not in immediate contact with the latter, a red sandstone of
older formation being said to occur in the interval. This limestone is of the magnesian
variety, (which also occurs in the same formation near Dublin) its texture compact, but
not crystalline, its fracture granular, its colour ochre yellow; it contains cavities lined
with calc spar, and presents organic remains: the thickness of the beds varies from one to
six feet.

VoL. Ill. uU

154 Dr. BERGER on the Geological Features

The shell limestone of Desartmartin re-appears two miles farther
to the north-east at Dromore, the strata preserving the same dip,
direction and characters: the quarries of Dromore are more exten-
sive than those of Desartmartin.

At Gore Tarminey in the parish of Kilcrouaghan not far from
Dromore, the shell limestone shows itself again, but under the
character of swinestone: it is variegated, and contains terebratula
gigantea. ‘The strata dip at an angle of 12>, |

At the coal works of Ballycastle two English miles north of
the town, strata of shell limestone are to be seen on the shore,
and may be traced at low water running out to sea in their line
of bearing, which is N.E. 17°. they dip therefore to S.E. 73°.

The strata are alternately solid and marly, the former constituting
beds of three or four feet in thickness, the latter not exceeding half
a foot. The solid strata are of a compact limestone with lamellar
and rhombic concretions, the colour smoke grey.

I have examined several specimens of a variety of this limestone
containing ramose madrepores, said to have been found on the west
side of Lough Neagh in Tyrone.

B. Coal Formations.

I have to notice four partial coal formations: they occur in the
following counties.
I. Tyrone: at Coal-island and Dungannon.
If, Antrim: near Ballycastle.

1. Two Coal fields, as coal formations are usually styled in
England, exist in the county of Tyrone, at no great distance the

of the North of Ireland. ~ 155

one from the other, viz. at Coal island and Dungannon ; with the
latter I am totally unacquainted: it is I believe, by far the most
extensive of the two: whether they may be considered as connected
and thus constituting but one single formation, I do not pretend
to say.

The coal formation of Coal island is in an open part of the
country, though with a gently waved surface. The whole extent
of the coal district or Pound, as it is called, does not exceed as
I was informed, four hundred yards square.

The works in this district appear to have been prosecuted
formerly with more activity than at the present period, some of
the pits being now abandoned ; several however still remain, but
they seem to be conducted with little of capital or of spirit. The
steam engine has not yet been introduced; the power of horses
only is employed to raise both coals and water, which last is
unfortunately very abundant. In one pit called the Mary Anne,
which I visited, 150 barrels were computed to be drawn out every
day. None of the pits (so far as I was informed) exceed 75 yards
in depth: the quantity of coals raised daily in the Mary Ann pit
amounted to thirteen tons, though no more than thirty colliers
were employed. The coals are said not to cake, they. are appli-
cable to all domestic purposes, and are I believe mostly consumed
by the inhabitants of the adjacent part of the country, notwith-
standing a bounty allowed by government to send them either to
Newry, Belfast, or Dublin.

Several seams of coal occur, the main bed is nearly six feet in
thickness; its general direction is north-west and south-east: the
dip of the strata is here towards south-west. At Dungannon, as
I was informed, this direction becomes reversed.

u 2

156 Dr. BERGER on the Geological Features

2. The collieries of Ballycastle occupy an extent of less than one
English mile along the coast. They have been long wrought, and
were once in a more flourishing state than they are now: they
formerly used to send from ten to fifteen thousand tons of coal to
the market yearly, whereas the ground bailiff with whom I con-
versed several times, assured me that the quantity now exported
did not amount to more than fifteen hundred or two thousand tons.

Owing to prejudice, I believe, rather than to greater expence,
the country people prefer burning turf rather than coals, and even
the inhabitants of the Isle of Rathlin, who have but a very spare
quantity of that combustible, come to the Main to carry it
over instead of coals, though ultimately it must be more expensive
and surely more troublesome.

The Ballycastle coals are therefore sent to Dublin, chiefly on
board the numerous trading vessels bound to that port from
Londonderry, which thus instead of going thither in ballast,
take a freight of coal on their passage. The Irish coals in Dublin
receive a bounty equal to the duty laid upon the English coals.

There are but four coal works now wrought out of twelve
which were formerly opened near Ballycastle: Gob colliery is the
most extensive and advantageous.

As the beds of coal crop out a few feet above the level of the
sea, there is no occasion for sinking shafts, but some of the
horizontal galleries are of great extent; that of Gob colliery into
which I went, is not less than eight hundred and twenty yards:
they have a considerable quantity of water, and, which is worse,
they suffer so much from foul air that the colliers cannot stay
more than eight hours out of twenty-four in the mine. The beds
dip to the south-east about one foot in nine.

I should apprehend that this partial and broken formation is

mostly exhausted.

of the North of Ireland. 157

It may not be improper to subjoin here the series of the rock-
measures at two or three of the collieries which I visited in the
north of Ireland. JI shall first give the provincial names, adding
the scientific terms which appear to correspond to them.

ROCK-MEASURES OF THE MARY ANN PIT,
IN THE COUNTY OF TYRONE,

Jrom the surface downwards.

PROVINCIAL TERMS. GEOGNOSTIC NAMES. FEET. |INCHES.
ly Wandstohe;saas; . lasiado -oskt-sosmvso -aglds3 33
2 bY Bite-metal, 55 «1m 0.4 Grey-white clay Ironstone | 4
SP IUSUEECR c Non Meltaees oe oot SPAteRClAY stems tats isp Bs 2
4 |Craw-coal ......... MBlateseoale. LE. Awe. 1 6
Se eee. Sher oe as Safe siatewclay’ | f° tc. are 3
6 |Grey-metal .......... Reddish brown clay iron-st.| 21
(RS ay ree MRO os o's ois. ao cua 3 « 1 6
B jeBoneseoalos 944 03 veow, bie. Abad odio luo aninl: 2 4
9 {Turbage (i... as above! ws 8. UTR 22 4
10 {Grey Bind ..... MOTT ote Le hehe oth eee 9
11 |Black-measure........ WESTIE Pes o's vars fa cars 0k 9
[EOE EE COUT one oe ey ae eae na ane ee ae 6
TSS eS ee eee Dlatemaelay 1. 4.04.0 oe d5ne,05 2
1444 Main Seam,of Coal.oo:<s foyer gsrasiderme 10 Ghasie mere’ 5 to 6
Total - - 104 A

This account of rock-measures falls short of the depth of the pit
itself, by seventy six feet; and we must either suppose that some of
them recur once or twice more in the series, or rather that it is not
perfectly correct: my authorities in this and the following table
were the miners who attended me as guides.

158 Dr. BERGER on the Geological Features

ROCK-MEASURES OF LUGG-GLASS* (The Green-Hollow. )
COLLIERY AT BALLY-CASTLE IN THE COUNTY OF ANTRIM,

Jrom below upwards.

PROVINCIAL TERMS. GEOGNOSTIC NAMES. FEET. |INCHES

HAM A Sandstone. .........--..
«(Nes "sleep ie napadaye Slate-clay fo. Steeles
siejtstaiei etal erate Sandstone, probably
Dares NS sei Main bed of Slate-clay
RaAtot eee DUES (0081 5 a's. 6.0 os c's

eee ee ewe ewe eo eee © | AAUUN eg eee tere nrereeeeneee

Total - - 124

The preceding tables evince the general resemblance which the
members of these coal formations bear to those of other countries.
It is necessary to add very few remarks.

The coal of these districts is almost entirely slate coal; it may
perhaps be suggested as a general observation concerning the Irish

* The above section relates only tothe beds contiguous to the coal now worked. Sections
of the entire cliff have been given by Mr. Whitehurst in his Theory of the Earth, page 260,
and by Mr. Dubordieu in the Statistical Survey of Antrim; but it is impossible to reconcile
the one to the other. From the hasty survey which I was myself able to take of this
spot, I can only furnish the following particulars :— .

The total height of Cross Hill, in the north face of which the collieries are worked, is
about 500 feet, of this elevation about 150 feet is formed by a cap of columnar green-stone,
which reposes on alternating strata of sandstone and slate-clay, these extend about 150 feet
in depth, and cover the bed of coal in which the workings are situated, and which occurs at
an elevation of about 200 feet above the beach; below it are other strata of slate-clay, with
perhaps some seams of imperfect coal and sandstone, and we particularly observed beds of
the latter rock, of an intensely red colour and of enormous thickness: lastly, strata
of limestone are seen emerging from the sea towards the west of the collieries ; the interval
between the coal and the limestone is much concealed by slopes of debris, covered with an
imperfect vegetation, which rest against the base of the cliff.

An opinion is prevalent among some of the miners, thata thicker stratum of coal than that
at present in working would be found by driving adits beneath the level of the sea.

of the North of Ireland. 159

coal formations, that supposing a line drawn across the Island in
the parallel of Lough Allen from east to west, the coal found to
the north of that line is principally slate-coal, and that on the south
cannel coal. In one of the works, however, in Coal Island, a bed
of cannel coal six feet thick is said to have been wrought.

The slate clay at Mary Ann Pit contains impressions of aquatic
plants, vegetable impressions similar to those of the Derbyshire
collieries have also been observed in the Ballycastle district.

Clay ironstone occurs both in nodules and beds, and brown spar
passing into sparry iron ore has been observed at the coal works of
Ballycastle, where it forms a bed of some thickness traversing the
cliff at a little depth below the principal seam of coal.

A bed of trap lying in a conformable position between the
strata of sand, occurs a little to the eastward of the coal works of
Ballycastle, between Fairhead and the little Glen of Port-na-crea,
along the Crag of Sron Gal or of the “* White-nose.”

This geognostic fact, the only one of the kind I have seen or
heard of in the north of Ireland, was pointed out to me by the
ground bailiff of the collieries, who called it a horizontal dyke.

Its thickness is about two feet. It has a slaty structure, and is
micaceous where it lies immediately in contact with the sandstone,
the usual characters of which appear altogether unaltered. . It breaks
spontaneously into forms resembling triangular pyramids ; the tex-
ture is remarkably close, it is almost entirely formed of finely
crystallized hornblende, with some thin scaly parts of white felspar :
it acts on the magnet, and yields a black enamel before the
blowpipe.

* Several vertical dykes also occur traversing the coal measures near Ballycastle, these
asill be particularly described ia the account of sections on the coast.

160 Dr. BERGER on the Geological Features

C. Sandstone Formations.

On the skirts of that elevated district in the county of Antrim
and in the eastern division of Londonderry, which is occupied by the
more recent floetz rocks (namely lias, green sand and chalk, sur-
mounted by a vast cap of basalt) extensive deposits of sandstone
occur, forming the basis on which this lofty platform appears to
repose.

These deposits of sandstone appear therefore to be in every in-
stance of greater antiquity than the lias which they support, they
seem also to be partly coeval with and partly more recent than the
formations already described, as they are seen either alternating with
or overlying the members of those formations where they can be
traced in connexion with them.

They may be considered as identified partly with the coal sand-
stones of England, and partly with the formation here known by
the name of red rock marle, the lower beds of these deposits being
referable to the former class of rocks and the higher which contain
gypsum to the latter; to ascertain however the precise demarcation
of these subdivisions is a task for which materials are as yet
wanting.

A further difficulty occurs in two instances, namely, at Cushen-
dall bay and at Murloch bay, where these deposits are brought ap-
parently into contact with the old red sandstone, without the inter-
vention of the coal measures or their associated limestone, so that it
is hardly possible to assign the points at which the old sandstone ter-
minates, and is succeeded by these younger members of the same
family.

The sandstones intended to be described in the following article,

occupy the following localities.

of the North of Ireland. 161

1. The valley of the river Lagan from Moira to Belfast, and the
north-west shore of Belfast Lough as far as the Peninsula of Magee.

2. Several points on the north-east coast of Antrim.

3. A line in the eastern division of Derry and north east of
Tyrone, extending from the mouth of the river Roe to the south
west extremity of Lough Neagh.

1. Sandstone of the valley of the Lagan and Belfast Lough.*

The sandstone formation may be traced from the south west ex-
tremity of the county of Antrim, where it joins that of Down,
occurring between Moira and Lisburn, at Maheramesk, Spencer’s
bridge and Maheragall ; it proceeds along the valley of the Lagan,
extending into that of the Forth, a small river which becomes tribu-
tary to the Lagan near Belfast ; from that town it occupies the
road to Carrickfergus, whence it ascends the valley of the Wood-
burn, another brook discharging itself into Belfast Lough; it
afterwards extends as far as Castle Chichester, in the island of
Magee.

The prevailing colours of this sandstone are various shades of
red and reddish brown, but it is variegated by many coloured
stripes ; it contains clay-galls ; its texture is friable ; the cement is
calcareous ; spangles of mica constantly occur.

At Carrickfergus, where the rock is more than usually adherent,
it is raised for flags.

The upper members of this formation become argillaceous, con-
sisting of beds of reddish brown marle, alternating with a greenish
slaty marle, and an indurated grey calcareous marle; these may be

* On the opposite side of Belfast Lough this sandstone extends towards Holwood,
where it rests upon the limestone before described, and we traced it for some distance on
the road from Belfast to Newton onwards.

VoL. Hl. x

162 Dr. BERGER on the Geological Features

seen at Maheramesk near Moira, in the valley of the Forth near Bel-
fast, in the valley of the Woodburn, near Carrickfergus, and at Castle
Chichester in the island of Magee. In all these localities, veins of a
delicately white fibrous gypsum occur: salt springs, the usual ac-
companiment of similar strata, are found near Carrickfergus, and in
other places.

The sandstone has been sunk into near Lisburn nearly 200 feet
without reaching its inferior extremity, and the red marl which
overlies it near Belfast is estimated as varying from 40 to 100 feet
in thickness.

The outgoings of the sandstone strata are low, they dip towards
the hills on the north west.

2. Sandstone on the east and north east coast of Antrim.

The same sandstone which has thus been traced as far as the head
of Larne Lough, may thence be pursued in various points on this
coast, but since its superior edge is often depressed below the level
of the sea, and on the other hand its inferior edge is in one instance
elevated far above that level resigning the coast to formations of
greater antiquity, it presents in this part of its course an irregular
and broken line, of which the description will be the more readily
followed if postponed to the explanatory notes on the section of |
that part of the coast subjoined to this paper.

3. Sandstone in the east of Derry.

The variegated marle which covers the sandstone, first makes its
appearance, rising from the level of the sea, a little to the west of
Downhill near the mouth of the Roe, thence it passes to the south
west, bassetting along the base of the bold headland of Macgilligan,
and of Benyavenagh the most northerly mountain of the secondary
chain in Londonderry. At Kedy hill the next of the groupe, the
sandstone, which continues ascending towards the south west,

of the North of Ireland. 163

attains the elevation of 450 feet above the sea; in the adjoin-
ing mountain called Donald’s hill, its upper limit rises to 900
feet ; it occupies nearly the same level in Benbradagh, and at Crag-
nashoack the southern point of the chain gains its greatest height,
being there 1589 feet above the sea. In this mountain the sand-
stone and basalt are in contact, the chalk being deficient. Cragnash-
oack and Fairhead are, it is believed, the only instances in this dis-

trict where the trap is seen decidedly reposing on any other
rock than the chalk.

The sandstone of Benyavenagh, of Kedy and of Donald hill, is red,
slightly variegated with yellowish stripes of a rather loose texture ;
it has a calcareous cement, and contains specks of mica.

The sandstone of Benbradagh has the character of sandstone slate,
the texture coarsely granular ; colour greenish white ; with a calcare-
ous cement, and containing spangles of mica. It extends to Dungiven,
and probably reposes on the mica slate, which occupies the left
bank of the Roe; its thickness in this hill cannot be less than
five hundred feet. About a quarter of a mile from Dungiven,
at the opening of Benady glen a sandstone conglomerate occurs,
probably connected with this formation.

The insulated primitive district of Coolcroscrahan, which is
situated. behind Benbradagh on the north east, appease to be en-
circled with a ring of sandstone and marle.

In Cragnashoack, two varieties of sandstone may be traced, the
upper beds consisting of a coarse grey sandstone with a calca-
reous cement, while the lower strata are more distinctly slaty and
micaceous, and have a yellowish colour and a siliceous cement.

From Cragnashoack the sandstone extends to the south, abutting on
the north east slope of Slieve Gallion. Near this point it appears to

repose upon the shell limestone of Desert Martin, ranging from
x 2

164 Dr. BERGER on the Geological Features

thence by Moneymore towards Lissane; on the Canesee river, asmall
brook which is crossed in passing between the two last mentioned
villages, strata of sandstone conglomerate are found.

Near Cookstown, grey sandstone passing into white occurs on
the road to Dungannon, it extends beyond the bridge over the
Blackwater river, the outgoings of the strata rise south-west
43° under an angle of 8°. There are other sandstone quarries one
mile and a half from Cookstown towards Moneymoré ; a red variety
is here found, it is finely granular, with a calcareous cement, the
strata crop out south-west 53°, at an angle which varies from 13°
to 25° as they increase in depth.

At Coal island, in the county of Tyrone, sandstone constitutes
the superficial stratum, two varieties may there be distinguished, both
however agreeing in having a siliceous cement ; the one is hard, co-
herent, and finely granular, of a yellowish grey tinge, with spangles
of bright mica abundantly disseminated ; the other is characterised
by a looser and coarser texture, an inferior specific gravity, and
fewer spangles of mica.

DD. tulisas

[This article is applied by the Editor from the joint observations
of Mr. Buckland and himself, the route pursued by Dr. Berger,
not having allowed him to examine this formation in the points
which exhibit it to the greatest advantage. ]

This formation consists of beds of slate clay alternating with thin
‘seams of argillaceous limestone; the limestone is compact but not
crystalline, of a bluish colour passing into smoke grey; the fossils
which characterise it are cornua ammonis, gryphites, and the colum-

of the North of Ireland, 165

nar joints of the pentacrinus; this formation may be studied most
advantageously along the line of coast between Gerron point and
Lough Larne, on the east side of Antrim, where several sections of
it are exhibited. On the south of Gerron point the extensive bay of
Glenarm opens; the village of Glenarm itself is situated near the
south cape of the bay, between two lofty hills of chalk covered with
basalt ; the range with which these are connected sweeps in a bold
semicircle round the bay, receding considerably from the line of coast
which generally presents only a flat beach; towards the centre of
the bay, however, a low crag of red sandstone occurs, distin-
guished by the name of the red braes of Carnallock ; half way
between these and Glenarm, the clay of the lias formation may be
traced, interposed between the red sand and the green sand
which underlies the chalk. .

But this formation is far better displayed after doubling the Cape
of Glenarm in the cliffs beneath the deer park, about two miles south-
east from that village; here it emerges from under the chalk and
green sand, and exhibits a thickness exceeding 100 feet. Near the
outlet of Lough Larne lias has been traced in Port Muck, at the
north-east extremity of the island of Magee, and borings, engaged in
from the hopeless speculation of discovering coal, have proved its ex-
istence among the substrata in other parts of that island, where it rests
on red marle containing gypsum. On the western shore of Lough
Larne, lias occurs about one mile south from the town whence the
lough derives its name ; it skirts the margin of the lough for some
distance towards the south, but does not appear to rise many feet
above high water mark. Only one thin stratum of the limestone is
here visible ; this contains gryphites and pentacrinites,

We understood that lias had been traced in several places be-
tween Larne and Belfast. In Colin Glen, about four miles soutk-

166 Dr. BERGER on the Geological Features

south-west of that town, the mulattoe rests on a slate clay probably
of this formation. ,

The localities already cited range along the south eastern border
of the great basaltic and secondary area; the same formation ap-
pears also to exist towards the northern boundary. From speci-
mens which we examined in the collection of the Dublin Society,
we had reason to believe that this is the case in the neighbourhood
of Ballycastle, but we did not ourselves observe this formation in
situ in that point. About half way between Ballycastle and Bush-
mills near Ballintoy, the chalk formation rises sufficiently high to
disclose its substrata; a valley opening towards the sea, near
White Park, shews that they here consist of the slate clay of the lias
formation, with gryphites and ammonites. Farther east the chalk
cliffs again emerge from the level of the sea immediately beyond
Dunluce Castle, and continue to rise till they are broken off at the
commencement of Portrush Strand. As they here exhibit nearly
the same thickness which they possess near White Park, we are
naturally led to expect the recurrence of similar substrata near this
point ; and accordingly, in the peninsula of Portrush, a singular
rock is seen, divided by interposed masses of greenstone, but con-
taining ammonites and gryphites, and possessing exactly that cha-
racter which would be assumed by the slate clay before described,
if indurated by the action of heat. In the explanatory notes
accompanying the sections of the coast a more detailed account of
this peninsula will be found.

The cabinet of the Dublin Society contains specimens of lias
from the neighbourhood of Magilligan, about eight miles westward
from Portrush, and close to the north-west angle of the basaltic area.

of the North of Iréland. 167

E. Mulattoe or Green Sandstone.

To the general account of this rock given in the Introduction,
it may be added, that on treating different specimens with acids
they were found to contain about nine-tenths of calcareous matter,
the residuum consisting of green chloritic grains, mixed with quart-
zose sand or gravel.

The mulattoe is seen in Colin glen, a valley on the south-west
of Divis hill near Belfast, and in several other places on the slope
of that mountain ; it is evidently interposed between the slate clay
of the lias formation and the chalk. It occurs also at Cermoney,
about five miles north-east from Divis. The chloritic grains in
the mulattoe of Divis are small and very numerous, the calcareous
base greyish and compact; it is traversed by slender veins of
calcareous spar: besides the smaller grains of quartz, it contains a
few larger pebbles with a reddish tinge.

Since it is not quarried for any economical purpose, we have no
opportunity of ascertaining accurately the thickness or extent of
the bed.

It is seen however near Larne, and considerably further north
near Gerron point, occupying a position corresponding to that in
which it occurs near Belfast, and it seems highly probable that it
extends beneath the chalk throughout the intervals separating these
points ; indeed I am inclined to believe that where the series ap-
proaches to completeness, this member will seldom be found want-
ing.

In Murloch bay, where the line of chalk commences on the
east of the greenstone mass of Fairhead, a thin seam of quartzose
pebbles cemented by green sand, affords traces of this formation ;
it separates the chalk from a thick bed of red sand.

168 Dr. BerGeER on the Geological Features

Along the western escarpment of the basaltic mountains in Lon-
donderry, the mulattoe is seen underlying the chalk in Kedy
Donald and Ballyness hills. Between Ballyness and Benbradagh, at
the head of the vale of the Kelvin river, a wild circus opens, barred
on the north by basaltic ridges, and having the insulated primitive
district of Coolcroscrahan on the south: the Glen Ullin water and
Donavenny brook rise also within the area, and,flowing in a direc-
tion contrary to that of the Kelvin, join the Aghivey river itself,
tributary to the Bann. Within this area a remarkable bed of marle
occurs, which is mentioned here, on account of its containing nu-
merous green particles ; but it differs so essentially from the Mu-
lattoe in its chemical composition, containing only one-fiftieth of
calcareous matter, that it cannot with propriety, though resembling
it in external appearance, be considered as the same rock: the base
is a soft clay, greyish, with a slight red tinge; the structure
is thin slaty ; it contains some small worn quartz pebbles : the chalk
has not yet been traced in this district, but along the banks of
Donavenny brook, a breccia formed of chalk flints, imbedded in a
calcareous cement, and underlying the basalt, seems to indicate
its proximity. This brecciais probably connected with the aggre-
gation of flints, usually interposed between the basalt and chalk,
as described in the next article.

The subjoined list of the organic remains occurring in the Mu-
lattoe of Ireland, will be found to agree closely with those pre-
sented by the green sand in England.

of the North of Ireland. 169

GENERA. SPECIES.
SGlEMMITEN Eis. clea} steeds. Gils ein BALE Colin Glen and
Donald Hill
Venus? Lin. ....'fragment of ........ Colin glen
MOGITOS har sisi ta 0, Crista Galli sien « 5 hic Ibid. *
Z strea. 6 ks ase I EE 1 Oe ee Ree [bid.
wk eae tetera CrEyOHMelIS) 2 5.0 sjoe't = Ibid.
Peeten 22/3!).6 663! Mabiats Neo aes. Ibid
ANGINA tapas se - henson, dayne. ath Ibid
LR aR RRR, Gryphus, two varieties|Belfast Mountains
Miytilus « 2). Scsefinys Crista Galle 8.9. 2). Colin glen
DIG ssatieecere ss lithophagus ........
Lin. Tr. v. 8. p. 6.f. 1|[bid.
Cardium?......... RY, EDU elon Ibid
Betpulan cin. cpseslayee » t wditrpenasta. dtjs2 Ibid.
Dentalium .......{/hexangulum........ Ibid.
LAD Ree eR eee 2 nae = eee Carrickfergus
POON 5.2 acim clehvaicleladans”s ars wing's ‘a isyare Belfast Mountains
F. Chalk.

The chalk formation in Ireland has hitherto been frequently
distinguished by the name of white limestone, its compact texture
having caused those who were acquainted only with the superior
beds of the English chalk formation to hesitate in admitting their
identity : the occurrence of the cornu ammonis among the fossils
of the Irish chalk was also supposed to furnish another distinctive
character; in both these circumstances, however, it agrees with
the lower beds of the English chalk ; further, its geological position,
(reposing as it does on the same bed of calcareous sandstone, with
chloritic grains, which supports the English chalk) the analogy

Wiens rit. Y

170 Dr. BERGER on the Geological Features

of its fossils, and the absolute sameness of its general features,
will no longer permit us to describe by a distinct name, this im-
portant formation.

It need not excite any surprize to find the floetz trap incumbent
on a bed of such recent formation, since in the north of Italy it
may be seen to rest upon strata still less ancient, and analogous
to those which occur in the basins of London and of Paris.

The Irish chalk is seldom of a texture sufficiently loose to soil
the hand, and in the few instances where this does take place, it is
in a very slight degree: its general colour is either perfect white,
or white with a very slight tinge of yellow; towards the lower
beds it passes into an uniform ash colour, the texture then becomes
still more compact. It is sometimes traversed by slender veins of
calcareous spar, these are more frequent in the lower beds: it con-
tains (though in very small quantity) kidney shaped nodules of
iron pyrites; but the most striking of its imbedded contents are
the flinty nodules which traverse the mass in regular horizontal
strata, distant from each other, by an average interval, about two
feet and a half; the flints cease in the lowest beds. Among the
flints some of remarkable size, and of a regular and apparently
organic figure cccur ; these are known by the name of Paramou-
dra, and are also found in the chalk of Norfolk. It is superfluous
to describe farther the characters of these beds of flinty nodules
than by saying, that they are precisely the same with those pre-
sented in every English chalk pit.

The average thickness of the chalk formation in Ireland may
be estimated at between two and three hundred feet; the upper
beds seem to have been partially redissolved before the basaltic
mass was deposited upon them, since along the line of junc-
tion a confused aggregation of chalk flints exists, imbedded in the

of the North of Ireland. 171

lowest member of the trap deposit, which is usually a bed of
ochreous bole: the flints so imbedded have usually themselves ac-
quired a red tinge, apparently by percolation, from the oxidated
iron of the stratum in which they lie.

This aggregation of flints, bedded in red ochreous bole, forms at
Macgilligan, a stratum thirteen feet thick. It may be observed,
also, near Larne and near Belfast, and seems indeed of almost

universal occurrence.

List of organic remains found in the chalk of Ireland.

GENERA. SPECIES. PLACES.
Echinus ....cidaris mamillata.... Kenbaan Antrim; Slievegallion Derry.
Boutatuy #5 pigs bo 43 Pollen quarry near Agenloo Derry.
Terebratula.. vulgaris........... Ballyness Derry.
sulcata oc 0 0A es Ibid.
Pecten :..c1. . CARESS Rh 50? erarare aye 2, Ballycreem Derry.

The foregoing specimens closely agree with the fossils of the
English chalk.

Belemnites are common in most of the quarries opened on this
bed in Ireland: many of the bodies in the English chalk, once
supposed to be helemnites, are now regarded as the pallisadoe
spines of the echinus. Some few, however, are undoubted be-
lemnites ; the Irish specimens appear to be generally true belem-
nites.

Specimens of cornua ammonis, from five inches to one in
diameter, occur in the Pollen quarry ; but not having myself ex-
amined these, I cannot say how far they agree with some of the
very few varieties which are found in the lower strata of chalk in
England. The flinty nodules often contain fossils similar to those
of the surrounding chalk, and present, in addition to these, traces

of alcyonia.
y 2

172 Dr. BERGER on the Geological Features

The chalk is frequently traversed by basaltic dykes, and often
undergoes a remarkable alteration near the point of contact; where
this is the case the change sometimes extends eight or ten feet. from
the wall of the dyke, being at that point greatest, and thence gra-
dually decreasing till it becomes evanescent. The extreme effect
presents a dark-brown crystalline limestone, the crystals running in
flakes as large as those of coarse primitive limestone ; the next state
is saccharine, then fine grained and arenaceous ; a compact variety
having a porcellaneous aspect and a bluish-grey colour succeeds :
this towards the outer edge becomes yellowish white, and insen-
sibly graduates into the unaltered chalk. ‘The flints in the altered
chalk usually assume a grey yellowish colour; the altered chalk
is highly phosphorescent when subjected to heat.

Examples of this conversion of the chalk into granular marble
may be seen on the east slope of Divis mountain, near Belfast, in a
ravine to which Dr. Macdonald has given the name of Allan’s
Ravine, in honour of a mineralogical friend.

They are agatn exhibited in the neighbourhood of Glenarm,
where a singular compound dyke, consisting of three branches, tra-
verses the chalk: the included masses of which are altered in the
manner above described.

A dyke, very similar to the preceding, occurs in the isle of
Rathlin, near Church bay, and produces the same effect on the
chalk. ‘This dyke appears to be resumed on the opposite point of
the Antrim coast at Kenbaan head, where the granular marble is
likewise found. (See section, plate 10, and the explanatory notes.)
A dyke near Ballintoy affects the chalk in the same manner.

In the south-west extremity of Antrim the same marble is said to
occur near a whin dyke; the spot assigned is Bamersglen, near
Trummery, about one mile north-east from Moira.

of the North of Ireland. 173

Many more examples of this very interesting fact would, there is
little doubt, be found on further examination ; but those cited are
sufficient to prove that it is not unfrequent.

On the shore, a little to the west of the pier of Ballycastle, a
singular vein occurs in the chalk, which there forms the inferior
portion of a cliff capped with basalt; the basalt immediately in-
cumbent on the chalk approaches to the character of wacke. The
vein in question is calcareous, but contains imbedded balls of wacke ;
to the presence of which the difference of its characters from those
of the chalk that it traverses, may perhaps be attributed. The
limestone forming the vein is compact, breaking spontaneously
into parallelopipeds, the greater side of which is perpendicular
to the direction of the vein ; it contains about nine-tenths of cal-
careous matter, the residuum appearing to be clay, with some specks
of bright mica. The width of the vein is 17 feet; its direction
N.E. S.W. 83°.

_ Near the top of the stratum of chalk which crowns the cliffs of
Murloch bay, a bed five or six feet thick, of wacke approaching to
basalt, occurs interstratified with the chalk in a conformable position.

I shall now proceed to trace the outgoing of the chalk round the
basaltic area, beginning in the south-eastern quarter, and pursuing
it to the south-western, inserting in parallel columns the names of
places observed in the order of their succession along this route, and
the observations I had an opportunity of making concerning the
dip of the strata, the elevation of the formation, &c.

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176 Dr. BerGer on the Geological Features

In Carintogher and Cragnashoack the chalk appears to be want-
ing, and the basalt to repose immediately on the sandstone; but in
the insulated mass of secondary strata which cap the primitive mass
of Slieve Gallion (on the south of the great valley of denudation,
through which the Mayola flows) the chalk.again appears under-
neath the basalt, and there attains its greatest elevation, being
quarried at the considerable height of 1460 feet above the level of
the sea, the deposit is however thin and the strata much split.

On the east of Slieve Gallion is a valley about three miles in
breadth, occupied chiefly by red sand and marle, and succeeded
near Moneymore by a ridge of elevated ground, exhibiting chalk,
rising over the sandstone and surmounted by basalt ; this ridge
rises from Lough Neagh. At Ruskey it is but little raised above
the level of that lake; it ranges in a direction towards the north,
passing a little to the west of Magherafelt, a continuation of it
may be traced to the east of the insulated primitive district of
Coolcoscrahan, thence bending round the source of the Kelvin, and
joining the lofty chain before described near Ballyness. ‘The west-
ern escarpment of this ridge may be considered as limiting in that
direction the great basaltic area. Benbradagh, Cragnashoack and
Slieve Gallion, which lie without the boundary so assumed, form-, |
ing insulated and outlying masses, separated from the principal and
continuous basaltic region by vallies of denudation.

The elevation of this ridge does not appear to be very consider-
able ; it seems probable that the mulattoe will be found underlying
the chalk in this ridge as it does in the hilis with which it is
connected from Ballyness to Benyavenagh.

The south western limit of the area of chalk would be determined
by aline from Moneymore to Magheralin, this passes diagonally across
‘Lough Neagh, the strata which occur along it are of course concealed

of the North of Ireland. 177

but it is said that chalk makes its appearance at Temple Patrick,
near the north-east angle of the lake, being there exposed by the
excavation of the deep valley through which the Six mile water
flows.

Fro@rz TRAP.

This formation in Ulster comprises the following members.*
Tabular basalt,
Columnar basalt,

to

Greenstone,

ie go

Greystone,
Clinkstone porphyry,
Bole or red ochre,
Wacke,
Amygdaloidal wacke,
9. Wood coal.

ean

x

* The section given by Dr. Richardson of the cliffs near the Causeway well illustrates
the arrangement of these substances in constituting the aggregate mass of fleetz trap.

Feet
f. Esdsalt WUGely COIUMINAT (A... 3.2 occ cs Rocce wes eb eee esc: 60
2. Red ochre or bole ..........4. Y ROMERO ass - See iC 9
ae. Dasaltimreaplarly prismatic’ 5... 5.0.5. sna ctnceeesecedosee 60
Ase Colonna Dasalt; ask oh 0 otek eee wes ea Ste eter ae 7
5. Intermediate between bole and basalt.................. 8
6. Coarsely columnar basalt ......... korea t sprees odors ed . 10

7. Columnar basalt, the upper range of pillars at Bengore head 54
8. Irregularly prismatic basalt. In this bed the wacke and wood

coal of Port Noffer are situated.................20- 54
9. Columnar basalt, the stratum which forms the Causeway by

its intersection with the plane of the sea,............ 44
POs Ale GMTEMTOCHEC Cle erate ois circ te wei atee nee eek ts 22
ll.
ot Tabular basalt divided by thin seams of bole ............ 80
13.
14.
isd Tabular basalt occasionally containing zeolite............ 80
16.

Vou. 111, : z,

178 Dr. BERGER on the Geological Features

The following simple minerals occur imbedded in the rocks of
this series ; they are enumerated in the order of their more frequent

occurrence.
1. Granular olivine. 5. Zeolite, comprizing analcime,
mesotype, stilbite & chabasite.
2. Augite. 6. Iron pyrites.
3. Calcareous spar. 7. Glassy felspar.
4. Steatite. 8. Chalcedony; passing sometimes

into semi-opal. ,

Granular olivine in disseminated grains seldom fails in the tabular
basalt ; and sometimes occurs also in greystone. It has a remarkable
mode of decay, becoming tender, and iridescent.

Augite usually accompanies greenstone and sometimes greystone.
Steatite is almost exclusively limited to the prismatic basalt; and it
is likewise the only heterogeneous ingredient I have observed in it.
It exists in small round specks, of a bottle-green colour so dark, that
it is not easily discernible from the mass itself: it has a dull and
waxy appearance ; is soft, the streak greyish.

Glassy felspar characterizes the clinkstone porphyry. Calcareous
spar, zeolite, iron pyrites, and chalcedony usually occur in asso--
ciation with the preceding substances.

Since the floetz trap forms the superficial rock of the area we are
now to describe, it may be proper ,to insert in this place a list of the
most remarkable hills by which that surface is diversified, and some
other remarks on its general forms. In the list of hills, the same
order will be followed as before in tracing the chalk, beginning with
the south-east angle and ending with the south-west. The thickness
of the trap formation where it has been observed will be added.

of the North of Ireland.

Eastern chain from South to North.

Height of the hill
above the level of

the sea.
Dingsy. vis k oe Died eit 1475
CiRCA SR etegpe ae 1064
FRZHEWS=MMLE Sores. Sie cne eaN 1450
Slievemish ....,....... 2s acijeyh SOS
Deabaliagh » voi iawars «ode isa 1235
CCOWAP ANSE cies sicics.ss oes 1130
Ballypatrick .....2......004 955
Mnockileadt...r a ats: sejele 1820
Watnea dy pra tekiive vane) cicfsiess wie 535
CrOssoRireecisc ects sc crete ts 508

COS OROTS ei seks cael dine’
PS OMWTOTE cru ctsre ph acunagenere sit [5 (67s 328
Pleskinet year . EIS. SOL EE 354
Cliffs above Dunluce;.......: 157
Slieve Ard, the highest point of

the Island of Rathlin... . 372

PCN YaVENdeN, oy. a ws eels 1145
Le Pal et 1030
Domaldes-We a sce tae 1399
Benbradagh SPIRO), ORY 1569
Cairntogher fis 0/5 crackles «<5 1600
Cragnashoack........ seyeieie ee 1864
Sltevegallon Swiiseccs sews x0 a 1624

fia 5

eect ees e see eee ee

ere esse c eee eese

eeeecerereser es eeee

eee eo eree ee eer eser

eee rere er tore enese

ee

ere e reese ee an esee

eee e ees e sees eeee

@ree sees rere aesas

oreo eters eee eo seee

cee eee ree eee oeee

Ce ee

Ce |

Cr ey

Thickness of the
cap of trap.

The ridge above Moneymore has not been determined.

179

180 Dr. BERGER on the Geological Features

The above table will convey an accurate idea of the general
configuration of the circumference of the basaltic area.

The aggregate mass of all the formations constituting the third
system of mountains, appears to form a species of basin of which the
lowest point is situated near the center of the valley of the Ban ; hence
they rise, towards the south-east, where they lean against the exterior
chains of the Down mountains; towards the north-east, where the
primitive rocks of Cushleak emerge; and towards the south-west:
where they abut on the great central chain of Londonderry. In this
last direction, all the strata attain their greatest height, the chalk
standing in Slieve Gallion at 1460 feet and upwards, and the basalt
in Cragnashvack at 1864 feet. It is rather remarkable that the cap
of basalt grows gradually thinner in proceeding towards the same
point. On the north-east edge of this basin, the inferior limit of
the basalt, or its junction with the chalk, is 500 feet lower, but the
thickness of the cap of trap, increasing in the inverse ratio of this
diminution of level, raises the summit of Knocklead till it nearly
rivals Cragnashoack. In the south-east border, at Cave hill, the line
of junction is about 200 feet lower than in Knocklead; the cap of
trap is there very thin, but in the adjacent summit of Divis nearly
equals in thickness that which covers Knocklead. At Divis the line
of junction is depressed 200 feet below the level which it occupies
at Cave hill.

The high chains which form the borders of this basin on the east
and west, present a far less rapid slope towards its interior than
towards its circumference.

Thus between the towns of Belfast and-Antrim, the watershed or
highest point of the road which there crosses the eastern chain, is
situated three miles and a half from Belfast, and eight miles and a
half from Antrim, at the elevation of 9974 feet above the level of

of the North of Ireland. 181

the sea; the ascent therefore on the side of Belfast, which is that of
the outgoings of the strata, is 285 feet per mile, and 1174 only
on the Antrim side, which is that of the dip of the strata collectively
taken.

The Western chain, between Newton Limavaddy and Colerain,
was found by the same method to have a fall of 177 feet-per mile
on the side of its outgoing, and of 110 feet in that of its dip.

The detached summits of the principal basaltic mountains form
ridges which exhibit a.general tendency to arrange themselves in a.

direction pointing north and south. ~

1. Zabular Basalt.

This is the prevailing rock of the trap district under consideration,
occupying at least nine-tenths of its whole area.

It is disposed in strata, or rather beds, of considerable thickness.

The characters of this rock are too well known to need description.

Some of the strata contain imbedded specimens of most of the
simple minerals already enumerated as subordinate to the flcetz
trap formation; others are vesicular; others of an homogeneous
texture. The strata also vary materially in their degree of indu-
ration, and they are occasionally separated by beds of bole, amyg-
daloidal wacke, &c.

2, Columnar Basalt.

The strata of columnar basalt seem to occur almost exclusively
towards the northern boundary of the basaltic area.

182 Dr. BERGER on the Geological Features

The pillars are composed of the most compact and homogeneous
variety of basalt, containing a small quantity of steatite occasionally
imbedded in its mass, and possessing the property of being more or
less sonorous when struck by the hammer.

Besides the well known columnar strata exhibited by the Giarit’s’
Causeway and adjoining cliffs, of which the principal is 54 feet in
thickness, and a second 44 feet, similar strata are exhibited in the
following places. |

In Glen Ravel, at the distance of about four miles from Cushen-
dall, I observed in the bed of a stream flowing from the mountain
of Slieveance, an abrupt facade of tabular basalt, approaching the
columnar form, fronting the north-east quarter.

In the isle of Rathlin, there are several systems of pillars along
the northern coast: at Kenrammer, “ the thick Head,’ I counted
no less than seven in succession all nearly vertical, but none very
recular ; some were matted amongst themselves.

At Thivigh, “ the side-point,” there is a sort of headland sloping
down into the sea; it is covered with grass, but the section side-
ways exhibits two assemblages of square pillars, not unlike those
of Fair-head; the lower system comprehends those of the greatest
dimensions; the upper one, those that are the best defined.

Rhue-na-Scarse or Roanscarave, in the town-land of Craigmacagan,
presents another projecting point of land, with a real causeway, in
neatness hardly inferior to the Giant’s causeway itself, the pillars
being almost vertical; the pavement is nearly flat or horizontal.

At Doon-point, tabular basalt alone occurs; whence it appears
that the late Dr. Hamilton has mistaken it either for Thivigh or
Rhua-na-Scarse.

Near Ushet-haven, on the south-east side of a hill, named in
Irish Broagh-mor-na-Hoosid, there is another very elegant causeway:

of the North of Ireland. 183

it runs to the extent of four hundred and sixty yards in a direction
from north-east to south-west, coming up to the top of the hill
towards the latter point, and falling down the opposite way. The
pillars are five and six sided; a few have seven sides. I measured
two of the largest size; one of them was three feet, the other two -.
feet eight inches in diameter.

- Along the slope of the hill, the pillars are so completely dis-
engaged from the soil, that I could easily determine their PBs with
the horizon ;, I found it 22°.

On the main at Knocksoghey, the highest ridge of land between
Ballycastle-bay and. White-Park-bay, some floetz-trap pillars, most
of which are neatly defined, are quarried for building. Another
quarry of the same rock has been opened at Ballynastrade near
Ballintoy.

‘ Croaghmore, one of the hummocks that lies at the greatest distance
from the coast, is completely formed of an assemblage of pillars
almost vertical, and jointed as is usually the case.

In the town-land of Craigahulliar, one of the most beautiful
colonnades that can be seen lies under a mass of tabular basalt. Its _
extent is only one hundred and ninety feet, in a direction from
east-north-east to west-south-west, presenting its facade towards the
north-north-west: the pillars are from eighteen to fifteen feet in
height, and the individual joints of which they are composed, one
foot and a half ; most of them are five-sided, others have four and
six sides; they are remarkably sonorous.

I have remarked some rude attempts of the floetz trap to assume a
prismatic configuration at the bridge of Bushmills, at Magilligan,
and on the north-west side of Donald-hill, but not distinct enough
to be more particularly noticed.

It was natural to suppose that basaltic pillars, containing so

184 Dr. BERGER on the Geological Features

much iron and standing in a situation approaching to perpendicular
in many instances, might in time become natural magnets, with
the south pole uppermost and the north pole lowermost.

This however, I have never found to be the case; but I re-
marked a complete polarity in a rounded block of greenstone that
was lying rather deep in the ground on the top of Donald-hill in
the county of Londonderry: the needle of a pocket compass that
had been laid upon it went half way round and stood there per-
manently, the north pole of the needle pointing to the south and
the south pole to the north.

The pillars of Fairhead, and the adjacent summit of Fairhead,
are composed of greenstone containing augite.

Basalt passes into greenstone in the most imperceptible manner :
in the first stage, the felspar exists under the form of short, scaly
parts either white or greenish; the texture becomes more finely
granular and crystalline; the fracture in the great is not into flat
conchoidal pieces, but more usually into irregular and blunted
fragments. This finely granular and almost compact greenstone is
also more tough than common floetz-trap.

3. Greenstone.

It is dificult to determine the precise geognostic relations of the
basalt and greenstone in this district; but since the latter here
occupies an extent comparatively small, it must be considered as a
formation subordinate to the former ; whether however they form
distinct beds, or pass insensibly into each other by a gradual tran-
sition, is as yet undecided.

The greenstone columns of Fairhead and Cross hill are destitute

of the North East of Ireland. 185

of the regular articulations and neatness of form which distinguish
the basaltic pillars of the Causeway ; they form enormous prismatic
masses, often quadrilateral, and these latter appear to be formed of a
congeries of smaller prisms, aggregated in a manner which brings to
the mind the clustered assemblage of shafts forming a Gothic
column; the greatest length of these columns is not less than 250
feet ; the greenstone is highly crystallized, the concretions being dis-
tinct and large, and contains augite.

Slievemish, a remarkable mountain, which lies like a colassal land-
mark in the middle of the county, is from its basis to its summit
composed entirely of greenstone, thus forming a mass of nine
hundred feet in thickness.

Notwithstanding Slievemish has at a distance the appearance of a
cone, yet it is, like all the other mountains in Antrim, much more
extended in the direction from north to south than in a transverse
section: the ascent is steep and almost impracticable on the west
side, where we rise to the top by a succession of short terraces similar
to a flight of stairs.

The greenstone is here remarkably beautiful, being of a tender
mountain green, interspersed with crystals of augite and granular
olivine ; the fracture is in flat or scaly concretions: it lies in distinct
tabular masses two or three inches thick, perpendicular to the
horizon, or sometimes with a slight dip to the westward.

The mountain of Teabuliagh near Newton Glens, has a cap of
finely granular greenstone five hundred feet in thickness,

The rock which overlies the chalk at Magheralin, may perhaps
with greater propriety be arranged as greenstone than basalt.

VOL. III. Qa

186 Dr. BERGER on the Geological Features

4. Greystone.

The top of Squires hill and of Cave hill, near Belfast, are both
composed of this rock. |

5. Clinkstone Porphyry.

The little table-land forming the summit of Divis mountain con-
sists of a beautiful clinkstone porphyry of a reddish brown colour,
containing elongated lamellar crystals of glassy felspar, and concre-
tions of bluish white chalcedony: the rock is very sonorous. A
variety of clinkstone porphyry also occurs in the neighbourhood of
the old red sandstone, near Newton Glens, so situated that it is
difficult to pronounce what is its position or geognostic relations
with regard to that rock: it will be more particularly described in
the explanatory notes on the section.

The porphyries of Sandy-brae, &c. in the interior of the basaltic
are, of which the geognostic situation is likewise uncertain, are
referred to a separate article at the end of these extracts.

”*

G6. Bole or Ochre

, Occurs in beds. of various thickness, alternating with and under-
sane the basaltic strata in the cliffs near the Giant’s Causeway ;
in Cave hill, on Macgillizan, along the east side of Ushet lough
in the isle of Rathlin, and in several other places. Although the
specific gravity of the bole is low it contains a great proportion of
iron, (acting powerfully on the magnet) and might with propriety
be classed among the earthy and ochrey ironstones.

of the North East of Ireland. 187

Near the Giant’s Causeway it is confined to the lower portion of
the cliffs, where beds of it in various states are seen, sometimes’
assuming the character of a decided red ochre, sometimes variegated.
red and cream yellow, containing imbedded heterogenous portions,
wearing at a small distance the external appearance of agates, but
when examined found to be as tender as the softest steatite. Specific .—
gravity 1,92. :

Similar characters apply to the bole in other places. The lowest
bed of the trap formation where it comes in contact with the upper
-surface of the chalk, and contains chalk flints imbedded in its mass,
is most generally a red ochrey bole. |

7. Wacke.

This rock appears to be of extremely rare occurrence in the Ulster
trap series; it is found however in Portnoffer near the Causeway,
underlying the upper stratum of columnar basalt, and alternating
with the wood coal described in article 9; the thickness of the
whole amounting to eight feet: it forms vesicular concretions of a
trapezoidal or rounded figure; without coherence ; texture dull and
earthy, with a few specks of mica; the colour varies from yellowish
grey to brownish grey, apparently derived from iron ochre. The bed
or horizontal dyke of wacke traversing the chalk cliff at Murlough
bay has before been noticed. A seam of wacke, not more than
three or four inches thick, is interposed between the greenstone and
sandstone of Cross hill. .

2a2Z

188 Dr. BERGER on the Geological Features

8. Amygdaloidal Wacke.

Colour variegaced reddish or greyish brown; fracture dull and
scaly ; soft, owing to seatite which occurs both in grains and in
larger disseminated concretions.

It also contains radiated zeolite in considerable abundance, in
concretions of all sizes: and cubic zeolite has been found at
Benyavenagh, but is very rare.

Chalcedony is likewise found imbedded in this rock, but is not
very common.

9. Wood Coal

Has been found in seams varying from two inches to four or five
feet in thickness, alternating with trap rocks near Ballintoy; associated
with the bed of wacke, underlying the upper columnar stratum in the
cliffs of Portnoffer on the east of the Giant’s Causeway, at Killymorris
near the center of the basaltic area, and at Portmore and other places
along the eastern shore of Lough Neagh. At Portmore the beds
are said to exceed considerably in thickness the dimensions above
given. The texture of the wood is often remarkably distinct, and
indicates that it is a species of fir. It has even been asserted that
the roots and branches of the trees could be traced.

The wood coal at Portnoffer has the exterior surface of some of
its fragments penetrated to a certain depth by small nests of augite
imperfectly crystallized.

of the North East of Ireland. 189

ADDENDA.

1. Account of certain porphyritic rocks of doubtful formation.
2. Alluvial formations.

, ; Porphyry of Sandy-brae.

Near the centre of the basaltic area, and about seven miles north
north-east from Antrim, a very remarkable district occurs, in which
a reddish variety of clay porphyry prevails.

This district is situated between Templepatrick on the south and

Kells and Connor on the north, including an area of about four
English miles ; proceeding from Connor in a westerly direction, you
first meet the porphyry formation at Carnecome, scarcely a mile
distant from that village, and continue upon it for about three miles,
as far as the source of a small brook caJ!ed Loonburn, which empties
itself into the Six mile water above Templepatrick. :
- Numerous small hills are scattered over this tract; Sandy-brae,
Brown Dodd, Tardree, Forthill, and Carnearny, are the names of
the most considerable. These are all low hummocks, exhibiting in
their outline a striking approach to regular segments of circles, and,
as Dr..Richardson has well remarked, strongly contrasted with the
basaltic ridges which every where surround the porphyritic area, and.
uniformly present an abrupt escarpment on the one side, and a gentle
slope on the other. The hill of Sandy-brae rises 537 feet above
Doagh, which, from its situation relatively to Lough Neagh, cannot
be estimated at less than 200 feet above the level of the sea.

The clay porphyry of this district has a reddish brown basis, con-
taining imbedded in it concretions of smoky quartz, earthy and
glassy crystals of felspar, and olivine. Specific gravity 2,43.

190 Dr. BERGER on the Geological Features

It is usually much weathered, its decomposition giving rise to a
red sandy soil, whence the district derives its name.

At Carnecome is a large standing block of clay porphyry, ‘of an
ash-grey colour, containing the same ingredients as that above
described.

Pitchstone porphyry and pearlstone porphyry occur apparently as
subordinate members in this formation.

Two large masses of each variety may be seen at the bridge across
the Loonburn, on the road from Connor to Doagh.

Pitchstone Porphyry of Sandy-brae.

The most sound and interior part is bluish black, possessing a
splendent and vitreous lustre: its specific gravity is 2,52; a little
nearer to the surface it passes to olive green, with a waxy texture,
and has a specific gravity of 2,50; at the surface it appears yellowish
green and rather earthy, with a specific gravity of 2,40; all these
different shades sometimes occur in the same specimen, and appear
evidently to result from decay.

Engaged in the basis round concretions of smoky and vitreous
quartz, with lamellar crystals of glassy felspar possessing a yellowish
tinge occur. Common opal, nearly approaching to precious opal,
accompanies this pitchstone porphyry; it is either disseminated in
plates or in small strings.

Pearlstone Porphyry of Sandy-brae.

The texture is formed of vesicular and distinct concretions loosely
coherent, of an elongated or irregular shape, the angles being smooth

of the North East of Ireland. 191

and rounded. Their colour is smoke-grey or bluish, with a pearly
lustre. ‘They seem formed of concentric and very thin coats. The
fracture of this mineral is imperfectly conchoidal ; it cuts glass but
faintly, and emits a faint argillaceous smell when breathed upon.
Fragments, exposed to the blowpipe, intumesce to four or five times
their first volume, fusing into a foamy and light glass, not unlike
pumhice stone. Radiated zeolite is the only fossil I am acquainted
with that resembles pearlstone in the characters of fusion. The
specific gravity of two different specimens, | found 2,38.

About 76 miles to the north of this district, at Ballycloghan, two
miles north-west from the village of Broughshane, there is a bed of
clay porphyry extending towards Slieve Mish on the south-east ; it
is quarried as a freestone, and when raised in thick slabs, is used for
window seats.

The basis is compact and sometimes earthy, of a greyish white
colour; it contains imbedded concretions of smoky quartz, lamellar
crystals of white felspar, and a few interspersed plates of brown
mica; it adheres to the tongue slightly, and fuses into a transparent
but frothy enamel; the specific gravity is 2,43.

The occurrence of a porphyritic district, surrounded on all sides
by a vast area of basalt, must be considered as one of the most
singular facts which the country we have examined presents. The
question to what formation do these porphyritic rocks belong, im-
mediately suggests itself, but the materials which observation has
hithereo afforded cannot be considered as authorizing any decided
answer. Many geologists, among whom it will be sufficient to
mention Dr. Macdonnel and Dr. Richardson, consider them as re-
ferable to the class of transition or primitive rocks, and regard their
appearance in this situation as the result of a vast denudation which

192 Dr. BERGER on the Geological Features

has stripped away the basaltic masses which once covered them.
This opinion seems principally grounded on the resemblance between
these porphyries and those occurring in more ancient countries.

‘Another opinion represents these rocks as subordinate members in
the floetz trap formation. In favor of this it is urged that the general
dip of the strata constituting the great basin of the basaltic area must
(unless we suppose them to have been affected by a great dislocation
and elevation) have carried the substrata on which the trap reposes
to a much lower level than that which is actually occupied by the
hillocks in question ; and it has been asserted as a corroborating fact
that the porphyry is actually seen to rest upon the basalt in one of
the ravines which traverses the district, while still lower at Temple-
patrick, the stratum of chalk on which the basalt really reposes makes
its appearance.

The occurrence of similar rocks subordinate to fleetz trap is by
no means unexampled in other countries. Near Newry a narrow
dyke of pitchstone porphyry extends for half a mile to the west,
and in a continuation of the same line clay porphyry occurs. This
dyke traverses sienitic rocks: an account of it is given in Dr, Fitton’s
notes on the mineralogy of the vicinity of Dublin, p. 53.

A singular formation of clay porphyry approaching to clinkstone.
porphyry occurs near Newtonglens in Antrim, seemingly associated
with the old red sandstone; it is particularly described in the notes
on the sections of the coast, appended to the present paper.

of the North of Ivéland. 193

2. Alluvial Formations,*

At B. Macrevan, in the county of Antrim, half way between-
Glenevey and Lough Neagh, bituminous wood in disseminated pieces
loosely imbedded in a loamy soil has been found.

Two shafts, each sixty feet deep, were formerly sunk to obtain
_it, but are now abandoned, the stock being exhausted. I however

procured some specimens. The wood has €vidently retained its
fibrous texture, and burns with a vivid flame ; specific gravity 1,124.

Not far from B. Macrevan, at B. Vorally, in Sandy Bay, there
are still remaining on the shore, a few stumps of bituminized wood,
the fissures of which are penetrated by silex, and sometimes even
lined by quartz crystals. It does not flame, and its’specific gravity,
from the quartz it contains, amounts to 2,267.

It was once the general opinion that the waters of the lough had the
property of petrifying, and that the quartz contained in the bitumi-
nous wood of Sandy Bay had been deposited from them. The ex-

periments however, made by Mr. Tennant during his stay at Belfast,
appear to discountenance that belief, since he found no traces of
silica whatsoever in the water of the lough. +

* On the shore of Belfast Lough, traces of ati anciont forest have been discovered
beneath a peat bog. Here a singular phenomenon (first communicated to the Geological
Society by Dr. Mac Donnel) occurs, hazel nuts being found, the kernels of which are
often converted into calcareous spar, while the shells remain unaltered. I am not aware
that the remains of the elk, so common in the alluvial districts of other parts of Ireland,
have yet been found in this quarter.

+ As this is the only part of Dr. Berger’s notes, in which Lough Neagh is mentioned, I
have taken the opportunity of stating some facts concerning it.

Its height above the level of the sea is 132 fect.

Its greatest depth between Arboe and Gartrea points néarly in the centre, 45 feet

Its greatest length from north-west to south-cast, 19 miles 6 furlongs.

Its superficial contents 97,775 acres.

A constant tradition has prevailed in Ireland, at least sin¢e thé days of Giraldus Cam-
brensis, that it owes its origin to some violent convulsion.

The northern and eastern shores of the lough presents several sandy beaches, in which
fine chalcedonic pebbles are found.

VOL, III. 2B

194 Dr. BERGER on the Geological Features

The penetration of the wood by the siliceous matter is sometimes
compleat ; sometimes one extremity of the same fragment is thus
petrified while the other remains in a ligneous state. The oak, the
holly, and the hazel appear to have been the trees thus affected.

A phenomenon occurring in some caverns near the Black Rock,
on the south of Church Bay in the isle of Rathlin, may be properly
referred to this article, ;

These caverns (four in number) although excavated in the ba-
saltic rock and at a point remote from any calcareous formation, are
yet invested with calcareous stalactites, depending from their roofs,
and by their droppings: upon the floor depositing a crust of about an
inch in thickness.

This circumstance appears worthy of attention, since the calca-
reous matter seems evidently, from the situation of the caverns,
to have been derived from that which enters as a chemical ingre-
dient into the composition of the basaltic rock, separated from the
mass and deposited in its present situation by the percolation of
water which the rain or springs must have furnished.

It proves therefore the permeability of basalt which has sometimes
been denied, and gives countenance to the opinions of those who
consider the nodules of calcareous spar and zeolite, occurring in the
amygdaloidal varieties, as the results of an infiltration which has gra~
dually filled up what were once vesicular cavities ; it is remarkable
that the substances so occurring are such as the chemical constitution
of the matrix would qualify it to afford by a similar process ; and in
the instances above described, that very process may be detected
passing under our immediate observation.

A vesicular variety of basalt, of which the pores contain water,
occurs at Ballylaglan on the north of Coleraine. Dr. Richardson
has mentioned it as a proof of the aqueous origin of basalt, believing

of the North of Ireland. 195

it impossible for the water contained to have insinuated itself since
the original consolidation of the rock ; but it has been found that by ©
heating this basalt, the water may readily be driven off, and doubtless
the same pores which allow its escape would with equal facility
permit its entrance,

/

196 The Rev. W. CoNYBEARE ox

Descriptive Notes referring to the Outline of Sections
Presented by a part of the coasts of Antrim and Derry,
Collected by the Rev. W. Coxyzeare, M.G:S.

From the joint Observations of

The Rev. W. Bucktann, M.G.S. Reader in Mineralogy to the
University of Oxford,

And himself, during a Tour in the Summer of 1813.

The Section, Plates 10. 10*. accompanying these notes, exhibits
a line of coast extending rather more than fifty miles from the
promontory on the south of Glenarm* in Antrim, to the strand of
Macgilligan in Londonderry, where the basaltic mountains receding
to the south finally quit the vicinity of the sea.

* The first point in which the cliffs of the Antrim coast expose sections of the basaltic
rocks, is Blackhead, on the south-east of the peninsula of Magee ; this point is (following
the indented line of the coast) more than twenty miles to the south of that at which the
delineations accompanying this paper commence: our information concerning that interval
not being sufficiently precise to admit its being exhibited in such a form.

The following short notice will however contribute in some measure to supply the
deficiency, and being prefixed to the descriptions in the text will render them a continuous
survey of all that part of the basaltic area which presents a precipitous face towards
the sea.

From Blackhead the eastern coast of the peninsula of Magee exhibits a long and lofty
range of basaltic cliffs called the Gobbins, extending nearly eight miles towards Portmuck
at the north-east extremity of the peninsula; near this point the chalk emerges from
beneath the basalt, and the lias from beneath the chalk. Hence to the mouth of Larne
Jough the cliffs cease, the hills rising with a gradual acclivity from the beach; the same

the North East of Ireland. 197

Throughout this space the cliffs present a series of highly
interesting and instructive sections, which indeed leave us little to -
desire in elucidating the structure of this important district, since
they traverse and expose in succession all its constituent formations
from the mica slate to the floetz trap.

In endeavouring to lay before the Society a transcript from
these records of nature, the general principle adopted has been that
of a combined series of elevations, projected upon vertical planes
of which the direction is continually shifting so as to be always
parallel) to the greater flexures of the coast: but, since it appeared
in many instances that the introduction of perspective would
convey a clearer idea of the phenomena to be represented, the
principle above laid down has often been departed from; and the
delineations in their present state cannot be considered either as
elevations or perspective views, in any strict sense. Two principles
which cannot in truth be combined have certainly thus been forced
together, but it is hoped usefully so with reference to the infor-
mation to be conveyed.

To those who consider the varying aspects assumed by the
same points when viewed under different angles in sailing past
them, it must be obvious that much of incorrectness will of
necessity intrude into the attempt of persons not practically ex-

character is applicable to the opposite side of the lough near Larne: the chalk and lias
continue to occupy the level of the sea through this space, but about two miles to the
north of Larne the chalk again sinks beneath the low basaltic cliff of Black-cave-head ;
a ridge of the same rock extends from hence skirting the beach for three miles to
Ballygelly head, a promontory exhibiting rude and irregular columns ; near this point the
inferior strata emerge, but from the flatness of the coast heing flat do not render themselves
distinctly visible. About three miles beyond Ballygelly-head however the red marle (No. 4
of the Intreduction) may be traced, and about two miles further the lias begins te show
itself in the southern extremity of the Deer park hill of Glenarm: this is the point at

which the engraved section commences.

198 The Rev. W. CoNYBEARE on

perienced in surveying, to construct such projections as have been
described from their detached sketches; and to such objections it is
felt that the present example lies particularly open: it is indeed
offered merely as an approximation to a correct representation.
Such as it is, however, it is presented to the Society, in the belief
that the errors are not of a nature to interfere with fidelity
in laying down the great geological features which distinguish this
interesting coast, and that these features are in themselves $0
important as to render any delineation which might in this respect

(however imperfect in others) pretend to some degree of accuracy,
desirable,

y

In describing these sections the very ample information collected
by Dr. Berger concerning this district, will render it unnecessary to
exceed the limits of a rapid survey; this I shall commence at the
south-east extremity of the line represented, proceeding towards
the north-west.

In this direction the lias formation is seen at the extremity of
the section occupying the lower regions of the promontory over
which the Deer park of Glenarm extends, near its southern point ;
the ground here ascends with a rapid slope, above which cliffs of
chalk covered by basalt rise to a considerable height: advancing
towards the north the lias dips beneath the level of the sea, and
the beach is skirted by a chalk cliff.

On doubling the promontory, Glenarm presents itself situated
in a narrow valley bounded on the east. by the Deer park hill, and
on the west by Bellaire hill, both of which in their sections towards
the sea exhibit cliffs of chalk covered by basaltic platforms. The
distant hill seen rising above the opening of this valley, is Slieve
Mish, it consists entirely of greenstone. Near Glenarm is the
remarkable compound dyke mentioned in page 172.

the North East of Ireland. 199

The headlands of Glenarm on the south, and the bold promon-
tory of Gerron on the north, include a bay which extends for six.
miles between them. Towards the centre of this bay the coast is
generally flat, but a low bank of trifling extent called the braes of
Carnalloch, here displays the red marle and sandstone (No. 4. of
the Introduction); and the lias and green sand (No. 3 and 2.) may
be traced between the chalk of Bellaire hill and this point; these
formations occupy the base of the mountains which are seen
skirting this bay at a small distance inland, and of which the
superior regions are exclusively composed of rocks of the floetz
trap formation. ‘The summits of these mountains considerably
exceed 1000 feet in height. The cliffs of Gerron point are formed
by the abrupt termination against the coast of a ridge connected
with them.

These cliffs exhibit basalt towards the summit, and chalk in their
central regions; the beds on which the chalk reposes are concealed
along the base of the promontory by enormous masses of the
superior strata, which have subsided in this direction and form a
’ range of advanced terraces, causing the headland when viewed at a
small distance, to appear as if composed of four strata alternately
chalk and basalt. ‘Those who have visited the southern coast of the
Isle of Wight will on seeing Gerron point be strongly reminded of
the similar subsidence there distinguished by the name of the
under-cliff.

After doubling Gerron point a scene of the greatest magnificence
gradually discloses itself; the ridge running westward from Gerron
is seen extending far inland on the south of the valley of Glenarif
and crowned by the conical summit of Cruach-a-Crue; while on
the opposite side of that valley a similar but more lofty ridge

terminates in the singular mountain of Lurgethan, which appears as

200 The Rev. W. ConyBEARE on

the frtistim of an enormous cone of great height and comparatively
narrow base.

Both Cruach-a-Crue and Lurgethan present thick basaltic masses
cn their summits, resting at considerable elevations on strata of
chalk; in the former mountain the lower beds are concealed by
grassy slopes, in the latter red sandstone is exhibited in several points
towards its central region: here probably a more full examination
might detect and -ascertain the thickness of the green sand and lias,
which from the general structure of the district might be expected
to intervene between the chalk and red sand; the spot certainly
appears very favorable for such an enquiry.

At the foot of Lurgethan the coast presents two low cliffs divided
by a valley which affords a passage towards the sea to a small rivulet;
these cliffs are composed of red sandstone and a conglomerate con-
taining rounded fragments of quartz, the rock being altogether
similar to that which Dr. Berger has described as the old red sand~
stone in the neighbouring hill on which Cushendon church is built ;
since, between these cliffs and the sections visible in the precipices
which oceur near the summit of Lurgethan, a considerable space |
intervenes through which the substrata are concealed by grassy
or cultivated slopes, it is not easy to determine the geological
relations existing between the sandstone in the higher region and
that on the level of the sea.

On the most southern of these cliffs neat the strand at the mouth
of the Glenarif river stand the remains of an old fortification known
by the name of Red bay Castle; close to this spot several basaltic
dykes traverse the conglomerate, one of these, remarkable for its
great thickness, having resisted the action of the waves which have
encroached considerably on the adjacent cliffs, presents some bold
detached crags projecting from the beach. The conglomerate forms

the North East of Ireland. 201

ing the wall of the dyke has undergone a great degree of induration,
its cement assuming the appearance of a compact hornstone; thus it
has been enabled to oppose to the sea a resistance almost equal to
that of the basalt itself, and is still seen adhering on the sides of the
advanced crags above mentioned.

From the most northerly of the two cliffs a ridge extends
towards the ascent of Lurgethan on the south-west, running through
the townland of Killnadore; in several points along this ridge, and
particularly at Nockans and Tully, a very remarkable formation of
porphyry may be traced. Dr. Berger* considers it as clinkstone
porphyry and describes two varieties here noticed by him; one of
them distinguished by a reddish brown and the other by a bluish grey
colour, both containing concretions of glassy quartz and of calcareous
spar, the latter of which in the first variety occurs in the form
of detached crystals, but forms veins in the second. He adds that
it crops out in independent masses. He mentions also Court Mar-
tin, an old entrenchment near Cushendahl, on the road to
Cushendon, as another locality of the porphyry.

From the observations made by Mr. Buckland and myself on
these rocks we were induced to believe that they were associated
with and subordinate to the old red sandstone. ‘The position of the
ridge of Killnadore is distinctly indicated in the section.

On the north of this ridge is the mouth of the river Balyeemin
on which the little village known by the double name of Newton

* In an earlier part of the paper it was erroneously stated that this porphyry had
escaped Dr. Berger’s notice, and the editor did not discover his mistake till the state of
the press rendered it necessary to substitute acknowledgment for correction. His over-
sight arose from the circumstance of its being described among the floetz trap series,
though its connection with the old red sandstone and its position near the foot of Lur-
gethan, while the floetz trap is confined to the summit of that mountain, certainly
renders its introduction in such a place an act of very questionable propriety.

VW OE; ITI. Ze

202 The Rev. W. CoNYBEARE on

Glens or Cushendahl is situated ; the loftier ridge of Lurgethan also
runs to the west forming a bold amphitheatre of beds skirting the
southern bank of that river, and at length joining the still more
elevated mountain of Teabuliagh which extends between the con-
fluence of the Ballyeemin and the Glenaan a tributary streamlet.
The summit of Teabuliagh exhibits basalt, chalk, and red sandstone ;
and from hence these formations continue to crown the mountain
chain which runs at the distance of about six miles from the sea,
while the lower hills which occur nearer the coast are occupied by
rocks of much greater antiquity.

Returning to Cushendall and tracing these as exhibited in the
section of the cliffs, the old red sandstone and conglomerate (fully
described page 149) lines the coast as far as the bay of Cushendon ;
Near its termination at this point it is worn into many grotesque
forms, and presents considerable caverns: here Mr. Buckland ob-
served that the cement of the conglomerate often passed from a
mechanical to a chemical state, and assumed all the characters of
regular clay porphyry of a reddish colour, which appears to indicate
the true relations of the porphyry at Killnadore.

On the north of Cushendon point the valley of Glendun is seen
penetrating far into the country; through this valley the mica slate
makes its appearance underlying the old red sandstone. ‘The
mountains in the back ground are a continuation of the secondary
range from Teabuliagh and are of similar constitution.

The cliffs of. Cushleak ranging from the mouth of the Glendun
river to Murloch bay present mica slate, containing subordinate
beds of primitive limestone, syenite, and felspar porphyry.

The hills rising above these cliffs, as they approach Murloch
bay, become covered with beds of red sandstone and chalk towards

their summits, and some of the highest points exhibit caps of

the North East of Treland. 203

basalt. It is highly desirable that the slopes of these hills should
be carefully explored ; by examining the channels furrowed in their -
sides by the wintry torrents, we might hope to ascertain the whole
series of rocks here intervening between the primitive formations
and chalk.

Murloch bay is bounded on the south by a promontory, which
exhibits in the cliffs at its base beds of mica slate dipping towards
the north-west under an angle of 45°; but immense slopes of debris
(consisting mostly of primitive rocks) interfere to prevent the pos-
sibility of determining the structure of the lower regions of the
cliff as soon as the bay is entered. Above these slopes red sandstone
is seen supporting chalk ; the former rock attains the elevation of
560 feet above the beach, the latter extends to the summit of
the cliff about one hundred feet higher: between the red sand and
the chalk a thin bed of green sand, cementing quartzose pebbles,
may be traced. The bed of wacké here occurring in the chalk,
has been noticed, page173, and several whin dykes are observable tra-
versing the red sand. The most remarkable objects on the beach are
a large basaltic dyke, which rises in a projecting crag; and
still further to the north, near the centre of the bay, the detached
conical mount of Drimnakill, which is formed by a vast subsided
mass of columnar greenstone, the columns being thrown con-
fusedly together in every possible direction. Near the whin dykea
conglomerate, resembling that of Cushendon, may be’ seen; so
that this rock appears on either side to skirt the primitive forma-
tions of Cushleak.

Beyond the mount of Drimnakill, the lower parts of the cliffs
are still concealed by slopes of debris, among which subsided masses
of columnar greenstone form the prevailing feature ; and near this
2c2Z

204 The Rev. W. ConyBEARE on

point bold and lofty precipices of that rock take place of the chalk
anid red sandstone in the higher region, and, stretching to the north,
constitute the well-known promontory of Fairhead, which bounds
Murloch bay on that side.

It is greatly to be regretted, that the convulsions of which this
bay appears to have been the theatre, having covered the regular
strata with shattered fragments and piles of ruin, heaped together
in the wildest confusion, have thrown an impenetrable obscurity
over its structure, which, from the narrow space in which so many
formations are successively exhibited, must be regarded as more
important than that of any other point on this coast.

From this cause it is impossible to ascertain the exact relations
of the greenstone at this point with the chalk and red sand. The
general appearance is, that the mass of greenstone abuts abruptly
against that of the sandstone, both being placed at the same level.
It has been said that the greenstone and sandstone are here to be
observed, alternating with each other. (See notes to the poem of
the Giant’s Causeway, by Mr. Drummond.) But it may be
questioned whether this representation is not founded on a hasty
view of some of the subsided masses above mentioned. The
greenstone, where it first appears, exhibits two columnar strata,
separated by a bed of amorphous greenstone.

Near the point where the greenstone is lost, we observed the
traces of adits formerly driven into the sandstone in search of coal,
beds of which appear to occur among the lower members of the
sandstone formation. The position of one of these adits is such as
to afford some countenance to the supposition, that the greenstone
and sandstone here alternate; and, since a thin horizontal bed of
trap certainly does occur interstratified with the coal measures on
the other side of Fairhead, such an opinion cannot be rejected with-

out further examination.

the North East of Ireland. 205

It may be conjectured that the coal measures underlie the green-
stone through the entire range of Fairhead, since they again make .
their appearance beneath it on the east side of the promontory ; but
the whole of its base is too much encumbered with debris to allow
of our ascertaining this point. On the west side, at a lower
level than the’coal measures, we noticed a ledge of clay porphyry
running out to sea; this rock is probably analogous to the por-
phyries of Killnadore.

The columnar greenstone of Fairhead, and the coal measures
which underlie that rock in Gobb cliff, have been already de-
scribed*, and I have to mention but very few additional circumstances,
principally relating to the whin dykes which traverse that cliff;
of these dykes, the first in advancing from the east, is Carrick Mawr,
“ the great crag,” a name well deserved by its dimensions: it forms
a broad causeway, traversing the beach and terminating in a nearly
insulated mass of rocks rising about thirty feet ; of this mass only
the central line consists of the dyke itself, the sides being evidently
composed of portions of the strata traversed by it, but much altered
in their character and degree of induration by its contact. These
beds appear to have been chiefly derived from the slate clay of the
coal measures, which has become so compact as to assume the cha-
racter of flinty slate. In one point this rock may be seen on one
side of the dyke, and on the other the sandstone grit, which usually
accompanies the coal beds, also in a highly indurated state: its
colour changed from red to white, and its mass penetrated by

* It should be noticed, that in the section all the coal measures are coloured with a
dark tint, though this in fact belongs only to the coal itself and to the slate clay; the
thick beds of red sandstone which alternate with these strata form the predominating

features of the cliff.
This system of colouring has been adopted, becouse it seemed necessary to distinguish

the coal measures from the red sandstone not containing coal.

206 The Rev. W. CONYBEARE o”

minute grains of iron pyrites. At fifteen yards distance from the
dyke the alteration ceases, and the sandstone resumes its usual cha-
racter, becoming reddish and destitute of pyrites. Where the dyke
traverses the great insulated mass of slate, it is very irregular both
in thickness and direction. The works of Gob colliery have reached
this dyke 500 yards inland from the face of the cliff: the coal is
altered by it toa considerable distance from its point of contact, being
reduced to the state of a cinder, which can be employed only for burn-
ing lime. ‘This dyke throws out the measures of Gob colliery, which
are not recovered on its eastern side: its breadth is about 12 feet
where it comes to the surface of the cliff, but varies considerably in
different parts of its course. ;

Immediately behind Carrick Mawr, an opening may be seen in
the cliff which forms the channel of a torrent ; pursuing this inland
for the distance of about a mile it is found to issue from a small
lake surrounded with basaltic cliffs. We were ourselves prevented
from visiting this spot, but from the descriptions we received of it
were led to wonder, that none of those who consider this country
as volcanic had selected it as a crater.

At some distance east from Carrick Mawr dyke is the Saltpans
dyke, which also throws out the coal of Gob mine on the west ; its
breadth is eight yards. Still further is a thin dyke; both these
alter the coal. North Star dyke follows. This is often cut
through in the collieries, its breadth is eight yards: it does not
shift the coal, but reduces it to cinder for nine feet on each side of
its contact.

Where the cliff declines towards Ballycastle, the coal measures
terminate abruptly, and are succeeded by trap rocks. It seems that
this position must have been produced by a fault and subsidence.

Near Ballycastle a broad valley opens into the interior to-

the North East of Ireland, 207

wards the south and east. This valley is principally occupied
by the red sandstone, which, in those directions terminates against .
the mica slate, forming the base of Knocklead (the round-backed
mountain seen in the distance) and extending thus far in conti-
nuation of the primitive district already described in Cush-
leak. Between 4 and 500 feet on the ascent of this mountain, a
bed of primitive limestone may be traced. Above this, through an
interval of about 400 feet, the strata have not been ascertained ; but
probably the red sandstone, and perhaps also the lias and mulattoe,
may be found in this space, since the chalk appears at the elevation
of between 8 and 900 feet ; and the whole is crowned by a cap of
basalt, 980 feet in thickness.

On the eastern side of Ballycastle bay, the basalt rises into low
cliffs, and the substratum of chalk emerges from the level of the
sea, but soon sinks again.* In this interval the vein of wacke and
compact limestone, described by Dr. Berger, page 172, occurs ; from
_hence to Kenbaan there is nothing that requires particular at-
tention.

* I cannot more clearly describe the general arrangement of the chalk and basalt, as
displayed on the Antrim coast, than by transcribing the following paragraph from the late
Mr. Hamilton’s Letters, a work which may be classed with Mr. White’s well-known
letters on the Natural History of Selborne, as one of the most elegant models which our
language possesses of writing upon such subjects; and as affording one of the few ex-
amples which prove that they are capable of being treated in such a manner as shall
render them not only interesting to the enquirer into the detail of science, but engaging
to the man of general information and cultivated taste.

‘¢ The northern coast of Antrim seems to have been originally a compact body of lime-
stone, (chalk) considerably higher than the present level of the sea; over which, at some
later period, extensive bodies of vitrifiable stone have been superinduced in a state of
softness. The original calcareous stratum appears to be very much deranged and inter-
rupted by these incumbent masses. In some places it is depressed greatly below its an-
cient level. Shortly after it is borne down to the water’s edge, and can be traced
under its surface: by and by it dips entirely, and seems irrecoverably lost under the su«
perior mass. In a short space, however, it begins to emerge, and after a similar variation
recovers its original height.””—Letters on the Coast of Antrim, page 5.

208 The Rev. W. CONYBEARE on

Of this interesting spot it is hoped that the general section, and
the views in Plate 11. fig. 2. will convey an accurate conception.*

* Desiring to keep that description of facts which must serve as the ground-work of
theory, and which seems, in the present state of science, the most useful employment of
the geologist, distinct from conclusions merely speculative, I have hitherto studiously
refrained from expressing the views which I have been Jed to form on the origin of basalt,
and of the other rocks usually associated under the general name of floetz trap.

But while describing the striking appearances presented by Kenbaan cliffs, I cannot

forbear to declare the conviction which this spot first impressed upon my mind, and to
express my full assent to the arguments of those who maintain the igneous origin of such
formations.
' I would observe then that this formation is distinguished by characters so directly op-
posed to those which all rocks undoubtedly of aqueous origin possess, that no hypothesis
which ascribes both to a common origin, can be otherwise than contradictory, and at
variance with itself. For

I. Of all other formations, the least ancient are the least elevated ; but this, the most
recent of all, yet rivals the primitive mountains in height.

2. Of all other formations, the degree of consolidation decreases together with its
age, their texture passing from crystalline through the several gradations of sub-crys-
talline, compact, coarse, and lastly earthy; while in this formation, even where it rests
on chalk, the crystalline texture of the oldest rocks frequently recurs.

3. Whin dykes, which are indisputably connected with this formation, differ from
all other mineral veins, in the circumstance of their traversing all rocks indifferently ;
while of other veins, particular classes are exclusively associated with particular rocks.

Such being the negative evidence against the Neptunian hypothesis, I proceed to that
which is positive in favor of the volcanists ; as

1. ‘The identity of chemical composition in basalt and lava.

2. The constant occurrence of trap rocks in volcanic districts.

=

3. The confession of the Wernerians themselves, that the basalt of Auvergne is of
igneous origin. d

4. The testimony of those best acquainted with districts still exhibiting active vol-
canoes. Such persons, as Dolomieu and Spallanzani, have uniformly maintained the
igneous origin of basalt, while those who have contended against it have generally been
unacquainted with countries of this description.

Having thus alluded to, rather than stated, some of the general arguments on which
this question appears to me to depend, I return to Kenbaan, where the basalt is seen ex-
tending from beneath as well as overlying the great mass of chalk, which has at one
extremity assumed such a curvature as would naturally result from lateral pressure ; and at
the other is rent, and shattered in the most extraordinary manner, the basaltic matter

the North East of Ireland. 209

A-mass of chalk, extending about a furlong in the face of the
cliffs, is here seen, terminated abruptly, and with every appearance of’
violent convulsion at both extremities. Towards the east it is under-
lain as well as overlain by basalt, and loses itself, forming a narrow
tongue surrounded by that rock. in this quarter a portion of the
chalky strata, elsewhere horizontal, exhibits a remarkable curvature.
Towards the west the chalk runs far out to sea, forming a sharp
and narrow point of land, of which the greatest height is about 70
feet. The isthmus which joins this point with the main land, is

insinuating itself into the fissures, and often converting by its contact chalk into granular
marble, while fragments of the chalk, of all sizes, appear to have heen forced upwards
and imbedded in the basaltic rock, having suffered in their superficial parts where the
basalt touches them a most remarkable change.

It seems impossible to conceive appearances more utterly irreconcilable with the hypo-
thesis, that the basalt was deposited regularly above the chalk from a state of aqueous
solution. On the other hand, were we to imagine a priori, the phenomena which would
probably result from the eruption of a current cf ignited lava from beneath the chalk,
and its subsequent diffusion over the upper surface of the chalk, while the whole was
submerged beneath the sea, and under a considerable pressure, they would exactly accord
with those which may actually be observed at Kenbaan.

To the same purpose the changes effected by the whin dykes of this district on the
rocks they traverse might be cited. Thus we have instances : :

1. Of the conversion of cld red sandstone to hornstone. See page 201.

2. Of the conversion of the slate clay of the coal measures to flinty slate, and of the
reduction of the coal itself to cinders. See pages 205, 206.

3. Probably, also, of the conversion of the slate clay of the lias formation into flinty
slate. See page 213.

4. Of the conversion of chalk in several places into granular marble. See pages 172. 173.

Hence, if it be allowable to speculate on subjects so remote from actual observation, I
would infer that the hypothesis which ascribes the formation of the flaetz trap rocks to
submarine volcanoes, which were active at a very remote period before the seas and conti-«
nents had assumed their present relative level, is both in itself more consistent, and in its
application to the actual phenomena more satisfactory than any other.

It is evident that the basaltic mass of Ulster was accumulated antecedently to the last
great convulsion which has modified the surface of our globe, excavating its vallies, and
constituting its alluvial deposits.

VOL. Ill. 2nd

210 The Rev. W. CONYBEARE 02

completely broken through. The ruins of an ancient tower rise above
this chasm, on the sides of which the course of an enormous whin
dyke may be traced; and the whole promontory is shattered in
every direction, masses of basalt (sometimes mingled with chalky
debris and flints) protruding through numerous fissures. The
chalk, where it comes into contact with these dykes, is often con-
verted into a compact and crystalline marble.

The mass of chalk just described is covered by thick beds of ba-
salt; but near the top of the cliffs, which here rise about 300 feet,
are seen two other beds, which viewed from a small distance ap-
pear to be chalk, one rising to the surface above the western, and
the other above the eastern extremity of the inferior chalky mass.
These, on nearer examination, appeared to be a breccia composed of
fragments of chalk, of various sizes, intermixed with flints and ba-
saltic concretions. ‘The outer surfaces of these fragments are much
altered, and they are penetrated by small nests of a greenish sub-
stance appearing to be steatite, the interior presenting the chalk in
its usual state. |

The opposite coast of the island of Rathlin exhibits, as will be
seen by the section of it in Plate 10. an exact analogy to that of
the main land ; and on that point of it lying directly over against
Kenbaan head, a singular combination of dykes occurs, seeming
to be continuations of those which at the latter place appear to
have been attended with such extraordinary disturbances. Here,
within the distance of 90 feet, three dykes may be seen traversing
the chalk, which is converted into a finely granular marble, where
contiguous to the two outer dykes, and through the whole of the
masses included between these and the central one: these dykes are
situated a little to the west of Church bay, they are marked in the sec-
tion Plate 10; and a ground plan, on a larger scale, is added in Pl.
11. fig. 2. representing their appearance as traced upon the beach.

the North East of Ireland. Fil

Carrick~a-rede is the next remarkable headland to Kenbaan.
Between these promontories the chalk twice rises above the level °
of the sea, and as often sinks beneath it; the strata exhibiting
evident marks of dislocation, and either of elevation or subsi-
dence.

,Carrick-a-rede is an insulated crag of rudely prismatic basalt ;
the dangerous rope bridge thrown across to connect it with the
mainland by those engaged in the salmon fishery, has rendered
it celebrated.

Beyond Carrick-a-rede the limestone again rises, is traversed by
some whin dykes and near Sheep island forms a cliff about 100
feet in height. Here a large detached basaltic rock rises close to it
on the beach, appearing to have been brought by subsidence to
the same level, and to a parallel position. The same remark may
be extended to. Sheep island, itself a basaltic mass.

Above these cliffs are seen the lofty basaltic hills of Knocksoghey
and Croaghmore, where are the columnar strata mentioned in page
183; the wood coal described in page 188 also occurs in this
neighbourhood, close to the village of Ballintoy, of which the
spire is seen forming a conspicuous land mark.

The chalk suffers a partial interruption, attended as usual with
dislocation of the strata, near Ballintoy, but again rises to consi-
derable height on the sloping ground which skirts White Park bay.
In a valley near Ballintoy, the inferior limit of the chalk is ex-
posed, and a substratum of a bluish slate clay, containing gry-
phites and ammonites, (apparently the same which alternates with
the lias near Glenarm) is laid open. ‘The chalk is abruptly broken
off on the east of White Park bay, in a little cove called Port
Braddin. Here the basalt abuts directly against the chalk, and
that arrangement of strata, so well known as constituting the mag-

202

—

912 The Rev. W. CONYBEARE on

nificent range of promontories in the neighbourhood of the Giant’s
Causeway, commences. Since the chalk, which is here placed on
the same level with the highest of these strata, must certainly in
its regular place occur beneath the lowest, and since the whole series
has been ascertained considerably to exceed 400 feet in thickness,
the subsidence of the basaltic mass at this point must have been
very great.

The neighbourhood of the causeway, with all its remarkable
features, its superb storied facades, distinguished by a double order
of columns, its whin dykes and its caverns, have been so fully and
ably described by Dr. Richardson in the Philosophical ‘Transactions,
that they are already familiar to every reader interested in such
subjects. His list of the strata here ascertained has been already
given, page 177. On the strand near the mouth of the Bush, are
two parallel ledges of chalk and basalt.

The appearances of the cliffs between Bushfoot Strand and
Portrush Strand, are so similar to those which we have already.
found frequent occasion to notice, that this part of the section does
not appear to require further elucidation. Near the termination of
the chalk cliff on the west, a very inexplicable phenomenon pre-
sents itself; a large spherical mass of basalt, appearing to be com-
pletely enveloped in the chalk.

The singular peninsula of Portrush demands more particular at-
tention; a long line of strand separates it on either side from the
cliffs which rise at about the distance of a mile to the east and
west.

The peninsula itself, which may be about-a mile in circum-
ference, is fenced with low cliffs on the west, north, and east ;
those on the west present a rudely prismatic greenstone ; those on
the north and east tabular masses of greenstone, overlying, and in

the North East of Ireland. AS

some places appearing to alternate with, a very remarkable rock
which has been the subject of much discussion among the sup- -
porters of opposite theories.

It is a flinty slate, exactly similar to the indurated slate clay
which forms the wall of the Carrick Mawr dyke, in the Ballycastle
collieries ; and the analogy is rendered the more striking, from the
futther resemblance of the greenstone of that dyke to the green-
stone of these cliffs. In this flinty slate are contained numerous
impressions of cornua ammonis invested with pyrites, the shells
being similar to those found in the slate clay underlying the chalk
near Ballintoy.

The advocates of the Neptunian theory consider this rock as a
variety of basalt, and refer triumphantly to its included fossils, as
affording a conclusive argument against the Volcanists.

Professor Playfair, on the other hand, expresses his belief that
“the rock containing the shells is the schistus or stratified stone,
which serves as the base of the basaltes, and which has acquired an
high degree of induration by the vicinity of the great ignited mass
of whinstone.” See illustrations of the Huttonian theory.

The resemblance of this rock to the indurated slate-clay of Car-
rickmawr, and the identity of its fossils with those of the slate. clay
underlying the chalk near Ballintoy, together with the relative po-
sition of Portrush and of the chalky cliffson the east, appeared to us
to give the greatest weight to this very ingenious conjecture; and
we felt convinced while examining the spot, that the rock was no
other than the slate-clay of the lias formation in an indurated state.

The remaining portion of the section will sufficiently explain
itself: it terminates where the secondary formations turning to the
south finally quit the coast. The headland of Macgilligan, the most
northern point of the mountain range formed by their escarpment

914 The Rev. W. CONYBEARE on

in the west of Derry, is seen at the distance of three miles inland ;
it is remarkable for the grandeur of the scenery presented by its
shattered precipices.

Of the island of Rathlin or Raghery, the section represents only
the cliffs extending from its most westerly promontory to the centre
of its southern line of coast. From the point where the section ter-
minates, the precipices round the southern cape and the eastern and
northern shores are exclusively composed of basalt, and frequently
present columnar groups. (See page 182.)

To the conjecture of Dr. Berger, however, that sandstone and
older rocks exist at no great depth in the south-eastern quarter of
the island. (See page 151.) the positive assertion of Mr, Hamilton
must be considered as adding great weight. ‘ An heterogeneous
mass of freestone, coals, iron ore, &c. which forms the east side of
Ballycastle Bay, and appears quite different from the common fossils
of the country, may be traced also directly opposite running under
Raghery, with circumstances which almost demonstrably ascertain
them to be the same veins.”’ Letters on the coast of Antrim, page 8.

From the exact correspondence in structure between the opposite
points of coast upon this island and the main, Mr. H. infers that
‘“‘ Raghery standing as it were in the midst between this and the
Scottish coast may be the surviving fragment of a large tract of
country, which at some period of time has been buried in the
deep.”

The pebbies of sienite which are scattered over various parts of
this island, and must have travelled hither from Cushleak, concur to
prove the later formation of the channel now separating it from the
mainland. Dr. Mac Culloch observed appearances analogous to
these in the island of Staffa, and deduces from them the same con-
clusion. See Transactions of the Geological Society, Vol. I.
page 207.

the North East of Ireland. 215

The facts stated in the introduction to this paper (see pages 123,
125.) are of sucha nature as leave no doubt in the mind of the -
writer, of the former continuity of the Irish and Scotch coasts.

The greatest depth of the channel between Rathlin and Antrim
is 53 fathoms, and between the north-east of Ireland and south-
west of Scotland 90 fathoms.

‘It now only remains to explain the principles followed in the con-
struction of the geological maps accompanying this paper.

The larger of these comprehends the whole of the district which
has been described, as itis limited, in the Introduction, page 121.

Much attention has been bestowed on the delineation of the
mountain chains; the heights of the principal summits are in-
serted from Dr. Berger’s measurements.

The more important soundings on the coast are added.

In a map on so small a scale it was not found practicable to
distinguish every minute formation by different colours; it be-
‘came therefore necessary to assume as the basis of the colouring,
the prevailing rocks which, in association with other subordinate
formations, constitute districts of considerable extent.

Thus the districts to which separate colours have been assigned,
are

1. The granitic district of the Mourne mountains, &c. The
hornblende or primitive trap rocks, on the border of this district,
are distinguished by an appropriate mark.

2. The mica slate districts of Londonderry and Antrim, including
primitive limestone, felspar, porphyry, and sienite, each distin-
guished by peculiar signs.

3. The transition district, encircling the Mourne mountains.
The lead mines in this district are marked.

4, The shell limestone underlying the coal.

216 The Rev. W. ConyBeare™ on the North East of Ireland.

5. The sandstone district, of which the lower beds are associated
with the coal, and the upper with gypsum. The collieries are distin-
guished by black circles.

6. ‘The zone formed by the basset of the chalk round the escarp-
ments of the mountain groupe, which forms our third system. It
was not possible to insert the lias and greensand intervening between
the sandstone and chalk ; but their localities are fully indicated in the
paper and in the sections.

7. The great district of floetz trap.

The smaller map, Pl. 9, exhibits a general outline of the opposite
points of Scotland and Ireland, intended to shew the connection be-
tween the principal formations in each country, as pointed out in the
Introduction. The colours represent.—1. Granite. 2, The mica
slate district of the Grampians, and the northern chain in Ireland. 3.
The transition district of the Lead hills in Scotland, and of Down in
Ireland. 4. The secondary rocks associated in the coal district.
5. The floetz trap districts.

ELEVATIONS OF SEVERAL STATIONS

IN THE COUNTIES OF

LOUTH, ARMAGH, DOWN, ANTRIM, AND LONDONDERRY,

Calculated from the Level of the Sea by Barometrical Measurement,

By Dr. BERGER,

County of Louth.

Highest part of the road between Dundalk and
Newry, by Jonesborough

Barensdale mountains, . highest part of Lower
Dundalk Barony

Foy mountain; the highest of the Carlingford
mountains . .

Golding mountain ; Mountain town ? ? ‘lower ridge
of Carlingford mountains, (Copley. mountain of
M’ Kenzie ?) : ;

County of Armagh.

FEET.
1 Fathom mountains; the highest aes of, along
the Newry River . . 820
2 Cum-Lough ; between Slieve- Gullen ‘and Slieve-
Girkin, or Newry mountains 305
3 Killevy or Kilsleve-Church, at the base of Slieve-
Gullen, on the south-side ; 5034
4 Slieve-Gullen 1900
5 Slieve-Girkin or Newry mountains 1340
6 Faughell or Foughall mountains, a little te the
north-east of Jonesborough : : 822!

Won, Iii. 2s

218 Dr. BERGER oa the Geological Features

COUNTY OF DOWN.

MOURNE MOUNTAINS.

+ LOWER IVEAGH.

1 Rosstrerve-hill, at a large block of aoe not
quite tothe top of the hill. °

2 Lough-Sally? at the entrance of a peaty circus
(Deer’s Meadow?) situated at the foot of the
Mourne mountains to thesouth . :
Lough Shannagh; on the ers of Slieve Muck :
Slieve Muck . ° >
Slieve Snaven (Slieve Birna Phy : 5 3
Bingan mountain (Brem Buncin?) . ° .
Slieve Donard ; .

Newcastle Slate quarry; on the acclivity and
towards the base of Slieve Donard 3 :
Dundrum Jead-mines 2 : ‘ :

© ONTO & mm OO

++ UPPER IVEAGH.

i0 Clark-hill, Slieve Slut? within (referred to Cas-
tlewellan) the demesne of the Earl of An-
nesley . . : . .

11 Slieve Anisky .

12 Bakaderry town, near a cross bearing the date
Lara, ° . ° . . . .

Slieve Croob . ae : ‘ 4 . z

ttt ARbs.

Temple of the winds ; Mount Stewart .

15 Captain Allen’s fort, (Black Abbey?) one of the
highest spots across the peninsula of Ards,
near B. Atwood . - ° 3 . 2
16 Windmill of B. Neboly . . . .

Conlig-hill Bangor - 4 : .

++++ CASTLEREAGH.

Scrabo-hill .

19 The watershed between Strangford-Lough or i
Cone and Belfast Taare not far from Kirk

Donnel . . - . -

the North East of Ireland.

COUNTY OF ANTRIM.

Dirris mountain, Belfast

Doon ravine, oer Allan’s Ravine, upper’ part,
Belfast

Cave hill, Belfast, upper line of the white times
stone . . :

Mc Arth Forth : Gac-kul Ga © - :

Thickness of the cap oftrap . : :

Squire’s-hill, Belfast te -

Rumbling-hole, upper part of, Collin’ s Glen .

Black Mountains ; Belfast ;

Watershed. of the road between Belfast and An-
trim. .

Ditto, referred to Lough Neagh .

Hence elevation of Lough Neagh :

Glenery Church, referred to Lough Neagh -

The same referred to the sea; iii preainet
tical) . :

Dramadaraghy! or Ballyroy-hill, " above Doagh

Sandy Brae hill, above Doagh . : c .

Slemish Mountain, above Broughshane

Carnybuy ? highest part of the road between
Coleraine and Bushmills : .

Cliff by Dunluce-castle . : :

Orbilt ? (Dunmull top)

Cape Pleaskin: from two observations

Bengore-head, from two observations :

Clogher ; alittle to the north-east of Bushmills .

Craig-park, to the south east of Bushmills .

Ballychra-crafey : townland of TTR OO,

Cliff (of chalk) facing Sheep island

Croaghmore, near Ballintoy

Cross-hill, (B. Castle aay upper line of
the freestone °

Cross-hill, top °

Thickness of the cap of trap

Fairhead top

Murloch, upper line ‘of the red freestone

Murloch, limestone cliff

Benvaan top, near Murloch

Coolnagopag, or Carnanmore, near Murloch, from
two observations .

Knocklead top

Cloughamurry town- Leal an aecity of Knock
lead, upper apparent limit of the granular and
micaceous limestone

Cape Castle: on an neolivitgs of Kntsltleasbc

upper apparent limit of the white limestone

Ze 2

220 Dr. BERGER on the Geological Features

COUNTY OF ANTRIM.
| 35 Ballydurnian: on the acclivity of Knocklead:
upper apparent limit of the white limestone
36 | Munnanacloick, on the acclivity of Knocklead ;
upper apparent limit of the white limestone . 920
(37 B. Patrick, upper line of the white limestone. 622
238 B. Patrick, top : 955
39 Breen, a swampy ground, main feeder of the
bush R. ° 5 . : 7621
40 Ardagh : level of the Ciitiesk R. 797
Al Highest part of the old road between B. Castle
4 and Cushendun . 945
42 | Middle Cushleak: lower = of the white limes
stone: . ° “ ° . ‘ . 695
43 Doon-a-rary Castle < 9 236
44 Qona, habitations in the valley of Glendun : 590
45 Beagh habitations, Glendun valley . : : 3674
46 Beagh mor 974
A7 Glendun ; sala apparent limit of the white lime-
stone . . . * . . . 885
48 Slieve-Nory, top . : 1530
49 Upper limit of the white ceca ie Aghan,.
Oona mountain. 8821
50 Teabulliagh : upper line of the white ‘Timentotie é 735
51 Teabulliagh mountain top é : 1235
52 Cliff above the caves of Cushendun, oalled Cra-
nagh . . . ° 1231
53 Teavuagh; by Cushendall ‘Church | ;. 522
54 Slieve-Cross ; highest ground between Cushen-
dun and Cushendall, on the right of the road . 7421
55 Highest part of the Shore-road, between -Cush-
endun and Cushendall . : 610
56 Craig Rammer mountain; a little to the noi
west of Cushendall ° : ; : é 559

+ ISLE OF RATHLIN, OF RAGHERY,.

57 Slieve Ard < - : - 3 ; : 3724
58 Cligan Lough . : : : = : : 238

59 Kinrammer-head. E wth. 48 2 3 3524
60 Bull-point 7 ‘ zs : - = 280

61 Sliebh-an-all . é A 5 : é 3474
62 Kintwan-head . : : Fay Wee : j 3182
63 Altahorry point = : : : ‘ : 834
64 Crook-a-harnane . . 3 s F ; 1044
65 Ushet Lough . é : “ es 144%
66 Drimnagrulligh 3 : ° . Z : 2283
67 Broagh-mor-na-hoosid . - 3 2344
68 Slieve- -na-varagin (the rocky-hill 4) uses . ; 934

69 Slack-na Calye Cliff ; : : : 240

of the North East of Ireland.

COUNTY OF LONDONDERRY.

Moneymore . dH " : , : :

Mayola R. wiide 4 nearly half way between
Cookstown and Dungiven

Highest part of the road from the bridge ¢ on the
Mayola R.to Dungiven-

Cragnashoack-hill (the Hawk’s “hit $ the - ‘upper
line of the sandstone.

Cragnashoack mountain: top.

Dungiven .

The three following heights were directly
referred to Dungiven, and thence calculated
above the level of the sea.

Benbradagh-hill; upper line of the sandstone.

Benbradagh-hill; upper line of the white lime-
stone . . . . . . °

Benbradagh top z

The Glebe-house of Garvagh

The eight following heights have been
‘ referred directly to this spot, and thence calcu-
lated above the sea.

Broka-bhoy : a swell of Spee the on the hoes
of Coolcoscrehan mountain c

Coolcoscrehan mountain top

Dunavenny brook; a feeder of Allen water,
being the first appearance of the primitive for-
mation on the slope of Cairntogher

Cairntogher mountain top

A swampy ground on the south side of Cairn-
togher; the head of several rivers .

Donald hill: upper line of the sandstone

Donald hill top 4 - 2 _

Ballyness limestone quarry : upper line of the
limestone : . : .

Down-hill : iausol@um of the late Lord Bristol.

Benyavenagh mountain towards Magilligan point,
a complete mass of stratified trap. (rating the
limestone at 80 feet.) . 5

Cady-hill; upper line of the white limestone

Cady-hill top . :

Watershead of the road between Coleraine and
Newtown-Limavaddy

221

222

Dr. BERGER on the Geological Features, &&c.

COUNTY OF LONDONDERRY.

Many of the following mountains belong
to the county of Tyrone, as well as to that of
Londonderry ; since they limit the two counties.

Banagher Church. ° 7 . .

Mullaghash mountain top . . . .

Sawell mountain top

Knocken Bann ; Monterloney : "the highest cul-
tivated ground I have seen in the North of
Ireland. Crop of oats * :

Fin-Glen or Fion-Glen mountain top + z

Moneynieny ; the mountain of wonders’. .

Sphell-Cooagh: the Cuckoo’s mountain

Dunlogan-hill; an appendage to Sphell- Cooagh .

Ben-Bhoy .

Ch. o’Hagan’s Inn: from Mayola bridge to Dun-
given

Lough Faé or Fi inea; on the west side of Slieve
Gallion mountain .

Highest ground on the road between Cookstown
and the Mayola bridge . : .

Upper line of the limestone on Slieve Gallion .

Tamach ; highest part of; Slieve Gallion . .

The thickness of the limestone formation is but
very inconsiderable

Cumber-Clady: Mr. James Ross’ house: Faug-

han valley : from two observations : .
Lesstress-hill; by the waterfall of Ness
Malabwea-hill . » » . :

FEET.

* 'They were ripe, and some had already been cut on the 20th September, 1811.

+ This and the five following heights were referred, as before, diractly to Dungiven.

IV. Ox the Dykes of the North of Ireland.
By J. F. Bercer, M.D. Member of the Geological Society.

Read November 4th, 1814.

/

My object in the following paper is to describe some of the
more general characters of Dykes, such as I have lately observed
them in the North of Ireland.

I do not know exactly within what geographical limits these
curious geological phenomena are to be met with: they are com-
mon on the Western coast and in the Isles of Scotland, and I have
observed them also in the Isle of Man. I understand that none
have yet been remarked in the South of Ireland, and I did not
observe any in the Midland counties through which I passed be-
tween Dublin and the Northern coast. In England they have
been found in the centre of the island, as at the colliery of Tividale
in Staffordshire ; but in the North of Ireland it is only on the verge
of the coast that they abound, and it is there that I have principally
examined them. Of more than sixty that I noticed, nearly half
were situated on the shore; those which occur in the mountains
of Donegal are I believe the remotest from the sea, and those lie
within fifteen miles of it.

I have not found their occurrence to depend upon the absolute
elevation of the country in which they appear. I have observed
them at almost every altitude between that of the shore and those
which I have inserted in the following Table, as being the greatest
and somewhat uncommon.

224 Dr. BERGER on the Dykes

Feet
i. Dyke on Cave-hill, West of Belfast Lough on the Antrim side, above the sea 1064
2. Ditto on the top of Ballyghuia Cupola, Kilmacrenan, Donegal . . . . . 1448

3. Ditto near the top of Aghla mor, Boylagh, Donegal . ~ ~ - «© « « « 1726
4. Ditto near the top of Glendoan, Kilmacrenan, Donegal . . . . «. « ~« 1738
5. Ditto on the top of Glencarn mountain, Boylagh, Donegal . . . st og Maras
6. Ditto near the top of Arragh, the highest mountain in Donegal N.W. side - . 1848
FA TDstto 5.) 8s. 3S SOR ee 2) oo. re om eae a Se

It seldom happens in the North of Ireland that dykes occur
singly ; but they are generally found in groups, several within a
short distance of-one another. Thus, at the Giant’s Causeway
there are 6 within 2 English miles; at the collieries of Ballycastle
5 within the same distance ; at Alt-a-dora (a glen in the valley of
Dunlughy) 4 within 1 mile; on the N. W. side of Arragh, 6
within 1042 feet ; and at Church home in the basin of Dunlughy,
4 within 835 feet.

The uniform direction or parallelism of nearly all the dykes in
the North of Ireland is a curious circumstance resulting from my
observations: I have subjoined a list of all the dykes that I sur-
veyed with accuracy, in order to put the Society in possession of
the data from which I have drawn this conclusion. Many of those
in the table were surveyed with a theodolite, others with a very
good pocket compass mounted on agate; in all the latter cases I
have allowed for a variation of 29° West, upon the authority of
Mr. Hanton of Loch-beg in the Rosses, who made two observations
at my request in order to determine the point. I have rejected
from this table the bearings of all the dykes, which I observed with
only a common pocket compass, as not having any pretensions to
accuracy; and among these the bearings of the famous dykes of
the Giant’s Causeway ; had all however been admitted, they would
all have tended to establish the above-mentioned conclusion.*

* The direction of the two dykes at the colliery of Tividale in Staffordshire, is also from ~
$.E. to N.W.

of the North of Ireland. 925

Angle at

Direction Direction | which the
Locality of the Dyke Stratum traversed of stratam
W. of N. E. of N.

1 |Far-Dunlughy, Donegal .} 21° [Primitive blue limestone
2 |Church-home Dunlughy, 17° Gneiss and primitive
Donegal . . .- : granular limestone

Sia e ee ae Ts
SiO PRON fF BIG) OQ7S TO Re- SiISV GH sage
5 |Ditto . . ME a) ewe Sere
6 Mein-a-bole, N.W. deat 71
7
8
9

51°
552°

Arragh, Donegal Bluish white limestone

Ditto B tke ve 38 s :
WO aw cla ieineel choo ne 48 . ee oe ne
WTHELOPT a8 ahs ere 37 ss tes tthe Ghee ee
LocdiDittosacss A 2m. Gioia. 63 of totte By them Sek
Me ee Poe Th eee ce ee ne kes
TSC DittoHt,.«. tee AO09LG 44 2
US UWNEEOus Wes ea ee ay es A6
PA DEO Syme ve sens. tbe: SB Ad

15 |Ditto F if es te an a Be
16 ‘Alt-na-Calge Dunloghy | 31 |Talcose limestone .
17. A DittO, [61 2 ops - 312 j. . . tic
18 |Ditto . . Yo ee Piss

19 Bouilech Pointy Isle of ' 20 |Sienite
rran-mor, Donegal

20 |Pool-a-Phuca, Church-hill, Bs Limestone with Gaare:

Fermanagh ; lesser dyke pores...

South limb a4 4

21 |Ditto, North limb 31 Sy a | Br ae te, . 120
22 |Ditto, great dyke 35 sets | Soren 2 124
28, |Lough-na-Croey, Stranag- t 49 |Primitive limestone .| 41 90
logh mountain, Donegal
24 |Dunbeg, Giddore, Donegal] 19 |Sienite
25 |Aghla-mor, Boylagh 39 = |Slaty quartz . 71 110
26 |Trayenagh Bay, Rosses 19 —|Sienite
27 |Ditto cla: | 24 {Ditto
28 |Lough Foyle, between’
White and Red Castle ef 49 Sandstone ..-+. .« 16 65

SROs oe Ys | 41 |Porphyritic sienite
30f(Ditto-scrfe Fy slilepue oy 18
Ditto ‘

VOL, Ill. >A

226 Dr, BerGER ou the Dykes

The conclusion to be drawn from this table is that the bearing
of the dykes is from S. E. to N. W., and that the dykes all cut the
planes of the strata through which they pass, at very considerable
angles. ;

A shift in the direction of a dyke is an accident of rare occur-
rence; it would probably however be more frequently observed,
did not the soil, which covers the surface, prevent us from tracing
the dyke to any distance.

The most considerable shift that I ever observed was at Rannagh
Point in the Isle of Arran-mor, where it was not less than 47° in
126 feet. At Muir-a-Bole on the N.W. side of Arragh, I ob-
served two other considerable shifts; the one of 22°, the other
of 27°. .

Dykes differ greatly from one another in their widths, which
measure from a few inches to several hundred feet. The latter
dimensions are of rare occurrence, and I have only met with three
cases of the kind, all in secondary strata; and in two of these the
enlargement took place at the bottom of the dyke. One is found
in the red bay of Cushendall; the other at Pool-a-Phuca in the
county of Fermanagh. The third case occurs between Portrush
and Dunbar Castle on the coast of Antrim, and has been noticed.
by Dr. Richardson. I think I have ascertained that there is a»
remarkable difference in the average widths of the dykes, according
as they are found in primitive or secondary rocks. Out of sixty-
two dykes that I have measured, the average width of thirty-eight
in the primitive districts is 9 feet; that of twenty-four in the
secondary is 24 feet.

I have already noticed some of the more remarkable elevations
at which dykes have been found. The height to which a dyke
rises above the surface of the stratum, which it intersects, is some-

of the North of Ireland. 227

times very considerable. ‘That on the N.W. side of Arragh rises
perpendicularly 40 feet, like a partition wall; that on the cupola of .
Bally-ghuia 8 or 10 feet ; at Scrabo Hill near Newtown Ards in
the county of Down a dyke appears like a standing pillar at the
entrance of one of the freestone quarries. The dyke of Port-na-
brock near the Giant’s Causeway, juts out into the sea quite iso-
lated to the visible extent of 372 feet. On the contrary, those on
the summits of Glendoun, Glencarn, and Aghla-mor, appear like
strewed masses, scattered about upon the surface. These might be
adduced as instances to prove the wearing away of mountains, =
that point stood in need of any additional confirmation.

The depth to which the dykes descend is unknown; and after
having observed the sections of a great many along the coast in
cliffs from 50 to 400 feet in height, I have not been able to ascer-
tain (except in one or two cases) that their sides converge or have
a wedgeform tendency ; so that no estimate can be formed of the
_depth at which they terminate. In this respect therefore they do
not seem to agree with the metallic veins.

Moreover, I have not observed that they branch off into slender
strings, or (except in some very rare instances) that they swell into
(what the miners term) bellies, after the manner of the metallic
veins. |

The dykes, whether they occur in primitive or secondary coun-
tries are nearly vertical. The mean angle of deviation from the
perpendicular deduced from nine cases occurting in primitive rocks
was 13°, the extremes being 9° and 20°. The same angle deduced
from ten other cases was 7° to the N.E. But Iam not warranted
in drawing any general conclusion as to what point of the compass
and in what degree they deviate. The angle of deviation in the
two remarkable dykes on Arragh mountain is somewhat consider-

ZF 2

228 Dr. BERGER on the Dykes

able, as is also that of the dyke in the quarries of Scrabo hill; but
I am nat able to state it with precision.

There is net that variety in the substance of the dykes, that
their numbers, their distance from one another, and the varied
nature of the rocks which they intersect would lead one to expect.
I have found them composed of the following rocks, which are
introduced in the order of their most frequent occurrence. Trap
and greenstone, with their associates Lydian stone, flinty slate,
greystone and wacke.

I have seen but one dyke of clay porphyry, viz. at Farland point
in Donegal, and I conceive it to be altogether of a different class
from those dykes to which my principal attention has been given
in the present paper.

A dyke is formed either of a number of diminutive pillars aggre-
gated together, or of square rhomboidal pieces piled one upon
another like blocks of masonry, the long axes of these figures in
either case lying transverse, and perpendicular to the walls of the
dyke. These regular figures are often much disintegrated and
rounded, and sometimes assume the coated form; the two appear-
ances being often united in the same portion of rock.

Dykes are not, like metallic veins, divided into regular layers of
different stony substances; nor do we find in them those drusy
cavities which sometimes occupy the middle of metallic veins.

The more compact the trap, the more apt is it to assume the
polyhedral form, to be homogeneous, and to be free from the por-
phyritic texture. In the hard variety I never found imbedded any
detached mineral concretions, except a few small specks of soft
green steatite. When less compact, it is often set more or less
thickly with heterogeneous nodules, but seldom so abundantly as to

of the North of Ireland. 229

assume a texture decidedly porphyritic. Among these nodules I
have found the following minerals.

Minerals found imbedded in Dykes. , Locality.

Augite in angular fragments . . «| Isle-of Islandowey.
Olivine in disseminated grains . . | GlenofAlt-a-darain the valley of Dunlughy
Crystallized glassy felspar . . . | Glen of Alt-a-dara.
Compact felspar in distinct rounded
concretions.

Radiated zeolite ered ial we N.W. side of Arragh, highest dyke but one.

Green soft steatite, in distinct con-
cretions.
Tron pyrites.
Calcareous spar. i
Carbonate of lime, mixed with the { On the shore on the Antrim side of Belfast

raps S946 Sit 1 -oeO. ws : Lough.
Glassy quartz in distinct concretions.
Sulphate of barytes.

Plates of mica.

The mean specific gravity of the trap rocks forming dykes may
be rated at about 2.86. That of the specimens from Alt-a-dara,
containing olivine, being 3.14; that of homogeneous trap from the
dykes of the Giant’s Causeway being 2.99; and that of the wacke
from the shore at Carrick-fergus being 2.45.

The dykes are found traversing both the primitive and the
secondary rocks, nor have I ascertained in which they are the most
frequent. There appears to be no regular connexion between the
substance of the dyke and the rock through which it passes. I have
however sometimes found lime in considerable quantity in the dykes
that traverse limestone. Glassy felspar I have only found in the
dykes of primitive rocks.

In the table of the observations of the dykes some of the rocks
cut by them are enumerated; I have added however another table

230 Dr. BERGER on the Dykes

of the rocks that I have seen intersected, with some additional

localities.

Rocks cut by Dykes. Localities.

Primitive limestone . . . . . ~ | Vide former list.
SICHHTC 5 + o. o nfarle Newry, Bloody Farland, &c.

Slaty quartz . . . . . . « «| Farland point, Donegal.

Micaslate. . . . . . + « «4 Kildrim Jead mine in Donegal.

MGHEIES aero ee) cee sm see tee el te

Transition limestone* . . . . . | Blockhouse Isle, entrance of Carlingford bay.

Old red sandstone . . . . . «| Near Newton Glens.

Floetz limestone alternating with

sandstone and underlying the coal. | East of Bally-castle.

Coal measures. . . - - ~ ~ «| East of Bally-castle.

Chalk . . ... =... ~~ « 4} East of Glenarm, where the limestone is ren-
dered hard and crystalline in contact with
the dykes. One of the dykes branches and
encloses portions of the limestone, and
many other places, see page 172.

Flotz trap, basaltt . . . . ~ «~ | Giant’s Causeway, and many other places.

The induration which the secondary rocks undergo when tra-
versed by dykes has often been noticed; it is not my intention now
to discuss this subject ; I shall only mention that the induration does
not extend far from the dyke, and that the phenomena though very
frequent are not universal.{ I have only noticed one instance of
remarkable change in a primitive rock contiguous to a dyke. In
the case I allude to, viz. in the lead mine of Kildrim in the county
of Donegal, mica slate adjacent to the dyke had its texture quite
loosened, and was in a dusty state.

* A dyke also traverses transition limestone, containing magnesian limestone, at Scarlet
point in the Isle of Man. + Inserted by the Editor.

+ The white limestone when thus indurated becomes, as is well known, phosphorescent.
T have found limestone, accompanying the undoubted lavas of Andernach in the Palatinate,
and containing garnets and augite, not to possess this property.

of the North of Ireland. 231

In general there is no foreign matter between the substance of
the dyke and the rock it divides, excepting a slight rusty appearance
on the surface of the latter. The contact between the two is
pretty close, but they may always be disjoined by the blow of a
hammer. When the dyke is prismatic, a hollow interval between
the two may sometimes be observed.

Since the average direction of the dykes is from south-east
to north-west, and since the average dip of the strata in the north
of Ireland is to the south-east, it will follow (independently of the
several observations on the bearings of the strata contained in the
table) that the direction of the dykes is nearly perpendicular to that
of the strata.

Moreover since the longitudinal vallies and the metallic veins of
a district are generally parallel to one another, and to the direction
of the strata which they intersect, it will follow that the dykes will
cross the longitudinal vallies, and that where metalliferous veins
and dykes occur together, that one of the two will cut the other.
This is the case at the lead mine of Kildrim in Donegal, where the
dyke divides the vein. Similar facts are recounted in the Philoso-
phical Transactions, 1790, page 93, by Mr. Mills,* as occurring at
the lead mines of Persabus and Glasgow-beg in the isle of Ilay ;
where although the directions of the dykes are not uniform, as in
the north of Ireland, yet they cut the veins nearly at right angles,

a

* M. Brongniart as well. as Dr. Richardson from whom he quotes, (Irish Trans. Vol. 9,
page 22,) appears to have misunderstood this passage, and adduces it to proye that dykes
are traversed by lead veins, the reverse being the case : Traité de Mineralogie, tom. 1. p. 462.
He also quotes some observations said to be made by M. Humboldt on the basalt of
Unkeln, from Journal des Mines, No. 19, p. 378, to prove that dykes are sometimes
metalliferous ; but it does not appear on referring to that number that dykes are there
spoken of, nor indeed does the reporter appear to have been satisfied with the expression
“ raies metalliques,”” or to have relied much on the accuracy of the observations.

232 Dr. BERGER on the Dykes

It is very evident from these observations that some of the dykes
at least were formed at a later period than the metallic veins; an
inference that might be extended to all, could we show them to
be all cotemporaneous. That they are so is rendered probable by
their parallelism, and by the nearly uniform texture of the trap,
in whatever rock the dyke is found. The simple minerals too
contained in the trap favour this opinion. Calcareous and heavy
spar, and lime intimately mixed with the trap abound most in the
dykes of secondary rocks; iron pyrites is common to those both of
primitive and secondary districts; and radiated zeolite, olivine and
augite are common to the dykes of primitive rocks and to the beds
of trap of secondary formation. -

From this inference, however, I must except a class of dykes
which run parallel to the metallic veins, and are probably inter-
sected by that class of dykes which I have been describing in the
present paper. An example of this new class of dykes is found at
Farland point in the county of Donegal, where alternating strata of
slaty quartz and sienite are traversed by a dyke of clay porphyry
bearing east of north 21°: a dyke of trap is found at the same place
bearing west of north 49°, the angle between the two being 100°.
There can be no doubt that they meet one another, but the spot
being covered by the sea, I could not discover the point of inter-
section.

Whatever date and whatever agents we are disposed to assign to
the origin of dykes, their uniformly. vertical and nearly parallel
positions evince that both they and the mountains which they
intersect have not undergone any modern disturbance beyond super-
ficial abrasion, but that they remain in the same situation as at the
remote period at which they were formed.

of the North of Ireland. 233

APPENDIX.

On the Dykes of Monte Somma, in Italy,
Extracted from a Series of Letters addressed to the late

LORD CHARLEMONT, P.R.I.A.

By the late Rey. GEORGE GRAYDON, Fellow of Trinity College Dublin.
Dated Naples.

“« THE appearance of the face of the cliff of Monte Somma in its
whole length perfectly coincides with the idea given by its semi-
circular shape, surrounding Vesuvius, as well as by its sloping back
as seen from Naples, and strongly confirnis the opinion of its
having once formed a much higher conical hill.”

“The face of the cliff viewed on a horizontal line is by no means
smooth, but considerably indented in some places into semicircular
or more than semicircular hollows or recesses, with sides nearly
perpendicular; in others into hollows with steep sloping sides
down which the sand and stones are continually sliding.”

“It is formed of a great number of successive strata of lavas, in some
places perhaps upwards of thirty ; these strata in general are thin,
that is, not exceeding from three to six feet in depth of solid stone,
the intervals between them, which are generally much thicker than
the strata themselves, consist of porous red or calcined and usually

* This gentleman presented a series of volcanic specimens, collected by himself on
Vesuvius, to the Royal Irish Academy; vide Kirwan’s Mineralogy, ed. 1794, vol. 1.
preface, page xv, where he is much commended.

VOL. Ill. 2G

234 Dr. BERGER on the Dykes

loese roundish stones, properly scoriz, superincumbent on the
respective strata of lava, and belonging to each; but I did not
observe any stratum of vegetable mould, properly so called, though
I believe there may be some puzzolana and rapilli.”

“The strata are intersected in many places by walls generally
perpendicular to the face of the bank as well as to the direction of
the strata, in others inclined somewhat to the latter, and in some to
both, and often small ones branching off from the greater perpen-
dicular ones, and inclined to them low down in the substance of
the hill itself. ‘These seem evidently to have been fissures or
cracks of the whole crust of the hill from top to bottom, into
which the lava had flowed and filled them. The lava of which
these are composed differs also in the same manner as that of the
strata: in some it is compact and almost homogeneous, in which
case the joints into which it is divided generally lie across its
direction, that is, are nearly horizontal ; and it is divided into ir-
regular polygonal parts, in some places assuming a very rude sketch
of basaltic columnization; in others it is porous and heterogeneous,
particularly in such as are formed of the granitical lava, have a red
scorified appearance and an irregularly globular structure.

** The remarkable analogy between the several circumstances of
the face of Somma and of the cliffs of the county of Antrim in ,
Ireland from Bengore head to the river Bush, must strike any one
. that has seen both. The principal differences between the two are,
the constant uniformity of the Antrim strata, the homogeneity of
their matter, their basaltic form, andthe much greater depth of the
strata, which are seldom less than twenty-five or thirty feet, and
the less rapid inclination inwards of the strata, which there seems
not to exceed an angle of fifteen or twenty degrees, whereas here
mm Somma the angle is not less than from forty to forty-five degrees,

of the North of Ireland. 235

which in both amounts nearly to the angle of the dip of the outward
surface of the hill which they compose.”

“ These differences seem to have resulted from the greater vicinity
of the cliffs at Somma to the seat of the crater as well as to the
more rapid slope of the hill, which from the greater degree of
fluidity of the lavas, and their more rapid tendency to descend, did
not allow them to acquire there any considerable thickness ; whereas
in Antrim the distance being probably greater from the crater, and
the slope much less, the lavas could settle there in greater depth.
The basaltic walls also found along the coast of Antrim, and parti-
cularly of Ballycastle and Belfast, seem to have a perfect analogy
with those of Somma, but are of much greater breadth in general,
and the intervening strata of porous and irregular basaltic matter
between them correspond exactly with those of scoriz in all lavas,
and so visible in the ancient ones of Somma.”

“ Tn the side of one of these walls of Somma, I found a crust of
completely vitrified matter, covering a schistose cracked and very
fragile homogeneous lava, disposed, contrary to the general rule of
that kind, in perpendicular joints, and much resembling a kind of
schistose hornstone, as well as the upper and superficial covering of
Pleaskin.”

“The whole of the valley between Somma and Vesuvius is
covered with repeated irruptions of lava, particularly those of 1767,
1779, and 1787, which have run to the foot of the rock and
to a considerable depth.”

This description will be found to agree pretty well with that of
M. Breislack (Voyages dans la Campanie. tom. 1. p. 133. Paris
1801.) ; from both of which it is sufficiently clear, that the walls of
Monte Somma are of the same nature with the dykes of the north

of Ireland.
2 G2

V. Some Remarks upon the Structure of Barbadoes, as connected
with Specimens of its Rocks.

By Josepu Sxey, M.D. Physician to the Forces.

Read June 19th, 1812.

Ir is not my intention to offer to the Society a mineralogical
description of those West Indian islands from which I have
brought specimens ; for, independently of the peculiar difficulties
attending close and accurate researches of this nature in such a
climate, my knowledge of the subject is too limited, and I am too
little conversant with such descriptions to venture upon any but
what the specimens themselves would seem to call for, in order
to explain the circumstances under which they were collected. As
however my friend Mr. Aikin has requested me to copy the few
and imperfect notes which I have taken upon the subject, I beg
leave to present them to the Society, together with the specimens,
trusting that they will be considered as little else than their accom-
panying catalogue.

I would beg permission to state that Barbadoes, which furnished
the specimens under notice, is an island totally unlike those im-
mediately near it, both in appearance and in structure, as will be
evident, when I lay before the Society specimens of the rocks of
St. Vincent and St. Lucie in my possession.

Dr. Sxey on the Geology of Barbadoes. 237

The land is seen to rise in a gentle swell from the coast towards
the middle of the island, excepting in a small district hereafter to
be noticed ; its highest hills have no great elevation, probably not
exceeding eight or nine hundred feet, and their general direction is
i think nearly north-west and south-east: its shores have no bold
promontories nor rocky headlands, excepting in some few spots
upon the windward, or north-eastern coast, which indeed is of a
bolder character, as is the case with all the islands in these seas
of which I have knowledge ; perhaps too the shore is more abrupt
at the opposite extremity of the island, the line of hills, which may
be said in a general way to pass through the middle of the island,
terminating here also in rocks of moderate height.

I understand that Barbadoes is similar in appearance and in
structure to a few of the other islands in this Archipelago ; to wit,
that half of Guadaloupe which is called Grande-Terre, and which
indeed forms a separate island from Basse-Terre, the two divisions
having a channel, occasionally, if not always, filled. Marigalante,
Antigua, and Santa Cruz also have a common structure with Bar-
badoes ; they all agree in being of moderate elevation, have no vol-
canic traces, and are all formed of limestone rock ; of this however
I have no personal knowledge. Barbadoes is in great part composed
of fossil madrepores, and traces of organic structure are to be met
with in almost every part of the island. These remains are par-
ticularly discoverable along the whole of the south and south-west
or leeward coast, and here I think the rocks assume a form which,
although it obtains more or less in every part of the island, is here
most discernible. The land, which when seen from the sea ap-
pears to rise uniformly from the coast, is observed on a nearer view
to consist of sucessive terraces rising in two or three gradations one
above the other; each terrace forming a plain of a quarter or half a

238 Dr. Sky on the Geology of Barbadoes.

mile in breadth, and terminated by a cliff of coral rock, varying in
elevation from twelve to more than twenty feet; sometimes indeed
having a considerably greater height. Although these terraces are
in general bounded by cliffs which run parallel to the line of the
coast, yet they are not wholly uninterrupted, for here and there
the high grounds advance towards the shore, and break their
continuity for a short space, where the terraced form of the land
is again taken up. :

The rocky boundaries to each terrace are formed by broken
pieces of madrepores of different species thrown about in great
confusion, held together by a calcareous cement of greater or less
hardness. Such are the madrepore with contiguous round cells,
No. 1. and the meandritical madrepore bored by mytuli, No. 2.

Near the garrison of St. Ann’s, and to the eastward of it, the
rocks bear the character of a dull compact chalky-looking limestone,
with ramose Alcyonia, No. 3, while considerably to the westward,
as in the parish of St. Peter’s, the rock is more distinctly coralloidal :
it contains also some natural caverns, from which very perfect
organic remains may de procured.

In sinking a well at the Naval Hospital, a little to the north-
east of St. Ann’s, the following specimens were met with in the
order in which they are enumerated, exhibiting in a striking —
manner the increasing compactness of the rock, in proportion to
the pressure of the incumbent mass.

1. A madrepore with contiguous round cells.

2. A madrepore with detached round cells.

3. A hard porous mass with terebratulites and lenticular con-
cretions, which are perhaps organic remains. _

4. A limestone analogous to the preceding but much harder.

in no part of this district, including almost all the leeward or

Dr. Sxey on the Geology of Barbadoes. 239

south and south-west side of the island, did I ever detect any other
rock than limestone, excepting that at very low water a bed of
calcareous sandstone is to be seen. ‘This rock is observed to dip
to the south-west at an angle of about 25° or 30°. There is no
coral rock incumbent upon it, but a small section of the broken
strata is here and there observable. Such appearances are to be
met with about a mile to the east of St. Ann’s, and again to the
westward of Bridgtown, near to Black Rock.

Towards the interior of the island this terraced appearance
becomes less observable, and here too the limestone rock loses
somewhat of its traces of organic structure, and occasionally even
passes into a calcareous tufa.

In the windward parish of St. Philip, where also there is less
of this terraced appearance, and where, if I mistake not, the hills
commence which form the middle or main ridge, the rock as-
sumes the external appearance of hard chalk; it is used for build-
ing, but effloresces on exposure to the atmosphere.

The island is almost destitute of running streams, excepting ina
district which I shall hereafter notice. Upon the leeward coast I
do not know of any constant stream; this no doubt is partly
owing to the porous nature of the rocks, and partly to the nu-
merous caves which are every where to be met with. These caves
are sometimes of large dimensions, and in the parish of St.
Thomas is one (usually shewn to strangers) which forms the bed of
a subterranean stream, the source and termination of which are
wholly unknown. As in all caves of this description, large stalac-

titic masses of fantastic forms depend from the roof.
I ought to notice another peculiarity in the features of this

island which is particularly observable among the hills which slope
from the central parts towards the leeward coast. The country is

240 Dr. Sky on the Geology of Barbadoes.

here intersected by deep fissures, called gullies, which have rent
asunder the cliffs, and are continued across the terraces in irregular
lines.

These rents in the rocks are sometimes of great depth but of
little breadth, and, generally speaking, are very precipitous in their

| sides, so as to be quite impassable, excepting here and there. Their
perpendicular sides exhibit the structure of the coralloidal rocks to
a considerable depth. Their bottoms are the beds of rapid torrents
in the rainy season, and almost the only places where any native
wood is now to be met with.

This scantiness of wood, together with the little elevation of the
island in any part, renders Barbadoes very liable to drought, much
more so than any of its neighbouring islands, and the inhabi-
tants already speculate upon the necessity of replanting with a view
to increase the fall of rain; but they will not find it an easy matter
to effect a growth of wood upon their arid rocks. Even in the island
of St. Vincent, where the quantity of rain is so much greater, failure
perpetually follows the attempt; probably because we are ignorant
of the successive means that have been required to produce the
luxuriant vegetation which, under natural operations, springs from
rocks almost bare of mould; and because too, we attempt to pro-
duce in a few years effects which have required ages to accomplish.

Upon the northern and north-eastern side of the island is a
district several miles in length, varying in breadth from half a mile
to two or three miles, which differs wholly from the rest of the
island in its general features. It is in fact a mountainous country
in miniature, and indeed that part of it which has most of this
character is called Scotland.

I never had an opportunity of exploring it minutely, but, as far

as I could judge, the recks are almost wholly calcareous, though

a“

Dr. Skpy on the Geology of Barbadbes. 241

less marked by organic remains than in the other districts. Sp.
No. 15, which, from its texture and the pearly lustre of its recent
fracture appears to be composed of shells and other organic remains
extremely comminuted, is from St. Joseph’s parish, which, al-
though not strictly a part of Scotland, has features in common
with it. Imbedded in this rock I found coarse flint, and a fine
grained ferruginous sandstone is in contact with it: this latter is
in nearly vertical strata, and is the only specimen of siliceous sand-
stone which I have met with in the island. The rocks near the
spot are frequently found impregnated with bitumen.

The following peculiarities are observable in the district; the
country is much more broken into hill and valley than any other

part of the island, it has few or no gullies, is watered by some
scanty streams, and has no traces of those successive stages which
give so peculiar a character to the opposite side of the island. Its
land boundary is in some places a very lofty cliff, and in every
part a ridge of pretty considerable elevation, having a precipitous
descent towards the north.

In the parish of St. Andrew this descent is the site of a spring
upon whose surface floats the bitumen which is to be met with
more or less in every part of the district, and is seen to exude
through the soil: near some small hollows which have been made to
collect this substance is a spring through whose muddy bottom
carbonated hydrogen bubbles and burns with a lambent flame
when a lighted taper is held above it.

The soil here appeared to be more argillaceous than that of the
rest of the island, and indeed there is a pottery of coarse ware in
Scotland, which I believe is the only part which furnishes the

material for it.*
* The nature of the soil in this district affects its productions, which are more those
of the mountainous islands than is the case generally in Barbadoes: the plantain flourishes

here and here only,
VOL. TI. 24

242 Dr. SKEY on the Geology of Barbadces.

Additional Note by Mr, Parkinson.

The specimens Nos. 1. and 4. illustrate the nature of some fossil
corals, showing that the forms in which they at present exist are
not those which belonged to the same substances in their original
state, and consequently ought not to affect their specific or generic
distinctions.

In some of these specimens only circular or polygonal cavities
occur, which possess no internal radiated structure, but have their
insides more or less crenulated. Dr. Skey’s specimen No. 4, is
chiefly composed of empty cylindrical cavities with slightly crenu-
lated sides; but in two of these cavities, near the center of the
specimen, erect lamellz are disposed in a stellular form, evincing
that the corresponding lamelle of the other cavities have been
removed by accident.

In other specimens are erect radiating lamelle not surrounded
by any parietes. Dr. Skey’s specimen No. 1. is also thus composed
of lamellz forming stellular columns, between which no parietes
are disposed. But in one.part of this specimen the compleat form
of the madrepore appears, two or three of the radiated cojumns
being here surrounded by similar parietes with those which are
seen without any columnar portion in specimen No. 4, showing
that this was the original form of the madrepore, and proving the
identity of the madreporean remains in both Dr. Skey’s specimens,
Nos. 1. and 4.

VI. Outlines of the Geology of Cambridgeshire.

By the Rev. J. Hartsrone, F.R. & L.S. Woodwardian Professor in
the University of Cambridge.

Read November 18th, 1814.

Var upland parts of Cambridgeshire consist of chalk hills,
being part of that great range which traverses the island in a south-
easterly direction, from Dorsetshire to the Yorkshire coast. At
their northern extremity they appear to rest upon an extensive
bed of blue clay, provincially called gault. They are composed
of both the varieties of chalk; of the upper containing the com-
mon black flint in abundance ; and the lower or grey chalk, which
contains little or none. If a line be drawn from Royston by
Balsham to Newmarket, it will pretty exactly define the limits of
both the varieties ; the hills to the eastward being composed of the
upper beds, while those to the west consist of the lower or grey
chalk. Further to the east, on the borders of Suffolk and also of
Essex, the chalk disappears under a thick bed of clay, which
occasions a corresponding difference in the soil and its produce.
To the west, a succession of hills composed of beds of grey chalk
with wide intervening vallies of gault occur; till on the extremity
of the county, at Gamlingay and Potton, a tract of sand comes in,
evidently connecting the strata of Cambridgeshire with those of
Bedfordshire. And here the features of the former county undergo
2H 2

944 PROFESSOR HAILSTONE on the

a manifest alteration, its high elevations subsiding by degrees into
the sand hills of the latter.

Upon some of the highest hills near Cambridge, a deposit of
gravel and loose stones in horizontal layers, has lately been found,
resting immediately upon the chalk. This gravel differs in so
many respects from the red ferruginous gravel found dispersed in
patches over the gault in the subjacent flat, that I think it must be
considered as a deposit of a different epoch. It contains numerous
fragments of strata belonging to the oolite series, which occur in
the neighbouring counties of Northampton and Rutland, surround-
ing Cambridge on the west and north-west. Pieces of basaltic
rocks are sometimes found, but these are not very common. These
fragments are of all sizes, and worn down in different degrees.
Some are pebbles intirely rounded ; others have their edges merely
blunted. Some appear so tender and so little capable of resistance,
that it is difficult to conceive how they have been transported
without being entirely destroyed. The prevailing material of these
masses of gravel, is the pale blue or light grey variety of flint,
with numerous traces of the alcyonium or other similar bodies in
its substance.

According to my observation, this variety of chalk flint is not so
‘common in the southern parts of this great chain, whilst in its
continuation through Lincolnshire and Yorkshire, scarce any other
is to be met with. The two principal deposits of the gravel of
which I have been speaking are to be seen on the summit. of
Gogmagog hills, and on Harston hill about five miles to the south
of the former. The height of these hills may be estimated, at 800
feet above the river at Cambridge.

Harston hill has been examined by Mr. Warburton, Secretary of
the Geological Society, who has obligingly communicated the

Geology of Cambridgeshire. 245

result of his observations to me. Mine were principally made at
the pit on Gogmagog hills; and as the contents of the two pits
seem to differ in some respects, I have great pleasure in subjoining
his remarks in the same terms as they were conveyed to me. His
conjectures as to the cause of these alluvial deposits, will be read
with great interest by Geologists.

“¢ The hill at Harston is of a conical form, and situated about a
quarter of a mile S. E. of the village, and about five miles S. W. of
Cambridge. I selected from the rubble which is deposited on the
summit of the hill the following specimens.

1. Rounded pebbles of very hard chalk, scarcely softer than the
Antrim limestone. These compose three-fourths of the mass
of the rubble.

2, Angular masses of striped flint. These are numerous and very
large; one cylindrical piece that 1 measured: being one-third
of a foot in diameter and one foot long.

3. Fragments of septaria.

4, Fragments of a shelly limestone.

5. Ochreous balls, resulting probably from the decomposition of
pyritous nodules.

6. Angular or scarcely rounded pebbles of trap or greenstone.

7. Organic remains, viz.

a small fusiform belemnite ;

a large belemnite ;

a small gryphite ;

a large oyster; vide fig. 7& 8. Pl. 8. Townshend;
some bones and teeth.

246 PROFESSOR HAILSTONE on the

The appearance of these specimens is not very inviting; but
they are not without interest.

The pebbles of hard chalk are probably the remnants of the bed
which immediately covers the green sand and the gault, of which
these are either fragments rounded by attrition, or they are the
nodules peculiar to the lower chalk, (as may be seen in Wiltshire,)
washed out of the bed itself, which is disintegrated.

No. 2 is probably a variety of common flint; specimens of this
substance are not uncommon, in which there is an appearance, as
in a Scotch pebble, of alternate layers of deposition. The action
of air and moisture might render these natural divisions more
visible, just as slates are obtained by the exposure of the blocks of
fissile stone to the weather.

As other beds, besides the London clay, contain septaria, we
cannot say from what bed the fragments of this substance are
derived ; nor will any of the specimens previous to No. 6, furnish
any data for guessing the nature and direction of the current,
which has heaped together this mass of confusion.

The mass of greenstone nearest to Cambridge is found in the
toadstone beds of Derbyshire, to some specimens of which the
pebble No. 6, bears a close resemblance. Few of these pebbles.
weigh less than 8 ounces.

The large oyster is the same with fig. 7 and 8 of Pl. 8 of
Townshend’s work, and belongs to the bed which underlies the
coral rag. |

The large belemnite is peculiar, I believe, to the lower oolite.

The bassetings of the three last mentioned beds, that is, of the
toadstone, the coral rag and the lower oolite, are found (at least in
England) only in a direction west of Cambridge ; so that we are
led to explain the accumulation of these alluvia by the agency of a
powerful current flowing from west to east.

Geology of Cambridgeshire. ‘247

The rubble rests on the summit of a conical hillock, the sides of
which constst of naked grey chalk; than which one can hardly
suppose a situation more unfavourable for the accumulation of
alluvial matter; at any rate why is not this found in as great
abundance on the flanks as on the summit of the hillock ? This
looks like the partial destruction of an alluvial level by some sub-
sequent cause, the discovery of which I leave to more learned
members of the Society.”

Thus far Mr. Warburton. With respect to the hard chalk peb-
bles it may be proper to remark, that in some parts of the chalk
formation a harder bed is found, of a close grain and compact
texture, which might very well supply the material from which
these pebbles have been formed. This bed may be seen at Sudbury
in Suffolk, and I have also observed it in some parts of the York-
shire wolds. The striped variety of flint is also to be met with in
the ordinary chalk of the same hills. I have before observed that
a distinction must be made betwixt this deposit and the ordinary
gravel found at a lower level; and in fact throughout the Isle of
Ely such a distinction is universally admitted, the one being called
the white gravel and the other the red. The same distinction is
known in Dorsetshire, as I learn from De Luc’s Travels, vol. ii.
p- 77, in a passage particularly illustrative of these two deposits.

It would be unnecessary to trouble the Society with any obser-
vations on the chalk bed with flints, as I am not aware that they
present any thing new, and their phenomena may be studied in
other parts of the island to greater advantage. I pass therefore to
the lower beds or grey chalk, which composes by far the greatest
part of the hills of Cambridgeshire. These beds, as is well known,
contain no flints, but, not uncommonly, dispersed masses of the

248 ProressOR HAILSTONE on the

radiated pyrites, globular or kidney-form. It is considerably
harder than the common chalk and its colour is usually some shade
of grey. It is well known in this county under the name of clunch,
and is the material from which the best lime is burnt. Some of
the beds are hard enough to serve the purpose of building stone,
and are quarried and shaped in blocks for that purpose. It also
endures the fire well, and, like the Ryegate stone in London, is
much esteemed for the backs of grates and other similar appli-
cations.

This stone is dug in the greatest quantities at Reach, a small
hamlet in the parish of Burwell, situated on the skirts of the fen
country precisely where the Devil’s ditch terminates in that di-
rection. The excavations at this place are immense.

Clunch, when burnt, affords a lime in such universal esteem
that the crude material is sent from hence for that purpose as far as
Peterborough and other distant places, within reach of the water
carriage of that level district. .

The bedding of a chalk hill is difficult to ascertain, on account
of the great number and irregularity of the rifts and joints inter-
secting the stone in all directions. By careful observations however,
made in different places, 1 am enabled to state that the general
direction of the beds is from the N. E. to the S. W. and that they —
have a gentle inclination to the S. E, Their direction consequently
coincides with the line that I have mentioned above, as dividing
the upper from the lower chalk.

In one of the pits at Reach a bed of clunch occurs, which differs
from the ordinary sort and presents some remarkable appearances ;
the mass itself is much harder, and stuck full of concretions of a
yellow indurated marl: outwardly they are of a green colour
arising from the oxide of iron: they are in general kidney-shaped

Geology of Cambridgeshire. 249

and of all: sizes, from a hazel nut to an ordinary potatoe. The
shape of the bed also deserves notice ; its general thickness is about
fifteen inches, which it preserves for near thirty yards, as appears
in the section of the quarry; it then diminishes at each end to a
thin edge, and at length totally disappears. At a short distance in
front, there happens to be left by the quarry-men an _ insulated
butt, where this bed is not found at the level where it might be
expected ; the conclusion therefore is, that it has terminated also in
this direction in a similar manner: thus, as to its figure, putting
the practical geologist in mind of the mineral deposit called a pipe-
work in the lead countries. I must however observe that in an
extensive pit at Kneesworth on the other side of the county, the
same bed occurs again, where it preserves an uniform thickness and
direction like the other beds with which it is associated. In
general, I take this to be the bed which Mr. Townsend* notices as
hard and rubbly, and found in descending the hills from Everly to
the vale of Pewsey. It has also been observed by Mr. Warburton
at Marlborough.

I have never been able to observe any strong_line of separation
betwixt the clunch and the succeeding stratum of gault on which -
it rests. I believe they pass by degrees into each other. The
lower beds of clunch become more sandy, and gradually assume
the nature of an argillaceous loam. In the next observable stage
of transition, the mass assumes a greenish grey colour, and a
plentiful admixture of dark green sand is uniformly dispersed
through its substance. At the same time it contains numerous
irregular dark brown nodules of a ferruginous indurated marl.
At length these foreign matters disappear, the mass becomes
uniform and ends in the bluish clay or argillaceous marle called

‘ * A Character of Moses, vol. 1, page 98.
VOL. 111. 21

250 ProressoR HAILsTONE on the Geology of Cambridgeshire.

gault. This occurrence of green sand in the confines of the two
beds wag first noticed by Mr. Warburton at the brick pits near the
Castle hill, from which he inferred that it always takes place under
the same circumstances: an inference which is borne out by the
testimony of the most experienced brickmakers about Cambridge.

I am at a loss where to class the bed of sand and sandstone
which lies over the gault.at Ely, and forms in some measure the
elevation on which that city stands. It contains particles of green
sand, but not in sufficient quantity to be characteristic. It is
principally a concrete of siliceous sand, with small rounded frag-
ments of ironstone and quartz pebbles: the bed is from eight to
twelve feet in thickness, and perhaps an alluvial deposit.

It is unnecessary to trouble the Society with an enumeration of
all the organic remains that are to be found in the clunch or chalk
beds, they are in general the same as occur in other parts of the
kingdom where the chalk formation presents itself. Of the
remains -of fish we find their teeth, bony palates, and in many
‘cases their brown scales not much altered. Cornua ammonis occur
and some bivalves apparently of the chama and mytilus genera.
Of the former genus I have found the haliotidea very distinct.
The anomia terebratula occurs in the beds at Reach. In the
vegetable kingdom the -fruit cones of Cherry Hinton deserve a
particular notice. As early as Woodward’s time this fossil had
attracted the attention of ‘naturalists, and two very perfect speci-
mens in his collection appear to put.their vegetable origin beyond
‘doubt. In confirmation of this opinion, I beg to refer to a fossil
in the collection which I have the honor to transmit, which I met
with at the same pit, and seems to be the impression of a branch
of some vegetable of the fir tribe, with the linear leaves surround-
ing it.

4

VIL. Some Observations on a Bed of Trap occurring in the Colliery of
Birch Fill, near Walsall, in Staffordshire.

By Artuur Arkin, Esq. Secretary to the Geological Society.

Read November 20th, 1812.

Aurnoucu several instances have come under my personal
notice in Shropshire and the adjacent counties, of the occurrence of
trap rock in connection with the coal-formation, yet in all these
cases the trap either forms the basis on which the coal strata rest, or
is incumbent on them; or, in the form of dykes, fills up the frac-
tures or faults. Being informed however by Mr. James (one of
the members of our Society) that a bed of trap had been pierced
through in several places in a colliery, at Birch-hill near Walsall in
Staffordshire, which has lately come into his possession, I took an
opportunity of visiting the spot in the course of the fast summer,
and beg leave to lay before the Society the result of my examination,

On my arrival I found that the lower part of the works (in
which the bed of trap is situated) was not as yet sufficiently freed
from water to admit of actual inspection ; but being furnished with

212

252 Mr. AIKIn on a Bed of Trap

a plan of the colliery and with registers of the strata pierced through
in sinking the three deepest pits, having also an opportunity of
questioning several intelligent miners who had themselves worked
in the colliery, and of examining many tons of trap rock and of
the adjacent beds which had been brought to the surface, I think
that there will be found no material error in the following state-
ment.

The surface of the colliery at Birch-hill (Pl. 12. fig. 1.) somewhat
exceeds 83 acres; and is itself only part of a more extensive coal-
field, the portions of which adjacent to the present colliery have
been worked out so long ago as to preclude the obtaining
any correct information concerning them. The ground rises with
a very gentle slope on the east, falling nearly flat and becoming
marshy on the west. On the south-western edge of the colliery is
a low ridge, from 20 to 30 feet above the level of the marshy
land at its foot, from 70 to 100 yards broad, and extending along
the southern edge of the colliery for 3 or 4 hundred yards, till by
degrees it coalesces with the general slope of the land, and is no
longer distinguishable. This ridge is named the green rock fault,
and forms the separation between the Birch hill colliery and an
exhausted one adjacent to it on the south.

There have been about twenty pits sunk at different times, more
than half of which are in the south-western angle of the colliery ;
not one of these has reached the bottom of the coal-formation, and
therefore the rock upon which it rests is unknown: I apprehend

however (from the general analogy of this part of the country) that
the fundamental rock is floctz-limestone.

in Birch-hill Colliery. — 253

The following is a list of the strata in pit B, from the surface to
the greatest depth that has been hitherto attained, viz. 216 feet.

DOMME ERIC SOar ce tes semen ste Steet er erT ees 4; 0
Blue and grey clunch with balls and measures of ironstone | 12 | 6
Lol yal VE a Td Sy ee ae la aati eiarl a voty ts 2) 0
Clunch mixed with ironstone, and including a bed of the!

Meme: PS imehes CHICK ss oe oo a6 eg sore Meee nje e wlete at 35 | 6

The open-work, and the six pits called by the miners
Stone-pits (marked @,ain the plan) are for the purpose of
procuring the ironstone contained in the beds already
mentioned, and therefore on an average do not exceed the
depth of 54 feet.

Daal CUOl WOFKEMP cco. ratert cet can tere tere ee 0; 10
Hire;clayy \. «a hszst Spehis Se sracpdwokntpeds oped 2 Fhe: Pips as Eekyns 5) 0
Rock binds (slaty clayey sandstone) ..........-....00-: 27 | 2
Brst coaliorn Yard woallis. 5% fy ciel. Qe atiseelds Gate ole Wik 2| 2
89 2
The Yard coal is the first coal which has been worked : |
it is soft, and applicable only to domestic purposes or to
the roasting of the ironstone: its thickness varies from 26
inches to a yard. The three pits marked d in the plan ar
sunk into this bed: their average depth does not exceec
90 feet.
Sandstone, the upper part of the bed slaty, the lower compaci{ 38 | 4
Pinas ete gal C9. 12 AKITA eh LR ALE ae OR. Bibed
This is the second workable coal; it is of good quality
and is coaked for the use of the furnace.
Alternations of compact sandstone, slaty sandstone, slaty
CHAY y ANC Clay Wile ne atee eitte Oe ela Me onan s e edethe chalet 28 | 2
Coal and bituminous slate (not worked)....... Spe craece 1 6
EYIGUNAS ENA oats ee eur aie are ay ehF ¢ so siete Wialale tee chtte ee ae ec Ve eae
Sandstone and indurated clay......5.0..0s0 eee eveees 57) 6
Black slaty clay inclosing three beds of ironstone of 9, 3,
and S2:intehes im thickness 4... sy. + sraiajaieys «\enaeh elapebed. | 10; 10
Tra EID LOU) ale vicicicle aie 0 =e cimeratr ei ctolate «> aot a es myo
P(g ) soni
The pits A & C are sunk into the trap, the ene to the
depth of half a yard, the other to the depth of five yards,
but neither of them passes through this bed.
MdUrAated SAMUSLORE..... 2 ccs. wields cleo tie Sols celeste 0 wie es si 0
|Carbonaceous slaty clay and blind coal................. 4| 4
Sidty Glavemecerstea stays oe de cee «lerca\> ere ore alee etre mine eee ry 6
Strong yhamalbitiminoust¢oal |.) tysio.. ileteleitiisneep ckebieto tee ks 4) 46
_ The above two beds of coal, with the thin interposed
bed of slaty clay, form the third coal which is worked.
UMM CLAY. sits) «n'a 20sec n\n p <.0 hs neko eie.9 ais sale Wise ates olnials 2; 0

The Engine pit, the Bye pit, and the pit marked B,

terminate in this bed.

' 254 Mr. Arkin on a Bed of Trap

Besides the green-rock fault, already mentioned, there is another
which passes through the colliery longitudinally in a direction
E. by S. and W. by N._ This fault is a mere dislocation of the
strata causing a depression of 72 feet to the S.: a smaller fault or
Rider branches off nearly due W. from the larger one causing a
further depression of 4 feet in the strata which lie immediately to
the S. of it. The junction of these two faults takes place precisely
under the Furnace, 7 ,

The beds on each side of the central fault rise nearly S. at an
angle of about 6°; but, in the immediate vicinity of the green-rock
fault, the second coal and all the beds lying above it (as far as they
have been explored) are thrown up at an angle so rapidly increas-
ing as, in the space of about 100 yards, tc amount to 25°.

None of the beds are known to vary materially in thickness
except the trap. The thickness of this latter in the Engine pit and
in the Bye pit amounts to 24 feet, but in the pit B it is diminished
to 12 feet, and in the pit D which is sunk down to the third coal
the trap is wholly wanting. The miners themselves conclude
from these facts, and apparently with reason, that the bed of trap
is merely a great wedge from the green-rock fault which has
intruded itself between the proper coal strata, but is by no means
co-extensive with them.

To the geologist the circumstances connected with the relative
situation of the trap and with the state of the beds that lie imme-
diately above and below it are of singular interest; and it happens
fortunately that the two most interesting of these beds, namely the
indurated sandstone and the blind coal, have been explored to the
distance of several yards. This was effected in driving a heading
for ventilation from pit A to the pit B, see section Pl. 12, fig. 2.:
this heading was begun in the first or yard coal, but on passing the

in Birch-bill Colliery. 955

great fault (which was then first discovered) the miners found
themselves unexpectedly in the upper bed of the third coal (i.e. the
blind coal), and in this they continued to drive forwards the
heading to pit B, a distance of about 100 yards.

I now ‘proceed to a more particular description of the trap and
‘of the adjacent beds.

The colour of the trap is a dark bluish green; it has a glimmer-

ing lustre from the intermixture of minute, shining, crystalline
Jaminz ; its fracture is uneven, and it breaks into irregular wedge-
shaped blunt edged fragments; it is tough, acquiring a kind of
polish under the hammer, moderately hard and rather heavy. It
attracts very strongly the magnetic needle, but does not exhibit
any signs of polarity: it effervesces moderately on being immersed
in cold dilute muriatic acid, and on examination with a Jens
appears to consist of felspar, of calcareous spar, of minute shining
black grains, and of a brownish, blackish, and bluish green
substance, which I suppose would generally be considered as amor-
‘phous hornblende: it is to be remarked however of this latter sub-
Stance that it exhibits no appearance of crystalline laminz, and that
if a piece of the entire rock be digested in boiling dilute nitro-
muriatic -acid this green matter is almost entirely dissolved with
-considerable effervescence ; and the stone assumes a greyish white
colour consisting almost wholly of crystalline lamin of felspar.

This trap or greenstone is penetrated by contemporaneous
nearly «vertical veins of calcareous spar, fromthe size of a mere
thread to about half an inch in thickness. The rock, although very
compact in its recent state, after a few weeks exposure to the.air, _
acquires a liver-brown-colour and crumbles to pieces. F

The slaty clay, with subordinate beds-of ironstone, which lieg
above the greenstone, differs but little from the common slaty clay

256 Mr. A1k1n on a Bed of Trap

of the coal formation. This however is by no means the case
with the three beds that lie immediately below the greenstone,
namely, the indurated sandstone, the carbonaceous slaty clay, and
the blind coal.

The indurated sandstone is of a yellowish grey colour, dense, com-
pact and ponderous ; it consists essentially of fine grains of quartzy
sand and silvery mica, and contains very slender imperfect veins of
calcareous spar, and small irregular granular concretions of ferrife-
rous carbonate of lime : these concretions decompose by exposure to
the air, and give the external surface of the stone a brownish
yellow ochry tinge. In the specimens that have come under my
notice, the surface of the greenstone where it is in contact with
the sandstone, is of a brown colour, and decomposed to the
depth of an inch or more; but I have not observed any direct
mutual penetration of the two beds. The lower part of the sand-
stone, however, is considerably broken, and angular pieces of the
carbonaceous slaty clay (technically called daé#) occur, completely
involved in the sandstone,

The characters of the batt, if taken from that part of the bed
where it is not covered by the greenstone, are those of common
bituminous shale or soft slaty clay, inclosing seams of pitch coal —
about one-fifth of an inch in thickness: but wherever this bed is
covered by the greenstone, the slaty clay is considerably indurated,
the ccal is also harder and more compact, and possesses a brilliant
semi-metallic lustre ; and: both the clay and the coal are wholly
destitute of bitumen.

Below the batt lies a coal four feet thick, which, where covered
by the greenstone, has a shining somewhat iridescent lustre; it is
entirely destitute of bitumen, and when put in the fire burns
rapidly, like common cinder, differing materially in this respect

in Birch Fill Colliery. 25T

from the Culm of South Wales, or the blind coal of Kilkenny;
but where this coal is not covered by the greenstone, it exhibits
the usual characters of common bituminous stone coal.

The beds below this coal differ in no material respect from
similar beds in other collieries.

Hence it appears that the Birch-hill colliery presents the follow-
ing important facts: First, the existence of a bed of greenstone
interposed between the usual strata of the coal formation, but not
co-extensive with them; and secondly, that the coal and bitumi-
nous shale, where they are covered by the greenstone but protected
from actual contact with it by an indurated sandstone a yard in
thickness, differ materially in many respects, but chiefly in being
deprived of bitumen, from those parts of the same beds where
they are not covered by the greenstone. The works have not in-
deed been sufficiently opened to demonstrate that the changes just
mentioned are strictly co-extensive with the greenstone, yet I think
we may infer by fair analogy that such is the case; and that the
greenstone is necessarily concerned in bringing about these changes.

Professor Jameson, in his mineralogical account of Dumfries-
shire, mentions beds of greenstone occurring in the independent
coal formation ; and I at first took for granted, that the greenstone
above described was also a true bed. On further consideration,
however, I am rather inclined to adopt a contrary opinion, for the
following reasons : |

In the first place the green rock fault being composed of pre-
cisely the same kind of greenstone as the bed is, renders it probable
that the one is a continuation of the other; and this is still further
confirmed by the gradual thinning out of this bed as it recedes from
the fault; for in the pit B, the most distant one that has been as
yet sunk through the greenstone, this bed is 12 feet thick, while in

VOL. III. 2K

258 Mr. A1kIN on a Bed of Trap, &c.

the engine and bye pits, which are the nearest to the fault, the
same bed is 27 feet thick. The actual junction of the greenstone
of the bed with that of the fault has not. indeed been proved, but
from the very little unexplored spaeq at present between them,
there can exist but littke doubt I imagine as to the fact. Now,
though it is possible that the outburst of the greenstone (supposing
it to be really a bed) may so coincide with the elevation and cur-
vature of the ridge as, with a thickness of no more than about.30
feet, to give the appearance of a rock 60 or 100 yards across, yet
this hypothesis is scarcely consistent with the rapid increase of the
angle at which the strata above the greenstone bed are elevated in
the vicinity of the green rock fault, advancing in a few yards from
6° to 25°. The absence of the greenstone bed in the pit D.
though it is full as near the line of bearing of the fault as the
engine and bye pits are, is a further support of the opinion that I
have hazarded.. Upon the whole, then, I am inclined to consider
the green rock fault as a fissure in the coal field, filled up by green-
stone, and the supposed greenstone bed as a wedge-shaped pros
longation of the same.

With regard to the mode in which this and similar fissures have been .
filled, whether by deposition of the constituents of greenstone from
solution or suspension in a superincumbent aqueous fluid, or by the
bursting from below upwards of earthy matter, either melted or in
the state of boiling hot mud, like the mud-volcanoes of Mexico
and of the island of Taman in the sea of Asof, I shall not pretend
to decide. 3

-VITL. = Geological Description of Glen Tilt.

By Joun Mac Cuttocn, M.D.F.L.S. President of the Geological Society,
Chemist to the Ordnance, and Lecturer on Chemistry at the Royal
Military Academy at Woolwich.

4

Read Dec. 3, 1813, and the Supplementary Additions Dee. 16, 1815.

L is well known that the appearance of the granite in various
parts of the valley of the Tilt afforded to Dr. Hutton one of the
original arguments on which his theory was founded. Hence
this spot has acquired among geologists a sort of classical celebrity,
sufficient to render it an object of interest, independently of that
which is excited by the intricate and remarkable disposition ' of its
rocks. Observations, now more numerous than in his day, have
brought to light so many facts similar to those which appeared to.
him so important, that there is no difficulty in pointing out abun-
dant instances of an occurrence once supposed rare. But having
had occasion while examining these rocks to observe other interest-
ing appearances, which have been either misapprehended or over-
looked, I consider that a notice of them will not be unacceptable
to the Society. The notice is accompanied by such specimens and
drawings as are requisite for the illustration of the subject.

In describing Glen ‘Tilt I have been under the necessity of differ-
ing on certain points from those who have preceded me. An ex-
amination of many of these points of difference would lead to
discussions as endless as they would be fruitless, and give this

2K 2

260 Dr. Mac Cuttocu on the Geology of Glen Tilt.

paper the aspect of a controversial essay, rather than of that to
which it alone pretends, a descriptive one; for which reason I
have chosen to describe it precisely as it appeared to me. Where
my description differs from that of others, the differences will be
found to consist at times in a difference of opinion respecting
the denominations of rocks, while on other occasions they are
much too great to admit of their arising froma different use of
the same terms, or a different mode of contemplating the same
phenomena; they are differences respecting facts, and are there-
fore the less fit subjects of discussion.

As the local circumstances which require to be examined before
an adequate notion can be formed of the true structure of this in-
teresting place occupy a considerable range of country, and as.
inevitable confusion would follow any attempt to describe the mi-
neral beds and their geological connections in their natural order,
on account of their perpetual interference with the geographical
disposition of the ground, I have chosen to adopt a geographical
method. In so doing I shall the more readily be understood as far
as the simple specification of facts goes, and those who shall
‘incline to follow me in the investigation of this spot will also be.
furnished with a clue by which they may trace the description, and
the more easily confirm or refute, as it may happen, that which I
shall relate. In the present state of geological knowledge, this
method of proceeding seems absolutely: necessary. Like the detail
of chemical experiments it enables the reader to follow step by
step the appearances from which the general results have been de-
duced, to examine the inferences as they are drawn from the phe-
nomena, and finally to determine on the legitimacy of the con-
clusion. Such inferences or such general conclusions, as appear

to me to result from a comparison of these facts duly approximated,
-will be stated afterwards.

Dr. Mac Currocn on the Geology of Glen Tilt. 261

In examining such a valley as that which is the subject of
the present paper, the course of the river, as well as the
ranges of hills which bound it, must necessarily enter into the
history of its geological formation. Where these are of similar
structure it is easy to comprehend the whole in one line of descrip-
tion, taking the course of the river for a guide. But in Glen
Tilt a dissimilarity so complete is observed between the opposite
sides of the valley, and the numerous and interesting phenomena
which occur in the bed of the stream itself are so dissimilar to
both, that it is impossible to convey an adequate idea of the whole
structure without a distinct examination of the three several lines.
A perpetual transference of the imaginary spectator from ‘one point
to another, would produce as much confusion in the narration, as
such a proceeding in examining the ground would obscure the
judgment and puzzle the investigation of the real observer. I have
therefore chosen to detail the examination of the three lines se-
parately, and have commenced with the river as the most natural
if not the most useful method, describing in succession the ranges
of hills, of which the history is required to render the phenomena
which are to be seen in the river intelligible.

The Tilt has its rise in a small loch not far from that long valley
which is the common division of the waters running east and west
to join the Dee on one hand and the Tumel on the other. As it
enters that valley it falls immediately into a line tending westward,
from which it deviates towards the south-west before its termination
in the Garry, the narrow bottom of the glen affording but little
room for lateral deviations, and its direction being subject to no
material variation, For two or three miles its course lies so much
through alluvial matter that it offers nothing to the spectator; nog
does any material feature occur before its junction with: the Tarff.

262 Dr. Mac Cutrocu on the Geology of Glen Tilt.

Occasionally it may be seen cutting its way through quartz rock,
through schist, and, not. long before its arrival at the Tarff,
through beds of dark bluish limestone. One solitary portion of
pure white limestone or marble is also visible in this part of its
course. Where it joins the Tarff it also receives another stream of
considerable magnitude, flowing from Glen More and collecting the
waters from a set of vallies that lie between the foot of Carn-ree
and the head of Glen Fernat, as well as from those corys of Ben
Gloe which tend in this direction.

It will be unnecessary to particularize the several streams which it
receives during its course to the Garry, unless where their sections
offer material information respecting the structure of the neighbour-
ing hills.

Having passed the Tarff it begins to run in amore rocky channel,
and though often, and for considerable spaces, its true bed is con-
cealed by the alluvial matter which it has accumulated, enough
remains exposed to excite the curiosity, and employ no small
portion of the time of a geologist. Although in enumerating and
describing these several points where the natural bed is visible,
I have used all my endeavours to specify the particular places
where they occur, yet in this respect the description will still be
deficient. Even if an accurate survey of the ground were made,
the want of points of reference in a valley which possesses so few
permanent marks for distances, would. prevent me from referring to
them as accurately as would be desired by those who might wish to
follow the same track. The difficult nature of the banks, and the
many inaccessible points which the river possesses, combined with
t!.e dangerous violence of its waters, frequently also deny access,
and may consequently have led to omissions. Such omissicns will
also be found to arise from another cause, to which may equally be

Dr. Mac Cuttocnu on the Geology of Glen Tilt. 263

referred some discrepancies and errors in the measurements of the
remarkable rocks which are seen in its bed. This cause is the variable
state of the water, which at times exposing more or less of these
projections in its bottom, alters their apparent magnitude as well as
their number. I have been rendered sensible of these differences
by examining its course at different periods, but since some con-
fusion would have resulted from any attempt to correct the first
examination which I made, I have preferred giving it as it was first
recorded, with the caution against implicit reliance in the mea-
surements which I have now laid down. It is only necessary
to say that the observations were made in a kind of medium height
of the water, and that as the geological consequences are in no
wise affected by this sort of inaccuracy, I held it unworthy of
correction. The statement of the circumstance was however
necessary, Jest the discovery of inaccuracies of this nature might
lead to doubts with regard to more important observations.
The measurement given in yards is merely a rude computation
from pacing, but it is fully adequate to the purposes in view; since
neither the facts nor reasonings can in any way be altered by a
greater or less nicety of admeasurement.

_ Descending therefore the course of the river from Poll Tarff, (See
Map plate 13) the junction of that stream with the Tilt, a large body
of granite will be seen crossing it above the Shepherd’s hut, and a
small granite vein may also be observed above it at a little distance.
The bed of the river from Poll Tarff to this point, wherever it is visi-
ble consists of dark blue limestone alternating with quartz rock.
At the distance of four or five hundred yards from the burn of
Aldianachie, a large rock consisting of a complicated mixture of
granite and schist crosses the Tilt again. I shall not here dwell
upon the circumstances which attend this mixture, as better oppor=
tunities of describing them will occur hereafter.

264 Dr. Mac Cuttocu on the Geology of Glen Tilt.

It is not far below this place, but at a distance which I have
neglected to note, that a great portion of a limestone bed will be
found crossing the river. It is much centorted, and is also reticu-
lated with a few granite veins. Here the alternation of the lime-
stone with the quartz rock is also visible, and they cross the river
together. The limestone is in this place uncommonly hard, and
in its composition very siliceous. Its external aspect where it
is worn by the action of the water, is not much unlike that of a
granite or porphyry, and it has in fact been sometimes mistaken
for one or other of these rocks. Continuing to descend nothing
remarkable occurs till we arrive within about two miles of Forest
lodge, where a rock like those last mentioned, traverses
the bed of the river. This rock consists of a great mass of
red granite so mixed with quartz rock and hornblende schist, that
neither pen nor pencil can describe their confusion. Limestone
may be observed both at its upper and lower edge, and this is
traversed and reticulated by small granite veins. The whole mass
occupies a space of about 150 yards. It is proper to remark here,
that the blanks which occur in this account of the bed of the river
are such as in general arise from its course being over a bed of
alluvial matter which covers and conceals the fundamental rock,
while in other cases they arise from those portions of the natural
bed which are visible being trivial or unimportant, or from the state’
of the water which prevented its bottom from being seen.

The next, and’ of all perhaps the most remarkable rock to be
observed in the course of the Tilt, occurs at a bridge’a short distance
above Forest lodge. A large mass of red granite is first seen occu-
pying the bed of the river for a considerable space both above and
below that bridge. Associated with this mass of granite are various’
rocks, so disposed and intermingled that neither description, nor draw-

Dr. Mac Cuttocu on the Geology of Glen Tilt. 265

ing, nor specimens, can give an adequate idea of their disposition
and confusion. The drawings which accompany this paper
may serve to illustrate a description which can only be general,
since no drawing less in size than the rock itself could give an
accurate representation of the place.* In, contact with this great
- mass of granite, which for a certain space offers no very particular
feature, are seen rocks of a schistose nature. These are succeeded
by blue limestone, and subsequently by schist and granite, but in
a state of disorder so inexplicable, that I do not attempt to describe
their relative positions. No appearance of parallelism is to be seen
in the schistose rock, but the limestone, although much bent and
twisted, has the aspect either of a complicated vein, or of the edges
of a bed in a vertical position, the portions of which have been
split asunder and filled with other materials. The lamellar form of
this limestone and its connections with the surrounding rocks,
leave however: no doubt of its being the exposed edge of a bed,
and it must at the same time be remarked that besides being placed
in a vertical position, the line of its course is at right angles or
nearly so to the general bearing of the strata, of which it seems
once to have formed a regular constituent part. Viewing the
whole of this compound mass of schist and limestone as a single
rock, and the granite as another, it is easily seen on the most su-
perficial glance, from the strong contrast between the dark grey
of the former and the red of the latter, that the dark rock is
intersected and disturbed by innumerable veins of granite.
These traverse it in every possible direction, and are of various
sizes, the smallest not exceeding that of a thread, and
reticulating the dark rock in a most intricate and amusing

* Vide Plates 14, 15, 16, 17, 18.

VOL. III OV;

266 Dr. Mac Cuxrrocn on the Geology of Glen Tilt.

manner. Such is the ordinary view which has been taken by one
class of observers of this rock, as well as of all the other rocks seen
in Glen Tilt. They have been looked upon as mere masses of
schist intersected by veins of granite, the larger bodies of granite
being considered as veins, the origin and direction of which were un-
known, and the smaller ones as ramifications proceeding from them.
A different class of observers, seeing in this imagined schist
nothing but its approximate position with granite, have considered
it as offering an example of the alternation of these two rocks. In
whatever way the different theories may be affected by these dis-
tinct views of this case, I have no inclination at present to enquire.
If one of them be incorrect, the other is imperfect, and the object
of this paper is rather to give a more full account of the appear-
ances to be observed in this place, than to renew a controversy on
the same grounds on which it has already been agitated.

Independently of such considerations, the disposition of the
rocks at this place, as well as in other parts of the Tilt, are so
curious, and as yet so solitary and new, as to render them highly
attractive and well worthy of record. It will however be seen
hereafter, that the history of these several appearances, even if it
should not be supposed to add any strength to the general theory
respecting the posteriority of granite, serves at least to give us an
accurate idea of the real structure of the valley itself.

The remarkable novelty here visible, and in which the junction
of the granite with the superincumbent rocks differs from all similar
junctions formerly described, is that of the interference of granite
and limestone. The granite veins which traverse the schist, pass
equally into the limestone which accompanies it. These veins are oc-
«asionally of large size. In this case they can sometimes be traced inte

Dr. Mac Cuttocn on the Geology of Glen Tilt. 267

the larger masses of granite with the same ease as when they traverse
the schist : in others, however, they appear both to originate and end
in the limestone, and present rather the aspect of detached lumps and
irregular processes than of veins.* So confused is this interference,
that a fragment of granite is often found entangled in the lime-
stone, and a lump of the latter will sometimes be found intruding
into the former. The minuter veins of granite are generally if
not always connected with the larger pieces, and they intersect and
reticulate the whole limestone as they do the schist, diminishing at
length to the thickness of a leaf of paper or a thread. But there is
a still more remarkable arrangement of the limestone and granite.
Parallel to the limestone bed or beds, and following every flexure
and contortion which it undergoes with the most perfect regularity,
are to be seen narrow lines rising above the general surface, and
accompanying the course of the bed through its whole extent. "On
examining them they are found to consist of a harder substance
which has resisted the action of the water, while the softer and in-
termediate parts, being of limestone, have been dissolved and washed
away.{ The fracture of the rock shows that these are the edges of
laminz formed of a reddish siliceous substance precisely similar to
that which constitutes the reticulations, and which from the contrast
of its colour to that of the blue limestone with which it alternates,
is always easily distinguished.

Having blown up a considerable portion of this rock, I am enabled
to say that it is of a laminated texture throughout, being a bed
of which the alternate layers are limestone and that siliceous red
rock which I consider as a modification of granite. A perfect notion
of such a limestone may be formed by recollecting the appearances

* Vide PlateJ 5. t Vide Plates 15, 16, 17.

DED

268 Dr. Mac Cuxttocu on the Geology of Glen Tilt.

of those laminated limestones which contain alternate layers of mi-
caceous schistus or clay slate.

There is yet one other disposition of these two classes of rock ;
this consists in minute points or fragments, if they may be so called,
of the same siliceous matter, inhering in the limestone, and which
from their smallness are scarcely to be detected, unless where
from having been exposed to the action of water they are
found to give a rough and echinated surface to the calcareous rock.
This appearance is very widely diffused through the whole extent
of the body of limestone hereafter to be described, as forming a
great portion of this district, wherever it is found in the vicinity
of the great mass of granite.

The singularity of these appearances renders it proper to dwell a
little on them, and to enquire into their connections and probable
origin. Saussure indeed has mentioned a transition from granite
to limestone, and, as there are some situations in Glen Tilt where
the limestone in contact with granite becomes so siliceous and in-,
durated as by degrees entirely to lose its mineralogical, and pretty
nearly its chemical character, so it is possible that he may have met
with some similar fact, although no very accurate notion can be
derived from his account of it and consequently no assistance ob-
tained from his observation.

As I shall have occasion to enter fully hereafter into the minera-
logical description of this and of the other rocks which occur in
Glen Tilt, and shall then vindicate the term granite, which as a
general term I have applied to it, I think it only necessary to say at
present that the mass of rock above described as traversing the
stratified rocks, is a portion of a more continuous one which may be
traced to the hills constituting the right hand or northern boundary

Dr. Mac Cuttocn on the Geology of Glen Tilt. 269

of Glen Tilt. It is not an independent vein. So far therefore the
geological connection, as well as the identity in mineralogical cha-
racter of the mass of granite which is approximate to the limestone
and schist with the granite mountains of the northern ridge, is in-
disputable. From this mass, processes or veins of different sizes
are seen to issue, until: they gradually terminate, as I before said,
‘in a thread. As long as these veins continue of a few inches in
breadth, their mineral character remains unaltered. As they dimi-
nish, however, the hornblende gradually disappears, although, in
the cases in which the vein traverses hornblende schist, this mine-
ral is increased in quantity, and the vein assumes rather a more de-
cided character of that rock which, as I conceive, is inconveni-
ently distinguished by the term syenite. But the vein of mixed -
quartz and felspar is the most common, and this, as it continues to
diminish in size ultimately becomes mere felspar, or else a com-
pound of felspar and quartz so intimate, that the magnifying glass
discriminates the particles no longer, and the whole is only distin-
guishable from common felspar by its peculiar fracture and superior
hardness. This circumstance, the varying composition of granite
veins, is not unusual, and it may be observed, among many other
places, in the Corpach bason of the Caledonian canal. Now, how-
ever inaccurate it may be in a mineralogical point of view to de-
signate the substance which constitutes the minuter veins by the term
granite, yet for the purpose of geological reasoning it is unavoid-
able, nay, proper, since the substances have an absolute continuity
or geological identity. It would be unjust either by a misapplica-
tion of terms, or an undue nicety in their use, to reject any geo-
logical argument which might be founded on such a fact as this.
The same is true of the siliceous lamine found in the limestone,

270 Dr. Mac Cuttocu on the Geology of Glen Tilt.

as well as of the detached pieces and small points, since they are ab-
solutely identical in composition with the smaller reticulations.

With respect to the limestone, it is subject to a variation of aspect
where it approximates to the granite which it is interesting and im-
portant to notice. The colour of the great limestone mass is lead
blue of various intensity, and its texture is almost universally
large grained and highly crystalline. It is true that in some few
instances it preserves this aspect in the situations described, but,
in the greater number of cases, particularly in those where it is pe-
netrated by the smaller veins and where the beds have undergone
an elongation or a contortion, the crystalline texture disappears.
It then assumes an appearance exactly resembling that of hornstone
or compact felspar, having a smooth texture, with a thin-edged
fracture intermediate between the splintery and flat conchoidal.
I may as well add here that the schist is often of an argil-
Jaceous, but highly indurated, character, and also that it often
passes into hornblende slate, and this (it is worthy of notice)
the more frequently as it approximates nearer to the granite.

So much has been said with respect to the origin of granite veins,
and on the mode by which their intrusion into the schistose rocks
which generally accompany them has been effected, that it is superflu-
ous to repeat it, since nothing new can be offered on the subject. By
whatever mode it has been produced, it is obvious that the same ex-
planation will apply to the case of the limestone which is ins
terstratified with the schist, as far at least as the veins are con-
cerned, although the fact itself be a new one. But how has the
alternation of lamine of granite with those of limestone been
effected ?

It is necessary here to anticipate that which will be fully
described, and, I trust, proved hereafter in a more proper place, the

Dr. Mac Cutrocn on the Geology of Glen Tilt. 271

original regular position and the posterior disturbance of these stra-
tified rocks. The limestone which is here visible, is a portion
of an enormous series of beds, which are to be found in a
regular position occupying the left ridge which bounds Glen
Tilt, interstratified with quartz rock and with different varieties
ef schist. This regularity of position is destroyed wherever
these beds come in contact with the mass of granite which oc-
cupies the right ridge before mentioned. Consequently, the
limestone involved in the schist and granite now under review,
is a portion of a bed the original position of which is perverted
and lost. Are we now to suppose that this bed of limestone was
originally deposited in its present form with alternating layers
of granite? Admitting that the reticulating veins have been the
consequence of a posterior intrusion, this cannot possibly be
true of the laminz, as independently of the difficulties, or im-
possibility as it may more properly be called, of such a pro-
cess, it is plain that the simultaneous flexure and contortion of
the laminated mass is the result of the disturbance produced by the
granite veins, and consequently that it was deposited before the
intrusion of those veins.* Must we then allow that there are
cases where granite, or a matter resembling it, has been deposited
like schist and bedded limestones from solution or suspension in a
fluid? In the mean time, however, the igneous hypothesis respect-
ing granite may perhaps allow of another mode of explaining this
appearance. It is conceivable that a mass consisting of alternate
layers of imicaceous or argillaceous schist and limestone, a com-
pound of which abundant examples are seen in the immediate
wicinity of the rock under review, might be so acted on by heat

* Vide Plates 16, 17.

272 Dr. Mac Cutiocn on the Geology of Glen Tilt.

as to admit of the conversion of its siliceous layers into the substance

now found interstratified in the limestone, while this latter resisting |
as it is well known to do, any change from the application of heat

under such circumstances, might undergo no other affection than

that softening which has led to its flexure and contortion.

The remaining appearances to be seen at this rock are more cu-
rious as adding to the unexampled confusion of the whole mass,
than as offering any thing very new to the geologist in addition to
that which has been already detailed.

Among the remaining substances entangled in this confusion, a
large vein of felspar is the most remarkable. Its course is not long,
nor does it appear to have any connection with the granite. It varies
in colour through this limited extent, being sometimes white, at
other times of a pink or dead lilac hue, and in some few places
greenish. ‘This latter colour seems to proceed from a mixture of
epidote, which mineral is found in other parts of the rock in thin
veins accompanying the granite and colouring the schist. Some
massive garnet is also to be seen involved among the other substances,
and it seems principally connected with the limestone. Ina few
cavities there occur crystals of flesh coloured calcareous spar, but so
incomplete from the narrowness of the spaces in which they have
crystallized, that I could not assign their figure. This I believe |
completes the catalogue of the minerals found in this singular place.

The granite is again seen crossing the river between this bridge
and Forest Lodge, and near it lies a body of quartz rock which is
evidently a continuation of some beds which may be observed in the
hill above.

About 300 yards below the Lodge it crosses the stream again, and
here the limestone is again mixed with it. A set of beds of a yel-
lowish and greyish colour, resembling some varieties of foreign

Dr. Mac Cuurocu on the Geology of Glen Tilt. 273

marble, and exceedingly indurated, may be seen occupying a space
of about twenty feet. Ifa careless view of these beds be taken, they -
will be found to offer what appears for the space of about ten feet;
to be an alternation of granite in a very regular disposition with
limestone. It has been mistaken for a real alternation. If this rock
be more’ carefully examined it will be evident that it consists of a
mere fragment, and that it is abruptly cut off where it nteets the
hill on the right, by abutting against the mass of granite. As the
lower end dips under the water, a clear view of that part was not to
be obtained when I examined it, but it appeared there also to be cut
off by a granite vein. Those parts therefore of the granite which
seem to alternate with the limestone can only be considered as
portions of veins, the disposition of which, like that of trap veins
in similar cases, has accidentally coincided with the direction of
the limestone beds. If granite does really occur in beds, I know
no reason to prevent it from alternating with limestone, but the
appearance here is much too limited, and too doubtful in its origin
to be admitted as an instance of such alternation. The gra-
nite which accompanies this junction may be seen in the bed
of the river for seventy or eighty yards, after which it disappears.
Three or four hundred yards of a blank alluvial space occur immedi-
ately after this, followed by a rocky space of about 200 yards.
This rocky portion exhibits the following alternation, granite, schist,
granite, limestone, succeeded by a general confusion of all these
substances, and the granite which is in general limited to the right
bank, now crosses to the left of the river. When*I say that there
is such an alternation, I do not mean that the several substances are
bedded in this order, the case to which the term alternation is more
properly applied. Itis particularly necessary to attend to this remark,

VOL. “Il; Qm

274 Dr. Mac Cutrocn on the Geology of Glen Tilt.

and to ascertain the real nature of this kind of alternation, since
it has been quoted at different times as proving a regular alternation
between granite and schist, the limestone, as it happens, having been
here overlooked. It is no further an alternation than because these
substances, which in numerous other instances are confounded and
irregularly mixed together, happen in this particular one and for a
very short space, to have assumed a disposition accidentally more re-
gular.* The question of alternation must rest on other facts than
these. A blank of about eighty yards follows this rock, and is suc-
ceeded by one of the most remarkable junctions of the different rocks
already described, which occurs in the course of the river. The
main body of this compound mass consists -of white limestone or
marble, without any tendency to that regularly bedded form which
is the general characteristic of the limestone in Glen Tilt. It is ac-
companied by a small portion of schist as well as by a mass of granite,
with both of which it is variously intermixed. The marble itself
is in most places of a pure white, a fine grain, and dry aspect, and is
extremely hard. In some places it is of an ochry colour, and is in-
terspersed by thin veins of the same substance, so as to resem-
ble some of the palest and worst specimens of that marble known
by the name of Giallo Antico. The schist which accompanies it is.
argillaceous and of a bluish colour, and the granite, both in the
larger masses and in the ramifications, bears so near a resemblance to
that formerly described that it is superfluous to describe it again.
The veins which traverse the marble, like those at the bridge above-
mentioned, are of various sizes and are placed in every possible di-
rection, but the ramifications are neither so numeyous nor so minute

as in that instance, nor is there any appearance of the laminated

* Vide Plate 14.

Dr. Mac Cuttocu on the Geology of Glen Tilt. 275

structure which occurs in the former. Where the marble is at the
greatest distance from the granite it differs little or nothing in hard-
ness or composition from ordinary specimens of this substance. But
wherever it approaches or comes into contact with the granite it be-
comes highly indurated, effervesces slowly with acids, and gives on
analysis a harge portion of siliceous matter. In other respects there is
no obvious change at the planes of contact, and the union between the
granite and limestone is so slight that the action of the water sepa-
rates them, The union of the limestone with the schist is much
more intimate. “Wherever the granite traverses both these sub-
stances together, which is generally the case where the schist is pre-
sent, such a confusion takes place, that the boundary of neither can
be defined, a troubled mixture and then a complete gradation between
these two rocks being the result.*

On the right bank of the river above this rock a bed may
be seen, consisting of a brownish hornstone, or rather a compact
felspar, with a character somewhat porphyritic. It is one of that
great variety of rocks associated under the general name of porphyry
of which frequent examples occur in the course of the Tilt on
both sides of the valley ; more than I have thought it necessary. to
mention. These are sometimes considered as veins, and sometimes
as beds; I believe that the former disposition is by far the most
common, but their real nature is often so difficult to ascertain that I
have been obliged to abandon the point in-despair. ‘The present one
appears to be a bed.

I have purposely avoided noticing the rocks on both sides of the
river which lie beyond its immediate bed, as they offer, on the
right side at least, a succession so mixed and so confused, that any
view of them which can be obtained in following the stream is nearly

* Vide Plate 19.
Qu 2

276 Dr. Mac Curroce on the Geology of Glen Tilt.

unintelligible. J may only say that schist, granite, and quartz rock of
different aspects, with occasional masses of porphyry, succeed each
other so frequently that the whole might be considered by those who
are prepossessed respecting systems of alternation, as a demonstrable
instance ofthis disposition. I hope to give a more correct view of
their connections hereafter. On the left bank I may also generally
remark that a succession of dark blue limestone, rarely interrupted by
schist, quartz rock, and granite, is seen on the left bank from Poll
Tarff down to this place, and even beyond it as far as Gow’s bridge.

An alluvial blank of about 800 yards follows this marble rock,
which is succeeded by 100 yards or thereabouts of granite; and
after 150 yards more of an alluvial space, a large mass of rock
for the space of 200 yards and upwards is found traversing
and obstructing the stream, so as to form a cascade. This very
irregular mass of rock consists of granite and quartz rock
united. The quartz rock is of a peculiar aspect, being of a bluish
colour, very uniform and compact and approaching near to
common quartz in character, but still shewing evident marks of
foliation. It is disturbed and intersected by the granite in a way
which I need not now repeat. A thin stripe of limestone and schist
may also be seen interwoven in the granite. Below the cascade _
there is once more a blank alluvial space of 100 yards, which is
succeeded by quartz rock for about the same space ; immediately
after which occur about fifteen yards of a yellowish and greyish lime-
stone or marble, very hard, and disturbed and traversed by granite
in the way already described. This is followed by a series of lime-
stone beds for about 200 yards, the first of which is blue and the
last five or six of a yellowish aspect: these are almost the first
limestone beds observed in descending the river which have the
same general dip and position with the beds of the mountain on the

Dr. Mac Cuttocu on the Geology of Glen Tilt. 277,

the left hand. But that position can only be called general, as in
every instance all particular or minute regularity disappears wherever
the limestone beds are found in the immediate vicinity of the gra-
nite. .Nothing very remarkable is to be seen between this place
and the entrance of the Criny. Near the point of confluence beds
of quartz rock are distinctly seen crossing the river, and dipping
under the limestone to which they are parallel.

Although various sections of the hills on each side are given by
the streams which fall into the Tilt, few of them are sufficiently
deep or explicit when singly taken to afford much information
about the structure of the hills. “he Criny however presents a
section of considerable importance, which, as it illustrates the views
that I shall hereafter give of the whole structure of this glen,
may as well be described here.*

The quartz rock which I have noticed as crossing the river, may
be traced through the chasm formed by this torrent, and it is found
reposing on limestone, which is immediately succeeded by argilla-
ceous schist. Iam uncertain whether there is not a thin bed of schist
interposed between the quartz rock and the limestone, and I have
represented such a one in the engraved section ; but it is not im-
portant, and the place is so difficult of access, while the confusion
produced by the waterfall is so great, that it is difficult to make
the investigation minutely. This alternate arrangement is found
immediately reposing on the granite, and the schist being the bed
in actual contact with the granite, is penetrated by veins precisely
similar to those which have already been described. The limestone
is here of a peculiar character, being mixed with quartz, some-
times in distinct concretions, sometimes’ in laminz irregularly

* Vide Plate 21. fig. 1.

278 Dr. Mac Cuttocn on the Geology of Glen Tilt.

alternating. ‘These veins originate in the mass of granite which
forms the mountain, and this observation is important, as I shall
hereafter shew that the granite seen in the Criny is a portion of
the great central granite mass which forms the whole range of hills
on the right bank of the Tilt.

From Glen Criny a succession of schist and quartz rock is to be
observed, extending till within a few hundred yards of Gow’s
bridge ; but the bed of the river being here inaccessible, we can
only obtain a general view of it. The last bed of quartz rock in
this direction is immediately followed by a bed of limestone, and
this again is succeeded by an alternation of beds of schist, lime-
stone, and quartz rock for some hundred yards below that bridge,
together with masses. of porphyry both of a reddish and a greyish
colour, but whether disposed in beds or veins I have been unable to
ascertain, though I imagine that they are beds, since they seem to
conform to the stratified rocks. As this collective mass presents
some interesting circumstances it will require a more minute de-
tail.

The position of the whole of these beds is regular, with two
very slight exceptions, and they occupy a space extending from 320
yards or thereabouts above Gow’s bridge to 200 below it.

We have: seen that all the irregularities of the beds take place
wherever the granite comes into contact. with them. Here there is
no granite present, but, on the contrary, the mass of limestone of
which these beds form a part, and which has hitherto been found
terminating in the bed of the river, is continued to the right hand
ridge, and may be traced high up in the hill, where the contact with
the granite takes place.* The only exception with regard to the

* Vide Section, Plate 20. fig. 1.

Dr. Mac CuLiocu on the Geology of Glen Tilt. 279

granite, is that of one solitary and small vein, of a grey colour, which
intersects the schist immediately above the bridge; the disturbance |
however produced by it is trifling. Another disturbance, although
small in extent, is very remarkable, though not unique, since I
have found a similar occurrence in Iona. Below the bridge on
the left bank a bed of white marble is seen surmounted by a bed of
hornblende schist. This is followed by a second bed of the marble
about two feet in thickness, of which the greater part is suddenly
cut off at right angles to the bed by a second mass of hornblende
schist, while the lower part continues in the same direction, but
bent, and of the breadth of only two or three inches. The lower
part of the mass of hornblende schist, which thus intersects the
marble, is also protracted in a thin plane continuous with the thin
part of the marble and lying above it, while the upper side of the same
becomes continuous with a regular and thick bed of the schist.
Between these two portions of the schist there is interposed a thick
bed of the marble, which is therefore included on three sides with-
in the hornblende schist, its outer extremity being cut through at
right angles by the schist. As the beds dip into the hill, the
further progress of this extraordinary arrangement cannot be
traced. A drawing accompanies this description, which words
can scarcely render intelligible.* The appearance now described
is interesting, since it is connected with phenomena of no very
uncommon occurrence, which have given rise to much controversy.
It is evident that both the prolongation of the limestone and that of
the schist bear a great resemblance to the veins, which, in the case
of granite, may be traced from a mass of that substance into the
neighbouring rocks: yet there is no doubt that both the lime-

* Yide Plate 22.

280 Dr. Mac Cuttocu on the Geology of Glen Tilt.

stone and the schist are stratified rocks. I have observed the same
appearances in clay slate, and they are frequent in the islands of
Scarba and Jura, where this substance alternates with quartz rock,
and where great contortions of these rocks have occurred. A more
remarkable example occurs in a rock which constitutes one of
the numerous beds of which Schihallien is composed. This rock
is a micaceous schist, containing imbedded fragments of granite
and of quartz rock, often of considerable magnitude. The larger
fragments of quartz rock are sometimes partially split at right
angles to its laminar structure, and these fissures are filled with the
substance of the mica slate, putting on the same pseudomorphous
appearance of a vein. I have found similar veins of red sandstone
in the limestone of Arran, and they have also been seen in
trap. But in a paper on Kinnoul IJ have described and delineated
a specimen from a very extensive set of appearances of this
nature, where a schist of the graywacke character becomes pro-
longed into ramifying veins in the interstices of a trap rock by
which it is broken and disturbed. It is unnecessary therefore
to enter on the subject in this place, but it will be sufficient to
say that such pseudomorphous veins must be considered as
portions of the strata, which, during their soft or softened.
state have been forcibly compressed and elongated into that
form. The appearance occurring at Schihallien might obviously
be produced by the mica while in-a loose state in water, falling
into and occupying the open spaces of the fragments deposited
with it; and, in a similar manner, rifts in limestone might have
been filled by the loose sand which formed the surrounding strata.
The explanation of the other circumstances which occur at the
junction of the limestone and hornblende schist which has given
rise to these remarks, will be as-obvious to those who shall inspect

Dr. Mac Cutrocn on the Geology of Glen Tilt. 281

the drawing as it is to me, and it is probably not very obvious to
any one.

It is not far from this place, and on the left bank of the river,
that a greenstone vein may be seen traversing the strata at nearly
right angles. It is the only specimen of genuine greenstone which
I observed in Glen Tilt, and it appeared to me to resemble those
veins which are found in Cruachan and in the neighbouring moun-
tains, where they also frequently assume a porphyritic aspect. Still
however they differ considerably in their general appearance from
those greenstone veins which are most usual in Scotland, and which
are found to predominate in the vicinity of the larger formations
of trap in the Western islands, and in many well known parts of
the continent of Scotland. |

The great mass of limestone which we shall hereafter find
forming the whole of the left boundary of Glen Tilt, is of a dark
blue colour, with one or two exceptions which I have already
described in the progress down the river. But the beds at this
place are of various colours, and offer some of the most beautiful
ornamental marbles which Scotland has yet produced.*

The basis of nearly the whole is a white, rather larger grained,
and crystalline marble. Beds of this variety occur in a pure state,
and of considerable dimensions. But as all these marbles contain
more or less of mica, with which substance they are interstratified,
the white colour is seldom pure, being mottled with the slight grey
tint which mica in similar cases always produces. It cannot there-
fore be considered as a statuary marble, since modern artists, ac-

* Having pointed out the circumstance to the Duke of Atholl two years ago, quarries
are now opened in them, by which the numerous varieties which they contain have been
i
more completely brought to light than they could have been by the operation of a mine=
ralogist’'s hammer.

WOus Tit QN

282 Dr. Mac Cutztocu on the Geology of Glen Tilt.

-quainted with the beautiful stone of Carrara, have confined their
labours to this more perfect variety. It is however perfectly appli-
cable to various architectural as well .as ceconomical objects. A
marble perfectly similar to it has lately been imported from |
America for the same purposes, to many of which its greyish hue
and low tone of colour are more applicable than the dazzling
white of Carrara. It is of a larger grain and a more compact tex-
‘ture than the Pentelic, with which the beautiful and interest-
ing remains imported by Lord Elgin have lately made us acquainted.
But the Pentelic marble, like that of Glen Tilt, contains mica,
and from this contamination arises its fissile nature, to which we
unhappily owe so much of the injury which these wonderful
works have suffered. When polished, the two can scarcely be
distinguished from each other; the difference in the size of their
grains disappearing, and the grey and watery stains, with the
brown stripes of the micaceous laminz, equally «characterizing
both.

The discovery of statuary marble in the British dominions has
been long a desideratum, but having already in the present volume
discussed this question, I shall only briefly remark that how much
soever we may admire those wonderful sculptures by Phidias which
have been executed in a marble scarcely differing in colour or quality
from this of Glen Tilt, we are very well assured on examining the
progress of art in Greece, that the marble of Pentelicus was only
used in the deficiency of a purer and more uniform stone, and that
it was abandoned when later discoveries had made the sculptors of
that country acquainted with a better class of marbles. It would
be a fruitless attempt to introduce the marble of Glen Tilt, or even
those whiter varieties which Scotland produces, in competition
‘with the exquisitely beautiful and easily wrought stone of Carrara,

Dr. Mac Cuttocn on the Geology of Glen Tilt. 283

as long as these quarries remain accessible to us. For that higher
class of sculpture on which the powers of genius are exerted, the
proportion between the price of the wrought and unwrought
article, (to use commercial phraseology) is so unequal, that no
difference in the value of the raw material can compensate for even
the most trivial defects in its quality. But there remains even in
the class of the fine arts a great number of uses to which the
marble of Glen Tilt might with advantage be applied. Such are
all those works in architectural decoration, in which absolute
whiteness and uniformity of colour, are not only unnecessary, but
from their dazzling effect even injurious. The subdued tone and
slight air of antiquity given to this marble by its stained and
unequal colour would in these works render it of the greatest use.
Its durability for the purposes of interior architecture must also be
equal to that of Carrara, although there is little doubt that when
exposed to the action of the weather it would like the Pentelic be
liable to corrosion in those parts which abound in mica.

Besides mica, steatite and noble serpentine are found mixed with
the white marble. The colours of these substances offer various
gradations from bright yellow down to the darkest sap green.
It is by these admixtures that the green and white marbles which
form by far the largest portion of these beds are produced. The
colours are so variously mixed, blended, and dispersed throughout
the stone that numerous varieties are the result; and these are
further increased by the occasional presence of dark lead blue.
This mixture of serpentine with marble is by no means uncommon
in Scotland. On the contrary it may be said that all the white
marbles found in this country contain it in a greater or less degree.
It is common in the white marble of Sky and in that of Balahulish.
In that of Assynt it is more rare, but it occurs also abundantly in a

ZN 2

284 Dr. Mac Cuttocu on the Geology of Glen Tilt.

white marble which I found in Glen Fernat, not far from the
junction of the Brerachan with the Airdle. The well known
ancient green marbles owe that colour to the same admixture,
which indeed in the Egyptian green and the Verde antico, is such
that the calcareous matter is overpowered by the serpentine. The
aspect of the green marble of Glen Tilt is however perfectly differ-
ent from that of any marbles ancient or modern which have yet been
wrought, and it offers therefore a valuable addition to the arts ‘as
well as a new commodity to the list of our mineral productions.
IT may add that, with a similarity of composition, many specimens
bear a considerable resemblance both in character and colour to
some varieties of the Cipolino of the Italians. “Iwo other distinct
varieties of marble occur where the calcareous beds terminate. The
one is of an uniform ochre yellow, but of a much paler tint than
the giallo antico; the other is of a flesh colour graduating into dark
blue, but neither of these beds is of great magnitude.

The extent of the limestone which I have now been describing is
considerable. ‘The mass is of great thickness, and from the obliquity
of its section a very large horizontal surface is exposed. As the
beds run towards the north they may be traced to a considerable
distance up the hill on the right of the river, but dipping to the
south they plunge into the opposite hill and disappear. Indepen-
dently of the steatitical matter which is mixed with this rock, some
interesting minerals are found imbedded in it. The beds where
they come in contact with micaceous schistus contain so much mica
that this latter becomes at length the predominant substance, and
there is then a perfect transition from micaceous schist to marble.
In these cases it is raised in thin flags of great extent; between
these flags there are often seen beds of steatitical clay, of a pure
white or greenish hue, and often of considerable thickness. In the

Dr. Mac Cuttocn on the Geology of Glen Tilt. 285

same situation may be seen thin beds of a compact pale green
and transparent steatite, and irregular lumps of the same substance
are frequently found dispersed about the beds.

It is rare to find distinct pieces of noble serpentine of any mag-

nitude, but they are also met with, and of a transparency and green-
ness equal to that of the well known specimens from Iona.
» Talc of various colours, white, lead-blue and green is likewise met
with among the marble beds, but in small quantity: and asbestus,
although it 1s seen here and there in considerable pieces, may also be
considered rare. But it produces abundance of tremolite, and offers
some interesting and uncommon varieties of that beautiful mineral.

Of these, the first is fibrous and very compact, having a slight
purplish tinge, particularly when viewed according to the axis of its
crystallization. It is imbedded in the rock, with which it is perfectly
compacted, presenting on fracture a small stellated or a longer
radiated appearance, and giving a peculiar character to the marble.

The next variety consists of a congeries of regular prismatic
crystals, varying from a tenth to a sixth of an inch in diameter.
These are seldom radiated, but most commonly form a dense mass
of which the crystals are irregularly interwoven together, and
sometimes curved. ‘Thin beds of this are found between the
marble beds, and in some cases the crystals have shot in cavities so
as to present terminations, which, however formerly complete, have
been spoiled by the action of the water on them.

It is well known to mineralogists that many substances when found
in the earth are in a soft state, and only acquire induration when
removed from their native beds. If we are to believe Patrin the same
is true even of the beryl. It is so with the tremolite which I have
now described, which is exceedingly soft and flexible when first
up, but hardens after some days of desiccation, The asbestus taken

286 Dr. Mac Cuttocu on the Geology of Glen Tilt.

which I found here is likewise so soft that it may be wrought into
a paste with the fingers, but it acquires in a few days a hardness
equal to that of fir wood. I have observed the same fact in the
disthene which I collected at Boharm in Bamffshire. It is worthy
of remark that the reapplication of water does not restore these
minerals to their flexible state. We have yet to learn the chemical
explanation of this circumstance.

There is no novelty in the fact I have here brought forward,
but sufficient attention has not perhaps been paid in geological
writings, to this differing condition of many strata as they exist in
the earth, and after they have undergone that change to more
perfect induration which they acquire after being removed from
their native places and exposed to the air. With regard to many
rocks used for ceconomical purposes it is notorious even to work-
men. It is easy to see how this circumstance affects many of the
reasonings which have been brought forward on the consolidation
of strata; a condition of which we see perpetual examples before us,
without any ground for supposing that the agency of heat was
conducive to that end, and in circumstances indeed where no agency
of heat can be imagined capable of producing the complicated
effects which have resulted. We are too little acquainted with the
chemical laws which regulate the aflinity of earths in a state of
extreme division, to decide on results which may or may not be
produced from either solution or suspension in water. One solitary
fact well known in the potteries showing the strong affinity which
exists among earths in such a state of extreme division and suspended
in water, is sufficient to suggest to us the possibility of affinities
still more intense existing among earths in similar circumstances,
when their proportions perhaps are different, or where, in addition

Dr. Mac Currocu on the Geology of Glen Tilt. 287

‘to a more minute division, many of them may perhaps also be in
a state of solution. On a small scale indeed examples of stony
matters so formed are not wanting in nature. Such are the hard
deposits of calcareous and other matters in water pipes, and in
vessels at no greater temperature than that of boiling water. It
is easy to see in the case of the semi-indurated strata, and of the
‘soft minerals above described, how the further abstraction of the
water in which these affinities were first brought into action, may
by increasing them in consequence of the nearer approximation of
the earthy particles, induce that stony hardness which these sub-
stances acquire in drying.

A third and more beautiful variety of tremolite is also found
here. This like the last forms thin beds interposed between those
of the marble, and occasionally also entering as a constituent part
into. the stone. It is that well known variety which so much
resembles spun glass, that this comparison forms the best description
that can be given of it. It is generally of a pure white colour,
and is radiated in stellated forms varying from an inch to two feet
in diameter, and exhibiting specimens of uncommon magnificence.
I could not perceive that.any of the specimens of this variety were
so decidedly flexible as the latter, although they were taken from
the bottom of the river, but there was still a very sensible difference
in their power of cutting the hands and entering into the skin
when first taken up, and after they had been kept for a few days.

More rarely the same fibrous and silky variety is found passing
‘through all the shades of colour, from a pale to a very dark sea-
‘green, and these latter specimens are particularly marked by the
crowded and beautiful groups of their small stellated radiations.

At no great distance from these beds and in a similar position, a
fourth and hitherto undescribed variety is also found, constituting a

288 Dr. Mac Cutiocu on the Geology of Glen Tilt.

bed of two or three feet in thickness. In its general aspect it so
nearly resembles a granular quartz as to be at first sight difficultly
distinguished from it. As it produces no effervescence with acids,
it probably contains no great mixture of carbonate of lime, and may
therefore be considered as a granular tremolite. It may be distin-
guished from quartz by its superior lustre, translucency, and specific
gravity, as well as by its inferior hardness. The sp. gr. of the
specimens which I tried was 2,840.

A fifth variety is found in the same place, but without so very
marked a character as that of the one preceding. It is foliated, with
a slight tendency to a fibrous structure, and forms large concretions
in the marble. Its aspect is vitreous, and it is of a greenish grey
colour.

Another modification of this beautiful mineral which occurs here
can scarcely be considered of sufficient importance to constitute a
mineralogical variety. It splits into thin lamiiaz, of which the flat
surface has the splendour and almost the uniform smoothness of
white satin, but on examination it is seen to consist of very minute
fibres of tremolite interfoliated with very white and compact car-
bonate of lime. Some specimens are again found which seem to
consist of a mixture of tremolite and schiefer spar, a substance which
is also found although but rarely, among the calcareous beds.

The various forms indeed under which the several mixtures of
tremolite with the surrounding rocks occur are such as to elude
description, and not a little to puzzle a mineralogist. I shall only
enumerate two more of the most remarkable. One of these is a
compact schistose rock in which the union of the tremolite with the
limestone is so intimate that it can only be distinguished in the
first instance by its hardness and specific gravity, as the eye cannot
detect the mixture. In the other the tremolite is mixed with a kind

Dr. Mac Cuttocn on the Geology of Glen Tilt. 289

of steatitic slaty marle, very friable, of a snow white colour and
great specific gravity. .

Associated with this limestone and ina similar position, I also
discovered beds of sahlite, a mineral of considerable rarity in this
country. These vary in thickness from two inches to a foot
and more, and are sometimes intimately mixed with thin lamine
of the fibrous variety of tremolite. This mineral, from its superior
hardness, resists the action of the water of the river better than
the limestone does with which it is interstratified, and may there-
fore be distinctly traced projecting from those beds of which tit
calcareous portions have been more or less worn away.

The beds of sahlite may be seen extending for a space of from
fifty to a hundred yards along the bank of the river at the same
place. Considerable variety of aspect occurs throughout their
course, from a greater or less intermixture of calcareous matter with
the pure sahlite. Thus, like the more common specimens of this
mineral it sometimes effervesces with acids, while in other ‘cases
it appears to contain no uncombined calcareous matter. When
it is unmixed it resembles at first sight the whiter varieties of
felspar, exhibiting a large platy fracture, and a similar lustre.
In the angle of its fragment as well as in its specific gravity,
hardness, and habitudes with the blow-pipe, it perfectly resembles
the better known varieties of this mineral. As it becomes more
and more mixed with the calcareous matter its platy fracture first
becomes less regular and gradually disappears, the mixed mineral
however still retaining a specific gravity greater than that of the
neighbouring limestone. Its sp. gr. varies from 3,153 to 3,246, the
most purely lamellar being the lightest. It is invariably white with
a slight tinge of grey.”

* | may here add that I have found.this mineral in Glen Elg, and in a similar situation,

but exhibiting different colours, the predominant variety being snow-white, and the mare
rare one green: I have also found it in great variety in Tiree and Harris.

VOL. Ill. 26

290 Dr. Mac Cuirocn on the Geology of Glen Tilt.

I should not however conclude this account of the minerals
which occur in this part of Glen Tilt, without mentioning that
fibrous limestone is also found in some of the rifts, showing a little
of that pearly and changeable lustre, for which the satin spar is so
remarkable. .

I have thought it unnecessary in describing either these or the
other rocks which I haye examined, to particularize the several
anomalous mixtures of substances which are found about them,
since they are extremely partial and generally limited to the vici-
nity of the junctions. They all appear to be of a mechanical
nature, or at least to have resulted from the same causes which
produced the several disturbances already described, and they offer
no particular instruction, while at the same time they can scarcely
be defined by words.

Quitting these marble beds and descending still the course of
the Tilt, schist, quartz rock, and limestone, are seen alternating
for about 500 yards. In one place a bed occurs in the quartz rock,
forming a regular part of the series, but composed of the con-
stituents of granite, these being sometimes disposed in a granitic
manner, and sometimes possessing the foliated texture of gneiss.
This is followed by a schist, which seems intermediate between gneiss
and micaceous schist, having the aspect of the latter with its:
shining surface and even foliated structure, but shewing in the
cross fracture the grains of felspar which belong to the former.

Proceeding further on, a great series of these thin beds may be
observed, of which some on being broken present the aspect of
true granite, inasmuch as the mica is irregularly placed and the
lamine of the rock, however foliated in position, are by no means
foliated in structure. A fragment so broken as to be divested of its
external flat form, would be considered as a fragment of granite

Dr. Mac Cutrocu on the Geology of Glen Tilt. 291

since it must be esteemed an essential character of gneiss that the
mica should possess an arrangement, at least so far parallel, as to
give the appearance of a foliated structure. r

As whatever view we can take of this occurrence is followed by
important consequences, it is necessary to consider it somewhat -
more particularly, and I shall first examine that case in which the
‘gneiss is found alternating with the schist. We have already seen
in numerous instances, that great anomalies take place in the aspect
of the schistose rocks, as well as of the limestone, wherever they
approximate to the granite and are traversed by granite veins, I
must therefore premise that no such veins are seen in this place.
The mass of granite is here indeed removed to a considerable dis-
tance, and the schistose beds are perfectly straight and undisturbed.

The general series consists of mica slate, alternating in a very
irregular manner with hard argillaceous schist and quartz rock, and
with a few beds of limestone. With these beds is found that mi-
caceous schist which contains felspar, and which will probably
be considered by most observers as a modification of gneiss. If
then it be called gneiss, that rock alternates with quartz rock, clay
slate, mica slate, and limestone, an anomaly at variance with the
almost universally received doctrines respecting precedence in rocks,
If we now turn our attention to those specimens which have the gra-
nitic aspect, I may remark that, however decided this character may
be in some particular points about this place, I shall here lay no
stress off it, as better examples can be adduced from the hills at no
great distance. Although the granite, in the instances which I shall
enumerate, occupies but a small space among the laminz, its texture
is perfectly granitic, and bears not the slightest resemblance to that
of gneiss, since the mica is placed in all directions, and the portion
in question, if detached from the neighbouring parts, could not be

202

292 . Dr. Mac Cuxtocn on the Geology of Glen Tilt.

‘distinguished in the generality of hand specimens from genuine
‘granite: at the same time I must add, that it bears but little resem-
blance to veins. The neighbouring rocks furnish abundant ex-
amples of. ordinary granite veins, which are readily distin-
guished from the present appearances by the decision of their
junctions, while in this case a regular gradation exists between the
‘granite and the schist, and no boundary to the former can be as-
signed. ‘The appearance which I have now described is not limited,
as I have just said, to this place: other examples of it may be found.
‘Besides the loose specimens of it which are to be observed among
‘the transported blocks on the hills which bound the left side of the
valley, it is also of frequent occurrence through a large tract which
extends from Blair to Dalwhinnie, and thence to the head of the
‘Spey. The specimens seen in this direction frequently exhibit va-
rious and repeated alternations of granite and schist, from the thick-
‘ness of three or four inches down to that of a quarter of an
‘inch. The tract in question is wholly, or in a great measure, com-
posed of hard argillaceous schist, graduating into schistose quartz
rock and more rarely into micaceous schist, with granite veins dis-
‘persed here and there «through it. Between the laminz of these
‘schists the granite is found graduating into the schist, many varie-
‘ties of coarser or finer texture appearing in rapid succession
‘in'the space of a few inches. [tis only by the comparison of a
‘number of specimens that the true nature of the rock is discovered,
‘and it affords a curious example of the facility with which false
‘conclusions may be formed on this intricate subject. However pa-
rallel the lamin of granite may be to those of the schist for a
certain space, they invariably quit that direction when the specimen
is of sufficient magnitude, and may be seen holding an. oblique
‘course through these laminz, often indeed becoming true granite

Dr. Mac CuLztocn on the Geology of Glen Tilt. 2983 -

veins in their course, and even crossing the layers at considerable
angles. A rock observable at Garviemore illustrates this accident
well. Here the transit of the granite vein through the schist is at
right angles, and is attended with a flexure of the layers on each
side of the vein, in a curve directed from the thickest to the thinnest
part of it. At each side of the vein the granite passes from it be-
tween the lamine of the schist, producing a partial effect similar to
the more extensive one above described, and which has doubtless
owed its origin to a similar cause. |

The other case which I reserved for consideration, is that where
similar beds of granite are found alternating with, and graduating
into quartz rock. This alternation is visible in the bed of the river
not far from the entrance of the Mark. But a much better
‘instance occurs in the hill,of Grianan on the right of Glen Tilt,
-where the transition from the quartz rock to the granite is so per-
fect that the boundary cannot be defined. I have met, with similar
appearances in the vicinity of Dalnacardoch,

In.a paper which I presented to the Society last year, I described
among several varieties of quartz rock, that, perhaps the most common
of all, in which grains of felspar are found mixed with grains of
quartz, neither of them being crystallized ; and I then pointed out
the distinction between this rock and granite, attempting to shew
that it was a recomposed rock, and that it had been formed from
the wearing of more ancient granites. Among the several tran-
‘sitions of quartz rock into mica slate, clay slate, &c. I did not
notice. this transition into real granite, as I had not then met with
this appearance :. it will add one to the number of those transitions.
It will at the same time be obvious, that it can in no respect affect
the account which I then gave of the nature and connections of
quartz rock, Onothe contrary, as J have shewn that this.rock be-

294 Dr. Mac Cuttocu on the Geology of Glen Tilt.

longs to the same order of rocks as mica slate, and clay slate, it
will only serve to point out their concurrence in another common
circumstance. It is perhaps almost superfluous to say that the
transition, which I am now describing, of quartz rock into granite,
is by no means a dubious one, and that it does not bear the least
resemblance to the common variety above referred to, which has so
often been mistaken for granite. It is perfectly crystallized through-
out, the felspar, the quartz, and the mica, having that aspect and
relation to each other which cannot for a moment be mistaken by
any one acquainted with the characters of rocks. ‘The aspect of the
mica alone is so remarkable, and so different from its appearance when
found in quartz rock, that it is sufficient of itself to distinguish this
modification from every other. Before quitting this subject it is
necessary to remark, that one of the transitions between the granite
and quartz rock takes place at the junction of the latter with the
great body of granite.

I have been thus particular in describing this singular rock, be-
cause it has often been confounded with gneiss, from which it is
strongly distinguished in its mineral character, and because it is
important that a substance of so much consequence in the system of
rocks as this is should have its relations accurately ascertained, and
should not from laxity of definition be introduced into a series ©
with which it has no geological connection. Many of the West-
ern islands offer examples of it in its most genuine form.

From the point last described, following still the course of the
stream, nothing is seen for the space of a mile and upwards, but a
continued succession of the same varieties of schist. These rocks are
also found occupying the hills on both sides of the glen, as far as
they are within sight of the river.

If there are any other remarkable varieties, or any peculiar cir-

Dr. Mac Cutiocn on the Geology of Glen Tilt. 295

cumstances connected with the schist which forms the bed of the
river throughout this space, they were concealed from me. The
channel becomes so deep and the sides so clothed with wood, that
it is scarcely possible to examine the banks; and the bed of the
river itself may safely be called inaccessible during nearly the
whole of its remaining course to Blair. . Within about two miles
of Blair, however, at a point which is marked by a cascade
and a small bridge, a large mass of yellow marble is seen crossing
the river. It is, like that before described, of an uniform ochre
colour, and like it, applicable to architectural uses. Lower down,
near the junction of the Fender, where there is again access for a
short space, the great body of blue limestone is found. This
may be traced across the grounds of Blair, and in the bed of the
Banavie, where it exhibits those minute reticulations of siliceous
matter which I have already described. From hence it is again
to be traced to the opposite side of the Garry, where it forms a
great part of the green hill of Tulloch. On this hill, at Invervach,
many of the beds are white, and resemble those already described
at Gow’s bridge, being interlaminated in a similar manner with
steatitical clay, and accompanied by mica. But I have passed my
proposed boundary.

Having anticipated no more of the description of the two ridges
which bound Glen Tilt, than was necessary to understand the
nature of the rocks which are seen in the bed of the river, I must
now return to them, taking up the right hand ridge, or north
side of the glen, at the place where I have now stopped.

That portion of the ridge which lies from Blair to Gow’s bridge
is so encumbered with wood in some places, and offers so little
interest in others, that I am content to pass it by in a superficial
manner, particularly as its more minute examination would throw

296 Dr. Mac Curttocn on the Geology of Glen Tilt,

no light on those interesting appearances in the bed of the Tilt
from which it is so remote, and which are the principal objects
of this paper. Itis sufficient to say in general, that it consists of
the several varieties of schist already noticed, which will doubt
less be found associated both with quartz rock and limestone,
and reposing somewhere on granite, as the other parts which I
have really examined are found to do.

On the declivity of the hill above Gow’s Bridge the schist and
quartz rock may be seen irregularly alternating with each other and
with the limestone. On the hill Stronna’Chro the green marble
beds are found at a considerable elevation, associated, as they are
below, with these rocks, being in fact the continuation of that series
of beds, the dip of which however various in the quantity of the
angle, is always in a southern direction. A little higher in the
hill the granite oceurs: it is of a red colour, and precisely similar
in character to that which is observed throughout the bed of the
Tilt, and which I have already described.

The burn Aldcriny having worn a deep channel in the rocks, it
is easy to see the granite for a considerable extent zz situ; and its
connections which are visible at the lower part of the channel
of the Criny having been described before, I need not here repeat
them.

The granite continues along the ridge to Grianan, and is ac+
companied by quartz rock, of which the connection with the gra+
nite is unintelligible in the hill, however it may hereafter be ex=
plained by comparison with other observations. This rock itself
is of a very compact and somewhat transparent quartz, containing
irregular grains of felspar: it breaks in a flaky manner, and ap~
pears to consist of beds extended in a north-easterly direction, and
dipping to the westward of north. It is impossible, however;

Dr. Mac CunLocu ox the Geoiogy of Glen Tilt. 297

either here or. in any other instance which I have met with, to
give a correct description of the dips of the schistose rocks which
occur in the highland mountains, without running into endless
details, since they are perpetually varying. It is perhaps fully as
useless as it would be laborious to the observer and tiresome to
the reader. These beds, at least for a short space, lie on the north-
ern bank of the granite mass, and-stretch away in a south-east line
to Cairn na ’Chlavhan and Connalach more, which elevations
consist, entirely of quartz rock. The granite continues still visible
to the eastward in the direction of the hills, but ceases to be red.
It is now grey, and shews a slight tendency to a foliated structure. ;

This peculiarity of structure, imperfectly as it is marked, is an
object of curiosity. I have already described a quartz rock as
passing by a regular transition to granite, and here the granite in
the vicinity of the quartz rock is found to have a foliated tendency,
a tendency which not improbably unites it at some point with the
quartz rock, although I did not discover that point of perfect
transition. On the same summits I also picked up a specimen of
genuine gneiss, but did not discover whence it had come.

The hill of Gonnalach beg shews a.summit of granite, but it is
a small space surrounded by quartz rock. The granite here passes
into a variety which, with the same general aspect, contains crystals
of hornblende. .'The two varieties are perfectly continuous, as con-
tinuous as the red and the grey, which | have just described.

Here then we have, as in numerous other instances, a con-
firmation of the geological identity of common granite, and of that
which is considered as a separate substance by the name of Syenite.
However distinct these two rocks may be considered as cabinet
specimens, there is no distinction in their habits and connections, nor
have we any reason to believe that the zras of their formation are

VOL. Lt. 2P

298 Dr. Mac CuLtocn on the Geology of Glen Tilt,

different. It is also no less inconvenient than unnecessary and im-
proper, that the designation of a granite vein, when on entering a
schistose rock it acquires hornblende, should be changed from
granite to syenite. ‘This mineral ought to be regarded as accidental,
and whether present or absent it makes no alteration in the rock
considered as a mass, nor can it alter or affect the validity of any
geological reasonings which may be deduced from the relations of
the granite in which it is found, to other rocks.

It has with equal want of proof been said that granite of dif-
ferent aspects belonged to different epochas or periods of forma-
tion, and we thus read of newer and older granites, as if mineralo-
gists had established criteria by which these several varieties could
be referred to a prior or posterior era. If the connection of ‘trap,
sometimes with primary rocks, sometimes with those which con-
tain animal remains, gives a support to these speculations where the
rocks of this family are concerned, there are no such connections
between granite and the surrounding recks known as to justify them
in this case.

In this place as in many others different varieties of granite are
found ‘together, not forming veins nor distinct masses, but gra-
duating into each other by an indistinct transition. The several
colours succeed each other at the same time with as little order as
do the aspects and proportions of the constituent parts.

The quartz rock appears again to the eastward of Connalach beg,
similar in its aspect to that one last named, and after continuing for
a few hundred syards, it is succeeded by another variety of granite
of a small grain and flesh colour, which forms a large mass of the
mountain.

A superficial view of this perpetual repetition of granite and
quartz rock, would lead ‘to the false conclusion that these two rocks

Dr. Mac Cuxrocn on the Geology of Glen Tilt. 299

alternated, and that quartz rock was, as it has too often been con-
sidered, a modification of granite. This supposition I have else-
where shewn to be unfounded, and that this rock is a member of
those schistose formations which are found reposing on granite. I
shall prove hereafter, that in this instance also the apparent alterna-
tion of the quartz rock is a deception, and that it is, like the lime-
stone and the schist with which it really does alternate, superimposed
on the granite.

I have in former papers presented to the Society, shown that the
polarity of granite, or its power of affecting the magnet, is by no
means so rare an occurrence as it was supposed. I may add to
these observations, that almost all the granite found here possesses the
same properties. But as this is a question involving some important
considerations which would interrupt the chain of the present
investigation, I shall consider it in a separate paragraph at the end
of this paper.

As I reserved the mineralogical description of the granite which
is found in the bed of the river in contact with the schistose rocks,
till I had described the larger masses with which it is connected, I
shall now describe it, as well as such other varieties as appear
worthy of particular notice. I may here also say, that if a term
be required for the purpose of distinguishing it from that granite
which does not contain hornblende, it may be called syenitic gra-
nite ; in treating however of its geological relations, I do not think
it necessary to adopt so long a term, which it will be sufficient to
use Whenever it is requisite to distinguish its peculiar character as a
compound rock. One advantage to be gained by the use of such
a term will be, that the term granite will thus become a sort of
generic term, including species, or varieties, which differ from the
compound of mica, quartz, and felspar, and of which there are

2p2

300 Dr. Mac Cuntocn on the Geology of Glen Tilt.

mstances to which no distinct denomination has been applied, as
this term of syenite has been to those which contain hornblende.
And since the granite of mica, felspar, and quartz, is sometimes
found to contain here and there a solitary crystal of hornblende,
with which in a series of gradation those varieties in which horn-
blende at length prevails to the exclusion of the mica are connected,
it is impossible to define the point at which granite is to end and
syenite is to begin: there is no difficulty in modifying the appli-
cation of the adjective term. But another, and the principal ad-
vantage arises from the limitation of the term syenite to a rock of
which the mineral character is much more constant, at the same
time that it is in general very strongly distinguished from granite
in its appearance. In its geological connections also it differs so
widely that it is absolutely necessary to remove all chance of their
being confounded together, since this rock is connected with the
trap family, and is found in a position in which neither granite
nor syenitic granite has ever yet been seen, namely, incumbent
on the rocks of secondary formation.

To proceed to the description of the rock’ at the junctions for-
merly described. It consists chiefly of high red felspar and white
quartz, of which the latter is generally in the smallest proportion,
the compound mass containing obscure crystals of dark green horn-
blende. These are seldom in large quantity, more commonly
they are thinly dispersed through the rock, and not seldom even in
the largest masses of rock they are altogether absent. I have not
observed mica,in any of the granite at the junctions described,
but in several parts of the hills-the same rock, or one not to’ be
distinguished from it except-by this circumstance, is found to con-
tain mica together with hornblende, which latter not unfrequently
becomes excluded altogether and the simplest form of granite re-

mains.

Dr. Mac Cuttocn on the Geology of Glen Tilt. 301

The various granites described as occupying the principal parts
of the ridge, are also mixtures of quartz, mica, and felspar, dif-
fering however as much in colour and texture as they do in struc-
ture; to describe such varieties is not possible, were it useful.
The chief varieties of the syenitic granites are found on the slopes
which descend to the Tilt, and they are almost invariably of a grey
and black colour, from the predominance of the hornblende: their
texture is as various as their'shades of colour, the crystals of horn-
blende being sometimes very large and decided, and imbedded as
it were in a paste of quartz and felspar, while in other extreme
cases the minuteness and mixture of the several ingredients is such,
that the constituents can scarcely be discerned. In these cases the
specimens have sometimes the fallacious appearance of the green-
stones of the trap family. ‘They may, however, be distinguished
from these by attending to the white ingredient, which frequently
consists of quartz with little or no felspar, while in all cases it con-
tains quartz, a substance which is but rarely found in greenstone.
They may generally also be recognized for what they really are, by
tracing them for some space, when their characters will be found
to become more conspicuous, either by the enlargement of the
constituent parts, or by the admixture of mica, a substance which,
except incidentally, is not found as an ingredient of greenstone
properly so called. These rocks, like common granite and gneiss,
frequently contain epidote as a constituent incidental part, and in this
also they are distinguished as well from that syenite to which I pro-
pose to limit the term, as from the greenstone of the trap family,
since epidote is but very rarely found among these latter rocks. They
are equally distinguished from them by the frequent presence of
another mineral which, as well as the former, is peculiar to the
older rocks, Sphene. This is found in considerable abundance,

302 Dr. Mac CuLtiocu on the Geology of Glen Tilt.

minute, but well crystallized and dispersed throughout the stone.
It is by no means uncommon in similar rocks in Scotland, and oc-
curs, among other places, in Criffel as well as in Braemar; and I.
may here add, that I have found it in specimens of Egyptian gra-
nite which contained no hornblende. I think it unnecessary to
enter into any further details. of this nature.

It is not far from the granite which I have now described, that
the quartz rock with the transition»into granite which I have
already described, occurs, and it is not necessary to make any
further observations on it in this place. At Craig Crocha the gra-
nite again makes its appearance; and here, as in other places, it
passes by a gentle gradation into syenitic granite, that is, it con-
tains. crystals of hornblende.

It is quite superfluous to continue the details of the structure of
this ridge with the same minute accuracy, as they will be found
little else but a repetition of those which have preceded. It
is not however the less important to give a general viem of the
whole, and I shall therefore state it to as wide a range as is ne-
cessary for understanding the structure of Glen Tilt, and the true
nature of the interesting appearances there visible.

Ben Dearg may properly be considered as. the most conspicuous
portion of the granite which forms the basis.of this range of hills. It
is connected with the right ridge of Glen Tilt which I have now
been describing, by a succession of granite and quartz rock, exactly
similar to that already noticed. Pursuing the direction of the country
across the Tarff to Cairnmuir and the head of Dee, the same succes-
sion gradually unites the granite of this. tract to that which forms
Cairngorm and Ben Avon, the great central granite of the Grampian.
hills, and the most extensive tract of this rock in Scotland.

There is no reason then to doubt that the granite which forms the

Dr. Mac Cuxxoca on the Geology of Glen Titi 303

right ridge of Glen Tilt is part of this great mass, and it in fact con-
stitutes its termination in a southern direction. ‘To ascertain its con-
nection with the quartz rock, it is necessary to compare numerous
observations made on the slopes of the hills, and in the channels of
the torrents where such connections are visible. I have already
mentioned the very conspicuous junction visible at Glen Criny, and
it would be tedious to repeat the rest of the observations from
which the general conclusion.is drawn. That general conclusion is,
that the quartz rock is superimposed on the granite,* and that every
instance of apparent alternation in these rocks may be resolved into
this. The confusion which arises in the disposition of these rocks
depends on two causes, the discontinuous arrangement of the
quartz rock, and the irregular protuberances, into which the surface
of the granite is formed. ‘These latter are the cause of the
semblance of alternation before noticed, both on the sides of the
right ridge, and in the bed of the Tilt. In no instance have I dis-
covered them proceeding to such a distance from the body of the
granite as to deserve the name of veins, and assuredly they are not
veins traversing the main body of granite, but on the contrary por-
tions of its solid mass. The junctions therefore of the limestone and
schist ‘with the granite, which are visible in the bed of the Tilt,
are not to be viewed as consisting in the passage of granite veins
through those rocks, a phenomenon sufficiently common in other
places, but as the points of junction, as I shall soon proceed to show,
between a great bed of stratified rocks and acentral mass of granite.
It is necessary for that purpose to enquire into the structure of the
Jeft ridge or southern side of Glen Tilt.
- Beginning from Gow’s bridge and ascending the hill at right an-

* Vide Pl. 20. fig. 3.

304 Dr. Mac Cuttocn on the Geology of Glen Tilt.

gles to the stream, a succession of limestone continuous with that at
Gow’s bridge before described is found to a considerable height in
the hill. It will be useful to point out the general bearing of this
great range of limestone. It crosses the hills at Lude, tending
towards the south, whence it passes through the Glen of Fin-
castle, and across the valley of the Tumel. Limestone is again
seen at Mount Alexander, and at the base of Schihallien, from
whence it appears to proceed through Glen Lyon to the side of
Loch Tay ; but I have not been able to trace any connection be-
tween these detached places. Eastward it extends by the side of the
Scarsough to Mar, beyond which point I am unacquainted with the
country.

To examine it more particularly. From Gow’s bridge up the
course of the Tilt to Forest Lodge it is seen skirting the banks of the
river, and alternating with schist and quartz rock, while in the places
formerly described it joins the granite, and undergoes those dis-
turbances which I need not repeat. From the river it extends up-
wards to a height of many hundred yards in the hill, although not
so exposed that we can truly ascertain what alternations it may un-
dergo through this space. Every where its course is marked by the
most lively verdure, forming a strong contrast with the brown and
barren aspect of those hills where the subsoil is granite or quartz
rock. Anthyllis vulneraria, Cistus helianthemum, Satyrium hirci-
num, and other plants which affect calcareous soils, are found on the
faces of these green hills.

This limestone is of a blueish colour, and almost always
of a large grained fracture. Where it lies in contact with
quartz rock, it is commonly of a harder texture than in more
distant portions, and where it is about to alternate with schist
it is often interfoliated with thin lamine cf micaceous or ar~

Dr. Mac Cuurocu on the Geology of Glen Tilt. 805

gillaceous slate. Although dark blue or grey is the predominant
colour, it occasionally varies through different shades to pale grey
and greenish grey, and its texture is equally liable to variations. It
is a pure carbonat of lime with the exception of the colouring in~
gredient iron, containing no notable proportion of other earths,
except where it is intermixed with the siliceous or argillaceous
laminz. The same is true of the white varieties, except that
where they are much mixed with steatite and serpentine they yield
magnesia upon being analyzed.

The dip of the beds is invariably to the south, but the quantity
of that angle is not sufficiently constant to render its measurement
an object of interest. It seems to vary from five to fifty and even to
sixty degrees. In one place and one only I| observed a considerable
contortion of the beds, and in many others there are fractures and
dislocations to be seen. Yet with such partial irregularities we may
still safely consider the general parallelism and stratification as regu-
lar, and the dip as a medium constant quantity of perhaps twenty
degrees. A few porphyry veins are found to traverse these
beds, an appearance too common to call for any particular
notice. Nor is it possible for want of marks to refer to the places
where they occur. Contortions similar to those here described
are not unfrequent in Scotland, and they have been often sup-
posed to depend on the vicinity of trap or granite. They are
however to be seen in many places where neither of these rocks can
be found, and I have observed in the island of Sky* a series of stra-
tified rocks of which the evenness and parallel horizontality is per-
fect, although they are traversed by trap veins of enormous magni-
tude and great frequency. No general conclusions therefore re-

* See the first paper in this volume.

VOL. Itt. 2Q

306 Dr. Mac.Cutrocua on the Geology of Glen Tilt.

specting a cause can be deduced from these appearances. The beds
of limestone which I have thus in a general manner described on
account of their perfect resemblance through+their whole course,
continue with scarcely any alteration as far as the burn of Glenmore,
extending upwards to a height in the hill similar to that which they
have at the western end of the ridge. The alternation of the beds
with schist and quartz rock is however more visible on the sides of
the Tilt in this part of its course; and at the river Aldianachie
in particular, there is so be seen an alternation in this order ; lime-
stone, quartz rock, limestone, schist, limestone.* The beds of
limestone do not cease at the burn of Glenmore, but after
crossing it they are less continuously visible, while at the same
time they lose the almost rectilinear course which their elevated
edges have hitherto preserved. A bed of white marble is found
among them at Fealair, and some rolled stones of pink marble in
the channel of the river point out also the probable existence of a
bed of this colour. Alternations of limestone with quartz rock and
schist continue to be seen in this southern ridge of Glen Tilt
towards Scarsough, but the pursuit being unnecessary for the pur-
poses of this paper I made no accurate record of it. It is to be re-
gretted on this account as well as many others, that no geogra-

* Rocks thus situated have by some mineralogists been divided into principal and subordi-
nate beds, but however this distinction may occasionally be found to hold good with re-
gard to some of the rocks so enumerated, yet as it is by no means a distinction universally
existing, it ought not to be erected into a general rule, since it increases the number of
artificial divisions, and offers a convenient and unmeaning phraseology instead of the lan-
guage of accurate description. Subordination implying inferiority or dependence, it should
follow that the one rock was in all cases either necessarily less in quantity, or in some way
dependent on the other. The term interstratified, involves neither obscurity nor hypo-
thesis, and is amply suflicient for the purposes of description, when combined with the
relative proportions and positions of the rocks in question.

Dr. Mac Cutzocn on the Geology of Glen Tilt. 307

phical Survey of Scotland exists on which reliance can be placed.
The errors are in fact beyond enumeration. It would otherwise
be a desirable object to trace the real line of direction taken up by
this elevated edge of limestone through the long course I have
pointed out: but it must be reserved for future examination.

Resuming now the left hand ridge of Glen Tilt at the point where
the limestone terminates, the remainder of the task of description is
easy. The whole mountain of Ben Gloe is one mass of quartz rock,
with scarcely any notable quantity of schist interstratified with it.
It is the immediate boundary therefore of the limestone bed, and
from the relative position of both, it must consequently be consi-
dered as lying above the limestone. The extent of this rock to-
wards the east is considerable, since it stretches into Mar, and cccu-
pies a great part of Glen Shee. To the west it soon disappears, or
at least its continuity is broken, since on the west side of the Garry
it is only found in alternation with schist. To the south of Ben
Gloe this rock is once more seen alternating with limestone, which
is again succeeded by the mica slate, and this without further
changes, except a gradation into clay slate, terminates at the well
known boundary of the secondary strata near Dunkeld and Blair-
gowrie.

The contortions and the conglomerate aspect of some of the beds
are the most remarkable circumstances respecting the quartz rock
of Ben Gloe; the former proving that quartz rock, like the schists _
with which it is associated, has been in a flexible state, and the latter
proving beyond doubt the partially mechanical nature of this de-
posit. Besides these it produces three coloured varieties of quartz,
pink, amber brown, and blueish grey; the former equalling in
colour the most beautiful varieties of that well known substance.

I have reserved to this place what remains to be said concerning

2 Ore

808 Dr. Mac Cuttocn on the Geology of Glen Tilt.

the rock which I have hitherto spoken of by the general name of
schist. To have described the several varieties on all occasions
where the geological history only was required, would have cre-
ated much confusion, as they rarely maintain the same character
for any considerable space. The most abundant is a clay slate,
rarely fissile, and generally of a very compact texture and dark
blackish blue colour. It sometimes possesses a glossy and unctuous
surface, and passes into a sort of talcaceous schist. It is often also
much penetrated with quartz, and on some occasions finely interla-
minated with the same substance, very beautifully banded speci-
mens of this variety occur near Gow’s bridge. On some occa-
sions it becomes intermixed with hornblende, which by degrees
predominating, the compound passes into a hornblende schist
similar to that which is so common in gneiss. This occur-
rence is frequent at the junctions, and here also the schist, even
where it is merely argillaceous, generally displays unusual hardness.
Hornblende schist is also found in beds unconnected with the clay
slate.

Micaceous schist of aspects infinitely varied is also found in this
ridge of hills. In general however it is characterized by the pre-
dominance of the quartzy ingredient, and in this way it passes
‘into quartz rock by a series of gradations which cannot be defined.
I have already had occasion to speak of those places where it as-
sumes the character of gneiss, and need not therefore repeat the
description here. I have only to add that green fibrous actinolite is
occasionally to be found in this micaceous schist, a substance which,
however radically identical with hornblende, is sufficiently distin-
guished in its appearance by characters which need not be detailed
here. In some of the rolled porphyries which are found in the
hills which bound this Glen I have observed pinite. This mineral

Dr, Mac Cuttocu on the Geology of Glen Tilt, 309

has not hitherto been found in Scotland, and as indeed it seems to
have been as yet seen in only one or two situations besides the.
place whence its name is derived, it will not be superfluous to
describe the specimens and the substance in which they are im-
bedded. The base of the porphyry is a brownish hornstone or
compact felspar, containing numerous crystals of reddish-yellow
felspar and a few grains of quartz, some of which appear to have
the primitive form of this substance. Together with these, nume-
rous crystals of pinite are imbedded in the stone, varying in diameter

from one tenth to one sixth of an inch, sometimes of similar
length, and at others mere scales. Brongniart describes it as having
been found in porphyries, and I may add that the specimens which
I procured differ in no respect from the foreign specimens with
which I have compared them.

A similar porphyry, I may here say, is to be observed in Glen
Shee. Oxide of titanium in a pulverulent or scaly and investing
form, is also to be seen in the rifts of the quartz rock in Ben
Gloe. The same disposition of this mineral occurs in Ben-na-
caillich, near Killin, and it must not be confounded with oxide
of iron, the more common metallic substance in rifted quartz.*
Among the loose stones on the skirts of Ben Gloe I also found
a singular substance. It is a laminated schist of which the basis is
clay slate, occasionally mixed with hornblende and with quartz,
and containing small lamellar and conchoidal scales of a crystalline
avhite carbonat of lime. I know not how to describe this rock
so well as by saying that the calcareous bodies are precisely like
fragments of shells, and that the whole on a first view would pass
for a shale containing shells; if found in a secondary country it

* T may here add that I have also observed rutile in quartz in the Scarsough mountain,

and accompanied by oxidulous iron in the micaceous schist of Rannoch, so that.it is net a

ware mineral in Scotland.

310 Dr. Mac Cuxtocu on the Geology of Glen Tilt.

would be thrown aside as a bad specimen of such a rock.- I would
not be understood to mean that the substances in question are
really the fragments of shells, whatever general resemblance they
may possess ; but if considered merely as crystallizations they are
sufficiently singular to be worthy of notice, since nothing analo-
gous to them occurs in the different schistose rocks which I have
examined in Scotland.

One other rock is yet deserving of notice which, although not
precisely situated in Ben Gloe itself, is found among the beds which
appertain to this great mass of quartz rock, It is visible in Glen
Fernat.

This is a mass of porphyry intermixed with a mass of quartz im
such a manner that it is impossible to ascertain precisely the rela-
tion which either of them bears to the surrounding rocks. There is
however little reason to doubt that the quartz forms a vein, but I
suspect that the porphyry also is disposed in a similar manner,
and that the appearance in question is the result of the inter-
ference of two veins. In either case the porphyry as a mineral
specimen offers an aspect I believe as new as it is difficult to explain.
Its basis is the usual indurated claystone, or compact felspar, or horn-
stone if that term be preferred, which is the most common basis
of the porphyries that occur among these strata. It contains distinct
crystals of felspar, but together with these, fragments of quartz are
also found in it. These are most obviously fragments not crystals.
They are irregular, of different sizes from that of a pea to that of an
egg, and their angles are sharp. In addition to that, where the
porphyry and quartz masses are in contact larger fragments are to
be observed mutually connected both with the porphyry and
with the quartz. Porphyry has generally been considered as a
crystallized rock, yet here it offers the mixed structure of a crystal-

Dr. Mac Cuttrocn on the Geology of Glen Tilt. 311

lized and conglomerated one. The island of Arran indeed pro-
duces some porphyry which appears to possess a structure analogous .
to this, inasmuch as grains of quartz apparently rounded, not
crystallized, are found imbedded in a common base with glassy and
earthy felspar. But that-structure might admit of dispute.

Such are the most remarkable of the independent facts which I
have noticed in this tract of country. Let us now, rejecting all
the minuter features which accompany this succession of rocks,
extend our views over a wider range, and attempt to investigate
their general bearing”. .

The most continuous bed which has occurred in this view is the
limestone. We have seen that it is regularly bedded, without
any material disturbance, with an elevation somewhat varying
and consequently in an undulating plane, and that it is con-
tinuous over a very large tract of country. We have also seen
that its elevated edge is prolonged in a line which is straight for a
great distance, and which perhaps may prove to be so even
through a greater space, when an accurate survey of Scotland shall
have been produced. It is therefore the most regular rock of the
series now under examination, and may consequently be taken as
the point of comparison for the others and as that from which the
true relations of the rocks on each side of it must be investigated.

It is indifferent to the object which I have at this moment in
view, whether the beds of limestone are considered as having been
originally deposited in their present position, or whether by subse-
quent changes they have been diverted from one more horizontal.
It will not be denied that they are deposited rocks.

If we now trace upwards from this continuous bed of limestone
we shall find that it is followed by a large and continuous bed of

* Vide Map, Plate 1.

312 Dr. Mac Cuttocu on the Geology of Glen Tilt.

quartz rock, and we have also seen that the calcareous beds them-
selves alternate with beds equally continuous of quartz rock and of
schist. We have seen that the great mass of quartz rock is followed
by a small bed of limestone, and that this again is succeeded by mi-
caceous and clay slate, terminating the series of the bedded rocks in
this direction. Here then is an order of rocks different from that
which we are taught to believe universal, since the micaceous schist
is far removed from the granite, and only follows a succession of
limestone and quartz rock. It is the limestone which immediately
follows the granite, and that granite is probably a portion of the
great mass which forms the central granite of Scotland.

This contact of the limestone and granite is-too well marked to
admit of dispute, however, like many of the other remarkable cir-
cumstances attending on Glen Tilt it has been overlooked.

But there are other important phenomena which accompany
the junction of the limestone with the granite. Recurring to the
alternations between the limestone and the beds of schist and
quartz rock with which it is continuous, we find that these alterna-
tions are regular, even, and defined. But if we now trace down-
wards to the granite, we do not find any one of these beds conti-
nuously in contact with the granite; on the contrary it is some-
times the schist, sometimes the quartz rock, sometimes the lime-
stone, or there is a want of conformity between the granite and the
rocks which lie above it. This is not the appearance which we
ought to expect had the superincumbent strata been deposited on
the previous basis of granite. If the granite had been the lowest of
a series of deposited rocks and the basis on which the incumbent
ones were precipitated or crystallized, all the strata which lie on it
should have followed upwards from it in a regular order of succes-
sion. That rock which was contiguous to the granite in one place

Dr. Mac Cuirocu on the Geology of Glen Tilt. 313

should have been contiguous to it every where, since this law is in-
variably found to hold good among rocks of which the stratification’
is demonstrated. ‘This observation is of importance, and [| have
illustrated it by two sections, the one showing the fact as it ac-
tually exists, and the other the order which should take place had
the strata been regularly deposited on the granite.* In addition to
the irregularity of this line of contact, symptoms of confusion and
disturbance are apparent,t in every instance where the granite is
actually visible in contact with the neighbouring rocks. These
consist in a general mixture of all the stratified rocks with the
granite, and a total discomposure of their regularity, being at the
same time accompanied by the passage of minute veins from the
mass of granite into the stratified rocks. Where on the contrary
the beds lie out of the immediate vicinity of the granite, they retain
their parallelism and regularity, its influence appearing to extend
to a very short distance beyond the point of actual contact.

The real structure of Glen Tilt, and the true cause of the ap-
peatances which have excited so much notice, must now be seen
so clearly to follow from the history of the rocks which bound it,
that it is almost superfluous to give a summary view of the whole.
I will however conclude this account with such a sketch, illus-
trating it by a map and such sections as may render the whole
more obvious to those who may be inclined to follow me over the
same tract.{ The map does not pretend to minute accuracy with
respect to every rock over this large space. It would have been in
fact impossible to have laid down such details on a survey of this
nature, the only one which has yet been executed of this district.

Plate 21, fig. 2°. 3, + Vide Plates 14, 15, 16, 17, 18, & 20 fig. 4.
} Vide Plates 13 & 20.
§ I am indebted for this Map to the Duke of Atholl, it being the survey of part of his
estate, and executed by Stobie, the author of the General Map of Perthshire.

VOL. ir: aR

314 Dr. Mac Cutiocu on the Geology of Glen Tilt.

But however defective and however misplaced in point of dis-
tance many of the most remarkable boundaries can scarcely fail of
being, it is sufficiently accurate in the general features for all geo-
logical purposes. The sections are necessarily general, and are
given not as actual sections of any particular points, but as illus-
trative of the relative superpositions of the rocks.

The course of the Tilt may therefore be considered as bounded
on one side by the outer edge of the granite mass of the Gram-
pians, and on the other by the primary rocks which follow and
are superimposed on it. These rocks consist of an alternation of
limestone, schist, and quartz rock.

The bed of the river is cut upon the line of contact of these two
separate classes of rock, lying upon the surface of the granite, and
against the elevated edges of the stratified rocks.

Its action has in various instances exposed the junction of the
granite with the stratified rocks, and these exposed parts are the
confused mixtures in the bed of the river which have already
been described

Although the river follows this line of junction in a general
view, it does not follow it so accurately as always to keep. the
granite on its right bank, and the stratified rocks on its left.

For this reason the stratified rocks are sometimes seen crossing to
the right bank, and even ascending high up the right side of the
hill. The granite also crosses to the left in a few cases, but as it
dips under the stratified rocks it is not found in the hill.

The Sections which are given illustrate this variation and explain
its cause. yaa rong

The apparent alternation of the granite with the stratified rocks
is also explained by attending to this arrangement.

The granite masses which extend beyond the general surface of

Dr. Mac Cuitocn on the Geology of Glen Tilt. 315

the granite, and are found in the bed of the river, do not run to any
extent through the mass of strata. It is therefore probable that
they are not veins, but simply irregularities, of the granite.

The junctions of granite in the Tilt are not therefore the transit
of independent granite veins like those of Portsoy or Rona, but the
interrupted portions of a continued line of junction between a great
surface of stratified rocks, and an equally extensive but irregular
surface of granite.

Wherever this junction is found, a complicated disturbance of
the whole rocks at the point of junction is seen, and small veins of
granite are observed penetrating the stratified rocks.

In these places of junction the granite becomes so intimately
mixed with the limestone as to alter its character, and wherever
the granite is in contact both with schist and limestone, a similar
mixture and transition between those two substances takes place.

In all other cases the schistose and calcareous rocks preserve both
their regular disposition and their ordinary chemical characters.

Z2r2

316 Dr. Mac Cuxtocu on the Geology of Glen Tilt.

I have reserved for a separate description some interesting
circumstances relating to Glen Tilt, because they are extraneous to
the general appearances, which required to be considered in one
collective point of view, and because they would have interrupted
the continuity of the narrative. The first of these is a deposition
of calcareous matter, which was pointed out to me by the Duke of
Atholl, to whose unwearied kindness and friendship I am no less
indebted for the facility which I experienced in examining this
district, than the science of geology is for this very interesting fact.
‘On the brow of the hill above Gow’s bridge a large bed of shell marle
is to be seen. It is found_on the left side of the river commencing
under a face of limestone and extending for about 250 feet or
more down the hill. It is between 80 and 90 feet wide, and its
depth seems to vary from one foot to six or more. This
appearance is unexpected but it is not solitary, as another similar
instance occurs at the foot of the limestone ridge at the south of
Ben Gloe, as well as on the hill of Tulloch formerly mentioned,
but in neither of these cases so well marked or so extensive as the
present.

The formation of shell marle in the peat mosses of Scotland is
I believe well known to the Society, as it has long been to the
agriculturists of Scotland. ‘These deposits are by no means
uncommon, whether in the larger tracts of peat, or in the smaller ones
which are found occupying insulated patches on those hollows in
the mountains which are favourable to the growth of this substance.
They are found forming beds, generally of no great thickness, but
varying from an inch or two to as many feet, and lying under the

Dr. Mac Cutrocu on the Geology of Glen Tilt. 317

covering of peat. The calcareous matter is commoniy small in pro-
portion to the clay, sand, and other foreign substances which they
contain, in so much that they are seldom of any value to the agri-
culturist. A few which I examined were found to contain from ten
to fifty per cent. of carbonat of lime; and independently of the clay
and sand which enters into their composition, they are usually black-
‘ened by a mixture of half decomposed and carbonized vegetable
matter. It is easy to perceive from the flatness of their surfaces and
their tolerably uniform thickness, that they have been formed at ‘the
bottom of water in lakes of different dimensions, which have been
gradually obliterated, partly by the influx of earth, and partly by
the growth of those well known vegetables which have covered
them with their present stratum of peat. In the instances which
I have had an opportunity of examining, the shells from which
this calcareous matter has originated have been either so thoroughly
decomposed, or from their tender structure so mutilated and
broken, that I have never been able to collect a specimen capable
of being ascertained. Other mineralogists however have examined
the shells found in these beds, which were long since known to
the late Dr. Walker, and of which an account has been given in
some of his works.

The formation in question is of a nature entirely different, and
has never yet been noticed by mineralogists: its novelty at least
renders it a matter of some interest.

Where the great limestone bed, which I have described as
occupying the southern side of Glen Tilt, is about to meet the
quartz rock, it forms a range of small abrupt faces or scarps
extending in an interrupted manner for perhaps a mile. These
may vary from ten to thirty feet in height. In wet weather small
streams fall in cascades over them in two or three distingt places ;

318 Dr. Mac Currocu on the Geology of Glen Tilt.

and generally the surface-water from above trickles down their
faces. In these parts, thus subjected to the action of water, the
limestone is dissolved and deposits here and there a white crust of
carbonat of lime resembling the usual deposits of calcareous
waters, so as to whiten in many places the surface of the rock.
One cascade of considerable height has thus left the marks of its
intricate course in the dark and broken rocks so perfectly, that
even in dry weather it appears to be always flowing, and only
a narrow inspection discovers it to be an imitation; a painted
cascade formed by the hand of Nature. I have been the more
particular in describing this fact and its extent, for the purpose
of showing that the marle bed is not produced by a deposition
of calcareous earth from the water thus impregnated. Were this
the case it should be found under the whole extent of this range
of rocks, whereas it is limited to one spot and that one a point
where the water flowing from above is diverted from it on each
hand by sinuosities in the scarped face. I do not assert that
there is absolutely no other deposition of a similar nature in any
other place throughout the great extent of the limestone range
of Glen Tilt, but after a considerable search I did not find any in
those neighbouring parts where the surfaces of the rock were
whitened, and the greater flow of water would have led me to
expect it, had it been a mere deposit from water. There is little
doubt that a portion of the lime contained in the bed has been pro-
duced in this way, but that portion must necessarily be small, or the
same earth would be easily discovered in the soil of the immediate
vicinity which lies in similar situations, which has nevertheless
only the ordinary aspect of the whole mass of soil incumbent on
the limestone. On examining the nature of this deposit it is found
to consist of a substance much more spungy and loose than chalk,

Dr. Mac CuLtocu on the Geology of Glen Tilt. 319

although on a first glance strongly resembling its more friable
varieties. It is soluble without residuum in muriatic acid. On a
narrow inspection it is found to contain minute fragments of shells,
particularly towards the surface, while deeper in the bed all marks
of organization disappear. It is also every where penetrated by the
fibrous roots of grasses and other plants, or by the minute channels
which their decay has left. It does not acquire any induration on
drying, as the specimens before the Society will show. On the
immediate surface, or at small depths where the decomposing causes
have had less time to act, entire shells are found, and numbers of
these may be collected in a very perfect state. Among those which,
I did collect I only found the following in a state sufficiently entire
for examination.

No. 1. Helix arbustorum.

2. Appears to be Helix rufescens, or hispida.

3. Two broken specimens, of which I cannot speak with
the least decision.

4, I conjecture it to be Helix fusca of Montagu ; and perhaps
it agrees with Draparnaud’s genus Vitrine. By

5. A small Planorbis; but of what species I am unable to
determine. }

G. Appears to be a minute Lymneus; perhaps Lymneus
minutus of Braard.

All: appear. to be terrestrial shells.

This then is to be considered as a land formation of calcareous
matter, if we may use such a term, and the result of the successive
renewal and death of these minute animals for a length of time
unknown. Whether, this process, is, still going on I was unable
to discover, After much search I did not find any living animal,
but among the helices were some with their colours so perfect,

320 Dr. Mac Cuttocn on the Geology of Glen Tilt.

that their death could not in all probability have long taken place.
As the animals themselves are known to be existing species, it is
indeed probable that this bed is still in a state of increase, however
tedious and imperceptible the process may be.

Here then we have a fact which presents us with another
modification of those strata which owe their origin to the action
of living animals, or to the accumulation of their remains. It
has always been known that marine animals acted an essential
part in the production of the secondary, and even the latest of the
primary, (or ¢ramsition,) strata. It has lately been shown that
considerabie deposits and large beds of rock have also in former
times been produced by testacea inhabiting fresh waters. But
it has never been suspected that similar deposits could be formed
on dry land. That such is the case here, is sufficiently evident
from the angle of acclivity on which this bed is formed, on a
surface which has assuredly undergone no alteration of its position
since its formation, or at least since the formation of the granite.
The fact itself is much too insulated and too narrow to admit of
‘any generalization, or to justify us in supposing that similar for-
mations might have taken place in a more ancient state of the
globe. Else speculative minds might conceive that of the nume-
rous elevated and apparently displaced strata which are now found
containing organic remains, of which, not only the species, but the
very genera as well as habits are unknown, some at least might
have been derived from land animals, whose remains were converted
into rocks in the very places where they now exist. Should causes
ywith which we seem but very imperfectly acquainted at present,
hereafter convert the marle bed now described into a rock, and all
traces of its recent formation disappear, a circumstance at least
within the limit of possibility, assuredly future geologists would

Dr. Mac Cuxrocn on the Geology of Glen Tilt. 321

not be.a little puzzled to reconcile its appearance with that of the
surrounding rocks, of which the intricacies already described in
this paper, are sufficient in themselves without the further addition
of such a deception as this.

It were to be wished that this specimen could be preserved for
the future examination of others, but the wants of agriculture must
be satisfied, and the pick-axe and spade have already commenced
their depredations.

~The next appearances in Glen Tilt which I consider worthy of
notice, and which are extraneous to the general structure already
described, are the marks which it bears of the action of water.
If we consider the general characters of the rocks which form the
Opposite sides of the valley, and attend to the section which
accompanies the description, it will be seen that the channel of
the river during the greater part of its course, is cut upon the
junction of the stratified and the unstratified rocks ; in consequence
of which those junctions which form so material a part of the interest
of this valley have been exposed. It is easy to conceive that a longer:
continuance of the same action may expose a greater portion of
this line, and ultimately lay bare the granite which doubtless lies
below the stratified rocks beyond Glen Criny or Gow’s bridge
down the course of the Tilt. If from future probabilities we ascend
to past ones, we may imagine the river once flowing at a higher
elevation, and gradually making its way on the surface of the
granite and against the edges of the soft strata; the former offering
a constant resistance, while the latter, giving way to its action,
have formed those precipitous faces the displaced fragments of
which have during the progress of time been rolled along the
valley to the course of the Garry; being destined in their ultimate
progress to assist in forming the immense beds of alluvium which

VoL. II. Zs

322 Dr. Mac CuLtLocnu on the Geology of Glen Tilt.

mark the course of the Tumel and the Tay, and to exclude the
sea which once fiowed high up into the present estuary of the
latter river. od

The actual corrosion produced by the mountain torrents is most
strongly marked in those which fall from the skirts of Ben Gloe to
join the Tilt. It is easy to perceive in these, that the fortuitous
inclination of the strata has not produced the intervals now occupied
by the streams, but that beds once continuous have been cut
through often at right angles to their direction, leaving their
sections fairly exposed in the deep beds of these powerful agents.
The depth of these sections is always striking and frequently
enormous, exceeding an hundred feet; with sides almost perpendi-
cular, while the dark and turbulent water roars, seldom visible, and
scarcely audible, beneath. In the progress of waste and ruin the
falling of the upper parts gradually produces a more open chasm,
destined perhaps in the progress of time to form a glen such as
those narrow and prolonged ones which constitute a frequent
feature throughout this district.

To what extent these agents actually operate in changing the
present surface of the globe, is an enquiry beyond the objects of
this brief notice, but we have, in this valley as in numerous other
parts of this country, abundant proof, that many of the most
conspicuous and extensive alluvial deposits have had their rise in
causes of a much more general and extensive nature.

Of this a very remarkable example is to be seen near the farm of
Auchgowall in the lower part of the valley, extending to Gilbert’s
bridge. It is most conspicuous on the left bank, where it is seen
covering all the hills to a considerable height and a great depth, its
thickness being distinctly shown by the sections of the streams
which descend to join the Tilt, and of which the courses are

Dir. Mac Cutxocu on the Geology of Glen Tilt. 323

marked by extensive ruin: the bare schistose foundation has also
been in many places exposed. The alluvium in question consists
of the materials of the surrounding country, but all of them
water worn and mixed with sand and gravel as from considerable
attrition. In this, as in numerous other examples, there is no
assignable mode in which the materials could have been either
formed, or deposited, by the slow action of the existing streams,
while the total absence of a similar deposit in other parts of the
valley equally subjected to similar causes, bespeak a different
origin. ‘The cause appears to have been of a diluvian nature, and
the determination of the deposit to this point, may perhaps be
found in the form of the valley at this place and the obstruction
which it has offered to a mass of matter impelled through the
upper parts where no such obstruction to its deposition existed.
Such an obstruction as that which I have suggested might formerly
perhaps have been rendered more complete by the continuity of
the strata beyond this point, which has since been gradually destroyed
by the slow action of the Tilt: in consequence of this the deposit of
alluvial matter has itself gradually diminished, sliding successively
down the hill as it has been undermined, and together with the
more gradual abrasions of the land in the upper parts of the valley,
hurried by the daily course of the river to the Garry.

The probability of this supposition is strengthened by the occur-
rence of a similar circumstance at no great distance. This may be
seen near the junction of the Garry and the Tumel in the hills
above Fascally ; and the deposit is here also of enormous thickness
and of similar materials. Like that in Glen Tilt, it occurs where
the valley appears to have favoured the accumulation of a diluvian
deposit, and where the subsequent action of the river in its rapid
and corroding progress downwards as it runs through the narrow

Zs 2

324 Dr. MAc Cutocu on the Geology of Glen Tilt.

openings at Killicrankie, has hitherto proved insufficient to under-
mine and remove it; in consequence as it would seem of the lateral
direction of its course produced by the fall of those portions of
alluvium which have formed the small holm on which Fascally is
situated. Thus it is for the present protected from change, and
perhaps destined to remain, for a longer period than that in Glen
Tilt, a monument of those revolutions which point out an extensive
but transitory action of water on the surface of our globe.

I have remarked in the preceding paper, that the granite which
forms the right boundary of Glen Tilt has the property of affecting
the magnetic needle. This influence is far from inconsiderable,
and in many cases produces not only remarkable local variations,
but a disturbance of that instrument so great as to render it useless
for the purposes of ascertaining any meridian whatever. It is not
limited to the syenitic varieties, where from the predominance of
hornblende we might reasonably expect to find it more active, but is
equally to be found existing in those granites which do not contain
this ingredient. Neither does it depend apparently on the micaceous
ingredient, since in many of the rocks which shew it strongly the
mica is in very small proportion, It seems to be equally independent
of a state of decomposition in the granite, since it is here, as elsewhere,
to be found inherent in fresh specimens, although on the summit of
Goatfell in Arran, as I have remarked on a former occasion, it
appears most conspicuously in those specimens where the iron is
becoming carbonated and the rock is tending to disintegration. In
the paper to which [ here allude,* I noticed this fact as being nearly
a solitary one at that time, but I have had occasion to observe it
since on various occasions. In a paper on Cruachan, drawn up

* Geological Transactions, vol. ile

Dr. Mac Cutrocn on the Geology of Glen Tilt. 325

three years ago, the same circumstance is described, and I may
here repeat that the granite in question is not decomposed, and
contains a very large proportion of flesh coloured felspar, the
quartz and mica being in small quantities. As granite is a rare
rock in Scotland, I have not been.able to extend my observations
on this substance far, but I have also found the same magnetic
power in some of the granites which form the Ross cf Mull.
The porphyries also occasionally possess the same power. I have
observed it in different places, but most remarkably in those of
Cruachan, and expect that it will be found most conspicuous in
those, which from their black colour contain much hornblende
and approach to trap in their composition: it is not always that
circumstances allow of the repetition of these observations. I
have not often discovered it among the primary schists, but I
must add at the same time that my trials on those rocks have
been but few. Yet it occurs among the schists in the hills which
border Glen Tilt in more situations than one, although seldom in
an energetic degree. It is not limited to the hornblende slate, but
is found in those specimens of argillaceous schist into which that
mineral does not enter. I have also observed that some of the
beds of dark blue limestone exert a disturbing force on the
needle, and imagine that I found it greatest in a stratum which
crosses the upper. part of Glen Fernat at the foot of Cairn Ree.
I have however examined limestones of the same apparent nature
in other parts of Scotland without having discovered a similar
property in them, so that I conclude it will be found but rarely
either among the rocks of this family, or the schistose ones.

It has so long been known and so often remarked as a quality
common to the rocks of the trap family, that instances of it must
have occurred to every geologist. In these indeed it is often so

326 Dr. Mac Cutrocg on the Geology of Glen Tilt.

conspicuous as to have become an object of popular curiosity,
notwithstanding which, it has rarely attracted the attention of |
geologists, unless, as in cases like those here alluded to, it has been
exerted in an uncommon degree. I may therefore add that it is
very generally diffused among the rocks of this family, although as.
we might reasonably expect, in very different degrees, those
variations of energy depending at times on the peculiar composition
of the rock, at times on its state of decomposition, and at others on
circumstances which we have not the means of ascertaining, little
acquainted as we are with the laws which regulate the movements,
the accumulation, or the permanence, of this mysterious power.
In a paper on Canna,* which I presented to-the Society some
years ago, I pointed out the great action exerted by the trap in
several parts of this island, as well as in that spot so well known to
the inhabitants and to mariners by the name of Compass-hill, and
took occasion at the same time to recommend to surveyors who
are in the practice of using the magnetic needle in their art, the
necessity of attending to these disturbances hitherto held of no
moment, or rather, I might say, unknown and unattended to by
them. I also pointed out with similar views the same effects
occurring in several parts of the island of Sky, where they are
frequent and powerful. Among the places in that island where
the needle undergoes violent disturbances the hill of Glamich is the
most remarkable, but as in that papert I have entered into the
details which respect this spot, I need not repeat them here.
{ must however add that this hill consists partly of clinkstone,

together with the porphyries which are usually associated with it,

* This paper does not appear, having been retained for the purpose of connecting it
with the history of the neighbouring and similar islands.

+ Printed in this volume.

Dr. Mac Cuitocn on the Geology of Glen Tilt. 327

and partly of that syenite which appears to belong to the same
family, being, like the clinkstone, superimposed on the secondary
strata. Here the blue clinkstone possesses the magnetic virtue
in the most eminent degree, but it is also attached to the syenite,
as well as to the grey porphyries which are derived from it by the
same imperceptible gradation as are the porphyritic varieties of
clinkstone from the simple ones. | .

The magnetic property of a rock of serpentine was remarked by
Humboldt some time ago, and I have also found it in this rock in
the only situations where I have as yet had an opportunity of ex-
amining it, namely at Portsoy, and in the island of Scalpa.* In
both these places the magnetic power is considerable, and in some
particular spots nearly as great as in the most striking examples
among the trap rocks. In hand specimens I have also found that
the serpentine of Anglesea, and that known by the name of Egyptian
green, exert considerable influence on the needle, so that the
property is in all probability generally dispersed among the rocks
of this description, as it is among the traps. I may add finally,
that I have observed it, but sparingly and feebly, among some of
the dark pitchstones, and that in the augite rock which I have
formerly described as forming so large a part of the island of Rum;
it is as vigorous and common as among the traps with which that
rock has so strong an affinity both in mineralogical and geological
character.

Such then is the catalogue of the rocks among which I have
found the property of disturbing the magnetic needle by the exer-
tion of their own magnetic powers, and it will be seen that they
occupy a considerable share of those rocks which constitute the

* To distinguish this Scalpa from other islands of the same name, I must say that it lies
at the eastern side of Harris, and is remarkable for its lighthouse.

328 Dr. Mac Cuttocu on the Geology of Glen Tilt.

surface of the earth. Geologists, hereafter perhaps more attentive
to this subject, may probably add to this catalogue, or at least aug-
ment the number of examples, and add many more to the few lo-
calities. which I have had opportunities of examining.

To surveyors who are more deeply interested in the fact and its
consequences, I shall also look for more extensive and more accu-
rate observations, since the possession of more delicate instruments,
and the devotion of time and attention to this particular object, are
required to determine the quantity and extent of these influences, as
well as their practical effect in producing permanent local variations
in the magnetic meridian.

I need scarcely say that an ordinary ships compass is insufficient to
detect these variations, unless where they are considerable, as the
instrument, either from the rudeness of its workmanship, or the
intentional insensibility given it by the maker to render it steady in
steering small ships or in navigating through a cross sea, is rarely’
alive to minute quantities of the disturbing force.

I have attempted on various occasions to discover the positions
of the poles of the natural magnets which thus disturb the needle
brought within the sphere of their influence. From the observation
of Humboldt we are led to imagine that he conceived the. rock or
mountain which he describes, to have possesed but two poles, and
that its effects on the needle could in consequence be easily as-
signed. ‘This is not impossible, but in-all the cases where I have
been able to make observations, I have found that the disturbances
must have been produced by a number of independent magnets,
each rock or fragment being possessed of a meridian of its own,
and the disturbances of the needle being in consequence of
that, extremely irregular and uncertain. I have already entered
into a detail of this fact where I first observed it in Sky, in the

Dr. Mac Curtocn on the Geology of Glen Tilt. 329

paper to which I have already alluded, and shall not therefore re-
peat it here. On the extent of their influences I have also spoken
in the same place, where I have shown that the needle was sen-
sibly disturbed even at the distance of four feet from the ground.
There can be no doubt that influences of this power and extent
will produce local variations which if not absolutely permanent,
will, by affecting the other better known variations of the needle,
introduce errors into those observations which assume for granted
a certain local and temporary variation on the evidence of obser-
vations made at a distance from the precise point where these addi-
tional disturbing forces are in action. |

It.is already well. known to philosophers that the ordinary varia-
tions of the needle are not steady, either through small spaces of time,
or over a considerable extent of surface, and it is well known that
in different parts of Scotland the quantities of the variation are sub-
ject at any given time to considerable differences. To this cause
are doubtless to be attributed errors in geodesic operations which
have occurred even to experienced observers, where these differ-
ences were either neglected or perhaps not suspected.. The errors
in General Roy’s Survey of Scotland, appear to have been derived
at least in part from this cause. It would be interesting to know
how far these local differences depend on the magnetic influences of
masses of rock, or merely on the same mysterious cause which
produces the ordinary variation, acting in an unequal manner,
We must look to future investigations for the solution of this
question. In the mean time, while we are sure that such
irregularities actually exist, it is plain that much caution is
required in the use of surveying instruments, where magnets
are concerned either in the observations, or in the adjustment.

Vou. It. 2T

330 Dr. Mac Cuttocu on the Geology of Glen Tilt.

In the ordinary operation of maritime surveying by the needle and
sights, the errors are often likely to be considerable ; more particu-
larly where some of the angles are determined with the instrument
placed on shore, mariners having been uninformed with respect to the
existence of such disturbing forces. To such causes it is very pro-
ble are owing the discrepancies found in charts of new or distant
coasts, where the instruments have even been good and the obser-
ver practically expert in its use. It is even probable that the charts
of the west coast of Scotland, constructed by Mackenzie with
abundant leisure and experience in his art, owe many of their very
glaring errors to this cause, which on many of these coasts is
exceedingly active. Want of care or want of accuracy, as far as this
could be obtained by the means which he possessed, cannot be im-
puted to him, as the soundings, distances, and enumeration of
even the most minute sunk rocks, is surprisingly accurate, render-
ing his work such, that even the most inexperienced pilot may enter
these intricate harbours and come to his anchorages with no other
guide, as I have abundantly verified on numerous occasions. If, as
has been said, the well known map of North Wales constructed by
Evans, was also surveyed by the compass, we may perhaps attribute
a portion of the errors which it comprises to this neglected cause
among others. It is true that the repeated comparison of bearings
will afford some correction to inaccuracies of this nature, but a me-
dium of bad observations can never produce a good one.

At any rate where such an instrument is to be used it will always
be prudent to erect it on a staff at some distance from the ground,
as we shall then at least avoid those disturbances which result
from the contact, or very near approach of rocks when it is
placed on or near the ground. This addition is easy and of
little incumbrance to the operator, and as the compass and

Dr. Mac Cuttocu on the Geology of Glen Tilt. 331

sights is so useful and convenient for ordinary purposes, it will
at least render it one degree more correct, although even in this
way we shall not avoid those disturbances which arise from -the
more extensive influence of larger masses of magnetic matter. This
caution is equally necessary to the geologist in the taking of geo-
logical bearings or angles, since the errors which may arise from
its position on the ground are generally considerable, on account of
the delicacy of the needle of a pocket compass, and may often be as
great or greater than those which proceed from the short. radius of
the instrument itself, and the consequent difficulty of accurate
observation.

In the use of the miner’s compass the species of error which I have
here noticed is always in danger of becoming serious, from the
difficulty of removing the instrument to a sufficient distance: from
the disturbing forces. Yet even in the narrowest shaft or level an
attention to this will enable the miner to take precautions, which,
if they cannot entirely remove, will at least diminish in a great de-
gree the probability of serious error.

In adjusting the position of acommon theodolite it is ee that
one of the sources of error will be sometimes removed, and always
diminished, as it rarely happens that the local influences of small
masses are felt at the distance at which that instrument is elevated
from the ground. Yet I have shewn in the instance of Glamich,
that the disturbing power was sensible at four feet from the sur-
face. Such cases are however rare, although the ordinary quantity
of the variation will be altered at distances infinitely greater, where
the action of mountains or large tracts of magnetic matter is con-
cerned.

In general I may remark that no confidence can be reposed in
magnetic angles until the regular action of the needle has been as-

i OE.

332 Dr. Mac Cuttocn on the Geology of Glen Tilt.

certained by repeated observations on its steadiness at different ele-
vations above the surface, and at different points upon it. It is not
a sufficient trial that detached specimens of the rocks in the vicinity
exert no action on it, since the variations will often be sensible from
the joint action of a considerable mass of polar matter, when small
pieces of the same substance produce no effect. The dipping needle
would give the most correct information respecting the existence of
these local causes of error, but it is an instrument unfortunately
too nice and expensive for ordinary purposes. In all cases where
such a disturbing force is suspected to be in existence, and where
accuracy is necessary, we should not be content until the ground has
been examined and the actual variation ascertained by the observa-
tion of the magnetic azimuth, wherever it is practicable to procure
such an observation. It would however tend still more to the re-
moval of all possible errors arising from this cause, if surveyors
were to reject the use of the needle altogether, and depend solely on
the back angle; since although every one who lays claim to accu-
tacy will correct the one observation by ,the other, yet the temp-
tation arising from the facility of using the needle alone, is perhaps
too great to be always resisted.*

After this paper had been prepared for the Society, the voyage of Captain Flinders
was published. It gives me great pleasure to find so thoreugh a confirmation of my ob-
servations and suspicions on this subject, in the original remarks of that indefatigable
and unfortunate navigator. I was also pleased. to see that he had frequently
observed the polarity of granite; more frequently I doubt not than it has occurred
to me, had he published the details of all his observations. There seems to me
also some reason to think, from a remark on which however he does not lay much
stress, that he imagined that property to be more conspicuous on the summits of hills
than clsewhere.

Dr. Mac Cuxntocn on the Geology of Glen Tilt. 333

StncE this paper was prepared for the press, there has been
published in the Transactions of the Royal Society of Edinburgh a
description of the same place, drawn up from the joint observa-
tions of Lord Webb Seymour and Professor Playfair. Among
other differences, such as may be expected to occur in the obser-
vations of different individuals, and which are not subjects for dis-
cussion, there are some which call for remark, since they involve
questions of nomenclature, the discussion of which may be useful
in the present uncertain state of that important preliminary to geo-
logical observation. It is much to be desired that all observers
should agree in the denomination of those rocks respecting which
frequent discordances arise, since without such agreement there
can be no prospect of a definite application of terms.

Gneiss is described in that paper as of frequent occurrence.
With a few trifling exceptions the most remarkable one of
which I have described, I have no where observed any real gneiss
among the schistose rocks which form the left ridge of the
valley or the great mass of stratified matter. These schistose
rocks, as far as my observations go, are clay slate, mica slate,
hornblende slate, and quartz rock. Gneiss is a rare rock in Scot-
land, and is principally to be found in the Long island, in Tirey,
Coll, Rona, Iona, and Isla; as well as on the mainland, in Glen
Elg, and Morven. I do not consider the rock which is of such
frequent occurrence between Blair and Loch Spey, already des-
cribed in this paper, as gneiss, since although the form is laminar
the structure is not foliated: nor have I observed that the gneiss
of Scotland any where alternates with mica slate, although it does

334 Dr. Mac Cuttocu on the Geology of Glen Tilt.

with clay slate, nor that it has any immediate connection with
granite, much as it resembles it in’composition. But in mica
slate, as well as in the micaceous quartz rock which occurs
in the vicinity of granite, a real gneiss is not unfrequently seen
near the points of junction; the schistose rock which in other
parts consists of quartz and mica in various proportions, having
felspar superadded, and preserving the same parallelism in the
disposition of the mica which it possessed before the addition
of that ingredient. This change is of various extent, in some
cases not reaching many inches beyond the line of contact with
the granite, and gradually disappearing even in the lateral pro-
gress of the laminz, while in other instances it occupies a more
considerable space. But in no case that I have witnessed is it
prolonged through the whole extent of a bed so as to allow us to
say that beds of gneiss alternate with or precede the mica slate.
I conceive the appearance of gneiss which I have described in
Glen Tilt to be of this partial nature, and in all probability owing
to similar causes. I would also remark that as quartz rock is
evidently recomposed from the ruins of ancient granites, it often
contains all the ingredients of that substance. In the extensive
remarks which I have made on this rock, as yet so little ob-
cerved, I have noticed instances in which it has been mistaken for
granite. In the same way it may be mistaken for gneiss, since
with a stratified structure it may contain all the ingredients of
that substance. Nay, even the mica may be disposed in the same
parallel form in the triple compound as it is in the more ordinary
mixtures of quartz and mica. Even here however an experienced
eye may detect differences which words are inadequate to de-
fine, and the true connections and nature of the rock may be
known, by tracing its connections with, and gradation into, the

Dr. Mac Cutrocn on the Geology of Glen Tilt. 335

more characteristic beds of quartz rock with which it is as-
sociated.

The next remark I shall make is on the term syenite, which in
the paper alluded to is applied to that rock which I have called
granite. The difference here is merely a question of expediency,
and I shall content myself, in addition to what I have already said
on that subject, with a brief statement of my reasons, as I shall
have occasion to discuss this point at some length in giving an ac-
count of the Western islands.

Werner has described syenite as an overlying formation, and
incumbent on granite. With a rock of these characters I have no
acquaintance, and his description is therefore unintelligible to me
in a practical view. '

But there are in Scotland (and elsewhere) two compound rocks
formed of the ingredients described in his definition, namely,
quartz, felspar, and hornblende, but occupying two positions, in a
geological view most distinct, and neither of them agreeing with
that which he has assigned for his syenite. That to which
I have thought it expedient to limit the term, is incumbent upon
the secondary strata and at the same time interferes. with them in
the same way that certain varieties of trap and porphyry, with
which it is intimately connected, are known to do ; examples of this
are to be found in many of the Western islands. It is therefore
not only posterior to these strata and distinct from the syenite of
Werner in its geological relations, but it differs from it in compo-
sition, inasmuch as it does not contain mica, unless, as some also
of the traps do, accidentally.

The other rock which agrees with the mineralogical definition of
syenite, is found connected with granite and consequently subja-
cent to the most ancient stratified rocks, I have attempted to shew

336 Dr. Mac Cuttocu on the Geology of Glen Tilt.

in this paper, that it passes into granite, and is associated with
it in an intimate manner, having no further the appearance of stra~
tification or of an overlying character than granite has, and bear-
ing precisely the same relation to the stratified rocks which that.
does. In aspect it has generally a considerable resemblance to granite 3
often indeed it cannot be distinguished without a careful inspection,
while the syenite which lies above the secondary rocks rarely has
a granitic aspect. This variety frequently contains mica as well as
hornblende, and it is indeed not rare to find the former ingredient
far exceeding the latter. ‘There appears therefore a sufficient mi-
neralogical distinction between these two rocks to justify us in dis-
tinguishing them by two names, without infringing the rule which
I have suggested on another occasion,* that we were not at liberty to
vary our principles of nomenclature, by drawing them sometimes
from mineralogical character, and sometimes from geological po-
sition. But for this purpose it is necessary that the whole of any
mass of rock should be considered together, and that its mineralo-
gical character should be defined by its prevailing, not by its oc-
casional composition. Whatever more experienced geologists may
determine on this question, it is indubitably necessary that the con-
fusion, which I have here pointed out should be removed by some
expedient, and I shall gladly conform to any better suggestion; but
it is too plain that the indiscriminate application of the term syenite
to two rocks so essentially different in connections, would tend to
produce a most incurable confusion in geological description.

The last remark which I shall make on the apparent discrepancy
between my observations and those of the philosophers above-
mentioned, is also little else than a question of nomenclature. It

* Vide Miscellaneous Paper, Vol. II. of Geological Transactions.

Dr. Mac Cuitocn on the Geology of Glen Tilt. 337

consists in the use of the term greenstone, which has been applied
by them to some of the dark varieties of the syenitic granite. It
has appeared to me, as I have remarked in the body of the paper,
that these varieties of syenitic granite were distinguishable from
true greenstone by the presence of quartz, and that however mi-
nute their texture, and apparently uniform the whice ingredient, it
always contained that mineral in conspicuous proportion, while in
greenstone, a common member of the trap family, it was rarely
present, and might, when present, be considered as accidental. If
I have been mistaken in this observation, I shall consider it un-
fortunate that no criterion of a mineralogical nature can be found
to distinguish these rocks, if indeed the presence of the occasional
minerals, mica, epidote, or sphene, minerals in general of a more

ancient origin, cannot lend us some assistance. It is so necessary

to prevent rocks distinct in their geological relations from being
confounded, that the terms which are assigned to them ought if
possible to be equally distinct, since the mere effect of terms, as we

all experience, has in every science a powerful effect in mis-

leading or influencing our judgments. If there really be no such

distinction as I have here thought probable between certain syenitic

granites and the greenstones of the trap family, it will then be ne-
cessary to have recourse to the same expedient as we use in dis-
tinguishing the limestones, the addition of the terms, primary,
and secondary ; an expedient however, which in this case it would
be desirable to avoid, since many geologists are inclined already to.
distinguish by the addition of these very terms the real trap rocks
which are found connected with primary or with secondary strata,

to
S

WOL. Til.

IX. Sketch of the Geology of the South-Western Part of Somersetshire.
By LEONARD HORNER, Ese. F.r.s.

MEMBER OF THE GEOLOGICAL SOCIETY.

~

[Read March 3, 1815.]

§ 1. I BEG leave to offer to the Society an account of some ob-
servations on the mineralogy of that part of Somersetshire which
lies on the Bristol Channel westward ofthe river Parret. The short-
ness of my stay in the country prevented me from conducting my
examination with that minuteness of detail which an accurate
survey should possess, but I trust that with the assistance of the ac-
companying map* and the series of specimens which I have deposited
in the museum of the Society, the following notes will be sufficiently
distinct to afford a general view of the geological structure of that part
of England. Ihave distinguished in the map, by means of differeat
colours, the situation which the several rocks occupy, and although,
from unavoidable sources of error, the boundaries of each can
only be considered as approximations to the truth, yet I do not
conceive that the inaccuracy in that respect is so great as to affect
any geological deductions.

§ 2. Inthe western part of Somersetshire, and partly within
the adjoining county of Devon, there is a large district of high
land, the greater part wild and uncultivated, extending about 30

miles from east to west, and about 16 miles between north and
* Pl. 23.

South-Western Part of Somersetshire, 339

south, the highest and wildest part being known by the name of
Exmoor Forest. In appearance and structure it is very analogous.
to a great part of Devonshire and Cornwall, and may be considered
as the termination of those schistose rocks which prevail so much in
these counties. It is divided into several ranges of hills, distin-
guished, by. particular names, the most conspicuous of which are
Dunkery beacon, Brendon hill, Croydon hill, Grabbist hill,
North hill, and the Quantock hills. The longitudinal direction of
these is, with the exception of the Quantock hills, nearly east and.
west ; there are numerous lateral branches from each central ridge,
forming small steep vallies, or gullies, which terminate in the
great vallies that divide, and are parallel to the principal ranges.
These gullies, called Combes in the country, when richly wooded,
form some of the most striking features, of the beautiful scenery
for which this coast is so celebrated. The Quantock hills, although
cut off from the main body of this mountainous tract by a wide cul-
tivated valley, may, in a geological point of view, be considered as:
strictly belonging to it, for the range itself and the intervening
valley are formed of the same rocks as the country to the westward.
This apparent insulation, and the peculiar beauty of the range, mark
them as a prominent feature in the country; they are no less re-
markable from the varied scenery they afford, and the magnificent
prospect that is seen from their summit. The name is generally
applied in the country, as it is in the Ordnance map, to a range
of about eight miles in extent from north-west to south-east, and.
which is.in fact the highest and most conspicuous part. From the
south eastern extremity, the mass is divided into several distinct
ridges, all composed of the same materials as the Quantock hills
strictly so called, and which spread out in the form of a fan, having
one extremity at North Petherton, and the other at West Monckton,
Zu 2

340 Mr. Horner on the Geology of the

with a gradual fall to the alluvial land on the banks of the rivers
Parret and Tone. On the western side of the Quantock hills the
descent is very rapid into the valley ; on the eastern side it is in ge-
neral much less so, and a great many lateral branches stretch out
at right angles to the range, shooting off, however, considerably
below the summit. These sometimes terminate at a very short dis-
tance from the central ridge with an abrupt slope, at other times
they descend very gradually almost to the Parret, shewing occasion-
ally at their termination their identity in composition with the
central mass.

The whole of the mountainous country I have mentioned has a
smooth undulating and rounded outline, no where rugged or pre-
senting any cliffs or precipitous faces, except on the sea shore,
where sections have been formed probably by the action of the
tides. The whole country is so covered by vegetation, either in
the form of heath and turf on the high land, or of the more luxu-
riant productions of the vallies, that very few opportunities occur in
the interior of ascertaining the nature of the rock on which the soil
rests; but the cliffs on the sea shore afford such an ample field for
studying the mineralogical structure of the country, that the scat-
tered observations in quarries, may be more strongly relied on and
more easily connected.

§ 3. From the Parret to Barnstaple Bay there is no river of any
magnitude : the great watershed is to the south, and the Ex, one of the
most considerable of those rivers which fall into the English Channel,
rises in Exmoor Forest. The southern shore of this part of the Bristol
Channel is very steep, the sea in many parts not leaving the cliffs
in the lowest tides. From Minehead Point westward, the charts
give 8, 9, and 10 fathoms water close in with the shore. East-
ward of that point the coast is more flat, and towards the mouth of

South-Western Part of Somersetshire. 341

the Parret the distance between high and low water mark is in some
places above two miles. From the town of Minehead there is a
tract of low marsh land, extending eastward about four miles along
the coast, and about a mile in breadth in most places from the sea
to the base of the hills. Were it not for a bank of pebbles which the
sea has thrown up on the beach, this land would be overflowed every
tide ; and this even now generally occurs when the tides are unusually
high. A similar tract of marsh land occurs in Porlock Bay, which
is equally protected by a very great shingle bank, divided into three
terraces rising the one above the other, the highest part of the
bank being not less than forty feet above low water mark. The
pebbles, which all along the shore are of the same materials as the
cliffs in the open part of Porlock Bay, are of various sizes, but
they are in general flattened spheroids of about six inches in di-
ameter ; as they approach the cliffs at Hurstone Point, they become
gradually less, and close to the cliffs, they are of the shape and size of
a pigeon’s egg, and nearly all alike.

Dunkery beacon is stated in the report of the Ordnance Tri-
gonometrical Survey to be 1668 feet above the level of the sea,
and, with the exception of Cawsand beacon, in the northern part
of Dartmoor Forest, which is stated in the same report to be 1792
feet, is I believe, the highest land in the West of England.

Grabbist hill I found, by barometrical measurement, to be 906
feet above low water mark. The highest part of the ridge is
immediately above the village of Wotton Courtney. I made use of
Sir Henry Englefield’s mountain barometer, and I have calculated
the heights by the formula he gives.

North hill above Bratton, which appeared to me the highest
part of that ridge, I found to be 824 feet above low water mark,

342 Mr. Horner on the Geology of the

The western extremity, which I did not measure, judging from its
appearance ata distance, can be very little less than this height.

The Quantock hills when viewed from a distance, present
a gently undulating outline, which rises in three places into a more
prominent elevation, the most northern being called Doucebury,*
the central height Will’s Neck, and the most southern Cothelstone
Lodge, from which last point the range diverges, as has been al-
ready noticed. Will’s Neck is the highest of the three, and was
measured at the time of the Trigonometrical Survey, and found
to be 1270 feet above low water. It is called in the Survey the
Bagborough station, being immediately above the village of that
name. Doucebury I found by the barometer to be 1022 feet, and
Cothelstone Lodge 1060 feet above low water mark; but as both
these measurements were made under very unfavourable circum-
stances, they are not to be relied on. Doucebury must be consi-
derably higher than I found it to be; the measurement of Cothel.
stone Lodge is probably not very far from the truth, judging in
both cases from the comparison between the three heights when
seen at a distance.

§ 4. The whole of the mountainous part of this district is
formed of a series of rocks differing very considerably in mineralo-
gical characters, but which the repeated alternations of the several
varieties, and the insensible gradations that may frequently be
traced of one into another connect into. one common formation. A
great proportion of these have the structure of sandstones, the
component parts varying in size from that of mustard seed to such
a degree of fineness, that the particles can with difficulty be dis-
cerned. Quartz and clay are the essential component parts of all
the varieties, but in different proportions. The quartz in some

* This is the name by which it is universally known in the country, but it is called
Danesborough in the Ordnance map.

South-Western Part of Somersetshire. 343

instances prevails to the entire exclusion of any other ingredient,
forming a granular quartz rock: it is more abundant in the aggre-
gatés of a coarse grain, clay being the chief ingredient in those of a
close and fissile texture. They have all an internal stratified struc-
ture, which is less apparent in those of a coarse grain, (and in a ca-
binet specimen scarcely discernible) but which becomes gradually
more distinct as the texture becomes finer, and at last the rock
graduates into a fine grained slaté, divisible into laminz as thin as
paper, and having the smooth silky feel and shining surface of the
clay slate of a primary country. Alternations of the fined grained
slaty varieties with those of the coarsest structure in many successive
strata and without any regularity of position, are of constant occur-
rence, and frequently without any gradation from one structure into
the other.* In some instances portions of slate are contained in
the coarse grained varietiés. Scalés of mica are frequent, and they
all contain oxide of iron in greater or less proportion, and to the
different states of this oxide their various colours are, no doubt, to
be ascribed. The prevailing colours are reddish brown and green-
ish grey, and'there are many intermediate shadés and mixtures of
these colours. Some of the slaty varieties are of a purplish hue,
and this is occasionally spotted with green. Of the specimens I
collected, those of a coarse grain and of a dark reddish brown
colour, do not effervesce with acids; those of a pale reddish brown
colour, and of a greenish grey colour, all effervesce, and some of
them briskly. None of the varieties of slate shew any signs of
effervescence: The magnet was not affected by any one of the
series. I did not discover a trace of any organic body in either

* Similar alternations. of clay. slate with grauwacke Rage been observed at Crinan
and at Aberfoyle, by Dr. Mac Culloch. (Transactions of the Geological Society, Vol.

If. p. 441, 447.) and by Mr. Jameson in the Pentland Hills. (Memoirs of the Werne-
rian Natural History Society, Vol. II. Part I. p. 184.)

344 Mr. Horner on the Geology of the

variety, but in many places great beds of limestone full of madre-
pores, are contained in the slate, the limestone and slate to-
wards the external part of the beds being interstratified. Veins of
quartz, which are often of great magnitude, are of constant oc-
currence, being sometimes accompanied by calcareous spar and
ferriferous carbonate of lime; veins of sulphate of barytes are
not uncommon. Thin layers, composed of quartz, chlorite, and
ferriferous carbonate of lime, are often interposed between the
strata of slate, and pyrites is sometimes disseminated through the
mass of the rock. Copper, in the state of sulphuret and of ma-
lachite, and veins of hematite, are frequently found, and nests of
copper ore of considerable magnitude have been found in the
subordinate beds of limestone. |

Those who are acquainted with the geology of Devonshire and .
Cornwall will recognize in these characters a great similarity be-
tween the rocks which I have been describing, and those which
form so large a portion of the western counties, and which have
of late been designated by several mineralogists by the term grau-
qwacke. Jam fully aware of the unwarrantable extension of this
name, and of the great want of precision which has been the con-
sequence of applying it without pointing out the mineralogical
structure of the compound; but I feel in common with many
others the difficulty of finding a less objectionable term by which
the series of rocks in question may be distinguished, when it is
necessary to speak of them collectively. As the word by itself
conveys no theory, and as these rocks have a closer connection
with that class to which the term was originally applied than with
any other, I shall call the series of rocks which I have described,
a grauwacke formation, hoping that the description I have given
will, in some degree, remove that want of precision which is the

South-Western Part of Somersetshires 345

chief objection to the word. ‘To those however who may give to
it the theoretical meaning which this word implies in the Wernerian
system, I must again point out the alternations of quartz rock,
and of a clay slate, with beds of limestone full of organic remains.
The clay slate cannot be distinguished from that of a primitive
country.

§ 5. A reference to the accompanying map will serve better
than any description to shew the extent of country occupied by
this formation: it remains for me to point out some of those cir-
cumstances connected with it which appear to be worthy of more
particular notice. ;

The north hill which extends soda the shore from Minehead
to Porlock, forming a very bold and precipitous coast, affords the
best opportunity of studying this grauwacke formation. At
Greenaley point, about a mile westward of Minehead, there are
very lofty sections where the alternations of the different varieties
may be distinguished, and where there are also very good examples
of those curvatures, which, in this formation, are of such frequent
occurrence. Strata that run for some distance in a horizontal line
suddenly turn up into a vertical position, at other times they assume
the form of an arch ora succession of great curves. It is hardly
necessary to say that these rocks could not have been deposited in
the forms they now exhibit, and it is pretty evident that the flexures
must have taken place while the rock was in a plastic state, for:
there is no fracture at the bendings, nor any interruption to the:
continuity of the mass. Similar curvatures are to be seen at Hur-
stone point, the western extremity of North hill. These appear-
ances are so well known that drawings of them are unnecessary :
they are very analogous to those observed by Mr. Conybeare in
the same rocks on this coast, some miles westward, and repre-

VOL, III. a2) x

346 Mr. Horner on the Geology of the
sented in the 33d and 34th Plates of the 2d. Volume of the So-

ciety’s Transactions. :

§ 6. In every part of the district where the slaty varieties pre-
vail, the ends of the inclined strata as they rise to the surface be-
come either vertical or are very much twisted. Here however the
contortions appear to have taken place after the induration of the
stone, for they are not in the form of curyes, but are in ge-
neral a succession of sharp angular twistings, with a fracture at
every angle. The strata in general as they approach the surface
are also very much traversed by those imperceptible cracks which
make the rock, as soon as it is moved from its bed, break down
into polygonal fragments of various dimensions. Hence are pro-
bably derived those loose fragments which are to be found under
the surface soil all over the district where this formation occurs, and
even at the summits of the highest hills, In the ravines formed by
the streams in the lower parts of Dunkery beacon, there are sec-
tions of some yards in depth where nothing is seen but these frag-
ments, imbedded in a loose red sandy soil, which is doubtless pro-
duced from the decomposition of the fragments themselves. The
angular shape of the fragments is an additional proof that they have
been produced on the spot, and that they are not materials trans-
ported from a distance. The most remarkable instances of these
angular contortions are to be noticed in the lanes between the vil-
lage of Enmore and West Monckton, and the other roads which
cross the south-eastern ridges of the Quantock hills. I may par-
ticularly point out the neighbourhood of Adsborough, and the
lane leading to Tarr near Kingston, where the ends of the strata of
slate are covered by horizontal beds of red argillaceous sandstone
and of conglomerate.

§ 7. In a country covered by vegetation, and where the rock is

South-Western Part of Somersetshire. 347

so liable to partial irregularities, it is exceedingly difficult to form
any general conclusions as to the bearing and dip of the strata:
Every geologist must have observed that the external shape of a
hill is not always a certain guide in determining the bearing of the
strata that compose it, and that in many places other causes must
have operated in producing the external forms which the earth now
éxhibits. I believe however that the general bearing of the
strata In question may be stated to be between east and west, and
that the dip is more generally to the south than to the north.

§ 8. In the ridge which terminates at North Petherton, there
are at Binfords some very large quarries where the gradation of
one variety of rock into another may be seen. In the lower part
of one of the beds there is an accumulation of rounded masses of
an oblong shape, varying in size from a, few inches to several feet,
in the direction of what may be termed their longest diameter.
Their internal structure is often identical with the adjoining strata
of grauwacke, but they more frequently consist of a succession of
thin concentric layers, these layers being of the same substance
with the strata, but separated from each other by a thin coating of
oxide_of iron, having the shining lustre of hematite. The smaller
of these masses more nearly resemble a large mytilus than any
other shape to which I can compare them, and the larger of
them preserve nearly the same form. They appear to have been
consolidated while the rock in which they are imbedded was in a
soft state, for the surface of the bed on which they rest is covered
with the moulds of those that have been removed.

§ 9. Near Ely Green in the side of a combe called Dibbles,
towards the summit of the Quantock hills, I observed a variety of
slate differing considerably in appearance from any I met with in

the district except in one other spot. It is of a bluish green
Z2x@Z

348 Mr. Horner on the Geology of the

colour, apparently derived from chlorite, with purplish stains
and including small -spherical masses of a white earthy tex-
ture, which give to the mass an amygdaloidal structure: it may
-be considered as a variety of argillaceous slate, and as it occurs
in strata conformable with the usual varieties of the grauwacke
formation, it belongs I have no doubt to the same class: it is
found to be very useful as a fire stone. The other place where
{ found a slate very similar to this was in the neighbourhood of
Cheddon Fitz-Paine.

§ 10. In passing through the village j ust named, I observed in
the street a small block of stone differing in appearance from any
I had found previously, and upon examination I found it to be
granite, a rock I had searched for before without success, and in-
deed this is the only place where I saw an unstratified rock in the
whole district, the porphyry and greenstone which accompany the
grauwacke formation in Devonshire being wholly wanting here.
On inquiry I found that this granite, called by the country people
Pottle Stone, came from an old quarry not far distant in the grounds
of Hestercombe, belonging to T. Warre, Esq. My informer
brought out of his house a whetstone which he said came from
another quarry close by the Pottle Stone. It was a greenish com~
pact stone, very like some hornstones or some of those close-
grained siliceo-argillaceous compounds which it is very difficult to
name. On going to the quarry, which is almost entirely over-
grown with brushwood, I found the granite im sitw: it is small
grained, and consists of dull flesh-coloured felspar, with green
mica, and a small quantity of quartz. It occurs in the lower part
of the hill and occupies a very limited extent. Immediately ad-
joining is the spot where the whetstones are got. Here I found
regular strata of slate similar to that occurring in many parts of

South-Western Part of Somersetshire. 349

this district, inclined at a considerable angle and rising towards a
mass of the granite which appears in the form of a wall a few feet
above the ground. Within a few yards of the granite the incli-
nation of the strata is about 35°, but as it approaches nearer to it
the angle increases to 63°, and the texture of the stone becomes
much more compact; the actual junction of the two rocks is, as is
usually the case, very indistinct, the stratification of the slate be-
ing very much disturbed and broken: but I was informed that the
best whetstones are got nearest the granite, and I found the most
indurated pieces in that situation. Being desirous of seeing the
actual contact, I obtained permission from Mr. Warre to clear
away the ground across the line of junction: and although the
quantity of brushwood, and thick covering of soil, and a very
unfavourable state of the weather prevented me from making so
complete an examination as I wished, I so far effected my purpose
as to find the junction. ‘The granite as it approaches the slate be-
comes much finer grained than before, and at the contact there is
an indistinct blending of the two, and as far as I can judge from
the very imperfect specimens I could obtain, there is an appearance
of fragments of the slate united by a granitic cement. All the
circumstances appear to favour the supposition of this being a
vein of granite, but the evidence I have to offer is too scanty to
enable me to speak with confidence on the subject.

§ 11. Some years ago a shaft was sunk in one of the branches
of Grabbist hill at Stanton, above the village of Alcombe, in
consequence of some indications of copper in the rock there, but
the quantity of ore found was so small that the workings were very
soon given up. I found among the rubbish some pieces of green
carbonate of copper with grey copper. Similar trials with no
better success were made at Perry near the northern extremity of

350 Mr. Horner on the Geology of the

the Quantock hills. I found there, among the rubbish, specimens
of malachite and of brownish-black sulphuret of copper.

I received from Thomas Poole, Esq. of Nether Stowey, a spe-
cimen of an exceedingly hard and compact iron ore which had
been found in the Quantock hills, but in what place he could not
inform me. It is an oxide of an iron-grey colour and semi-me-
tallic lustre, with a sharp splintery fracture, and so hard as to
scratch glass easily. Its specific gravity I found to be 5.244, which
with its other characters brings it nearer the fer oligiste of Hatty
than any other variety of ore. The occurrence of so rich an ore
in a large quantity, would be a very valuable discovery.

§ 12. In several parts of this district there are found, as I have
already stated, very considerable beds of limestone which are con-
tained in the slate. Their occurrence in detached spots, and their
appearance in the quarries where they are most extensively
wrought, seem to point out that they are not regular strata con=
formable with those of the slate above and below them. Flattened
spheroidal masses of the same kind of limestone are frequently
found, completely enveloped by the slate, and very similar to the
balls of clay-iron-stone in slate clay, but thinning away at the
edges much more than those do. I conceive that the great masses
of limestone occur in the same way : they have an irregular bedded
structure, and very often layers of slate, often of considerable
thickness, are interposed between the beds; but although the
positions of the quarries along the eastern side of the Quantock
hills appear in a continuous line on the map, the great variations
in the bearing and dip of the strata of those quarries renders it
extremely improbable that the limestone of each, although very
similar, are parts of regular strata. ‘These beds of limestone ap-
pear to be confined to the places where the slaty varieties of grau-

South-Western Part of Somersetshire. 351

wacke formation prevail ; I shall now point out some of the most
extensive quarries where they are worked.

§ 13. At Allercot, about four miles south of Minehead on the
road to Dulverton, the principal bed of limestone is 30 feet thick.
It is of a bluish grey colour, variegated with red, of a crystalline
structure, and full of small laminz of calcareous spar disseminated
in detached spots through the mass, which are most probably the
remains of organized bodies. Besides this great bed, there are
several others of less thickness contained in the slate, and the thinner
beds are of an iron-grey colour. The slate is one of those fine
grained varieties which approach very nearly in appearance to the
clay slate of a primary country ; it is very much contorted, and the
curvatures are often so small as to be seen in a cabinet specimen.
Is is very much traversed by veins of quartz. I was informed by
the workmen at Allercot that there are quarries of a similar kind of
limestone at Westcot, Treborough and Leigh. At Treborough a
very excellent roofing slate is obtained.

§ 14. At Doddington, Friern farm, and Ely green, on the
eastern side of the Quantock hills, the quarries are very extensive.
In those of Friern farm I found some of the beds to be a very close
grained crystalline limestone without the slightest appearance of any
organic remains; but upon a close examination of the stone when
broken in different directions, and particularly at those places where
it is bruised by the stroke of the hammer, I found many parts of
the bed to be almost entirely composed of a madrepore. ‘Towards
the exterior, madrepores are very distinctly seen, and in some of
the beds the stone is full of circular bodies composed of large
crystalline plates of calcareous spar, which I have little doubt are
entrochi, but I did not discover a shell any of description.

352 Mr. Horner on the Geology of the

§ 15. In the quarries at Great Holwell there may be seen on a
small scale that occurrence of caverns so frequent in limestone.
They vary in width from half a foot to five feet, and their height
varies with the thickness of the beds. In some places they may be
seen to close, but in general their depth was beyond what I could
ascertain. ‘Their sides although uneven by the irregular projections
of the rock have all a smooth rounded surface, as if worn by attri-
tion, but this seems to be owing to an incrustation of calcareous
spar which hangs down in many places in large stalactites, a process
that is evidently going on at the present time in several of these
caverns. That the caverns have not been produced by any rents
that might have occurred after the consolidation of the strata, is
evident from their being confined to the limestone and not extending
through the intervening slate.

§ 16. Nests of copper are very frequently found in this lime-
stone. I observed in several places small nodules of the green
carbonate enveloped by brown ochreous earth. At Doddington a
very large quantity was found some years ago. A loose friable
quartzose sandstone, which I shall afterwards notice, was found to
contain so much copper ore that a mine was sunk in it. In order to
drain the works which were situated upon the rise of the hill, a shaft
was sunk for the purpose of driving a level from north to south up to
the workings, expecting at the same time to cut across any veins of

metal that might exist there, as they are generally supposed in this:

part of the country to run east and west. ‘They had proceeded a
very short way in driving this level when they came upon a black
slaty limestone, and immediately afterwards they found a large nest
of copper ore, consisting of the green carbonate, and yellow sulphuret.
‘The workings in the sandstone were immediately given up; they

Bl
; a

South-Western Part of Somersetshire. 353

did not continue driving the level, but worked in the limestone on
all sides. The mine has however been abandoned, as the produce
was not sufficient to bear the expence of an engine to drain off the
water.* | 20°

§ 17. I found specimens of the black slaty limestone at the
mouth of the pit, and I afterwards observed the same stone in the
limestone quarry near Ely green’ interposed between the beds of
limestone. It is of a coal black colour, but becomes white when
heated: dissolved in muriatic acid it leaves a black powder, and this
powder when heated is partly dissipated, and what remains is a white
earth. The limestone appears therefore to owe its black colour to
carbonaceous matter. ;

Besides the quarries I have named there are several others, but
as they present no appearances different from those I have already
described, it is not necessary to do more than mark their occurrence
on the map.T'

§ 18. About a furlong eastward of Halsey cross, in a quarry
where stones are obtained for mending the roads, I found strata of
the coarse grained and slaty varieties of the grauwacke formation,
alternating with a calcareous rock different from any other I had
seen in this district. Its colour is in general reddish brown, very
similar to the strata that alternate with it, but the calcareous strata
are not all alike. In none of them are there any traces of organic
remains, unless indeed some detached crystalline lamine may be
considered as indications of them. The principal varieties are

* Treceived this account of the Doddington mine from my friend Thomas Poole, Esq.
of Nether Stowey.

+ The position of many of those quarries has been pointed out to me by my friend
the Rev. John Poole of Enmore, to whom I am indebted for much valuable assistance in
the prosecution of this inquiry.

VOL. iil. Qy

354 Mr. HorNneER on the Geology of the

1. A crystalline limestone which burns to a white lime mixed
with brown spots, falling very readily to powder. 100 grains
dissolved in dilute acid left 7 grains of residuum, which con-
sisted of about 4 grains of oxide of iron, the remainder being
silica.

2. The preceding variety mixed with a considerable quantity of

quartz, and of yellow calcareous spar. This latter substance

occurs also in veins and probably pervades all the calcareous
strata. A piece of that stone when thrown into dilute acid
leaves a fragment which does not fall into powder.

This variety is intermixed with a smooth slaty substance with

gs

an unctuous feel, which is probably talcose slate: it leaves a
considerable quantity of large grains of quartz when thrown
into dilute acid.

None of these calcareous strata are used for any other purpose
than to mend the roads, and they do not seem to be known as
limestones, most probably because there is a much better limestone
so near at hand. ‘The first variety would yield a very good lime,
if reliance for that: purpose can be placed on my minute expe-
riments:; a trial on the large scale might very easily be made in one
of the neighbouring lime kilns. The principal calcareous stratum
is five feet thick.

Immediately behind the village of Bagborough I found a calcareous
stratum occurring in the same way as those at Halsey cross.

§ 19. My observations were principally confined within the
limits I have already mentioned, but having had an opportunity of
making a cursory examination of the country between Porlock and
Ilfracombe, and as the rocks occurring in that part of the country
are connected with those I have been describing, I shall briefly state
the few notes I made. My route was from Porlock, by Culbone,

South Western Part of Somersetshire. 355

Withycombe farm and Countesbury to Linton, and from thence
through the Valley of Rocks by Slattenslade, Trentishoe, Combe
Martin and Berry Narbor to Ilfracombe. A very great part of this
country is entirely concealed by vegetation, but wherever the rock is
exposed I found some variety of the grauwacke formation identical
with those I had left behind. In that part of the road which is east-
ward of Linton, the coarser grained varieties are most frequent, but
westward of that place the slaty varieties predominate, very often
resembling some kinds of iron-grey clay-slate found in primary
countries. Towards Ilfracombe this appearance becomes still more
decided, and in-a cabinet specimen it would be impossible to tell
the difference. But beds of limestone with very decided indications
of organic remains contained in this slate, show that it is of secon-
dary formation, and at the same time afford a useful lesson of the
inadequacy of mineralogical characters alone to determine the
geological nature of a rock. These limestone beds are found
between Berry Narbor and Hele; their resemblance to those I have
described in the former part of this paper both in internal com-
position and in the accompanying slate, leave no doubt of their
belonging to the same class. When struck with a hammer it emits
a slight bituminous smell, a circumstance which I did not observe
in the limestone of the other places I have mentioned, and it is
traversed by very large veins of a transparent and very beautiful
calcareous spar.

§ 20. Throughout the whole district described in this paper
I found the grauwacke formation surrounded either by a conglo-
merate, or by a red sandstone, sometimes tolerably compact, but
more frequently of a friable texture. These conglomerates and
sandstones assume very various appearances, but under every form
of aggregation the same materials may be traced. Where the

2.Y12

2

356 Mr. HORNER on the Geology of the

component parts are large, as in the conglomerates, the nodules
consist of some of the varieties of rock that compose the grauwacke
formation, and in many places there are nodules of a limestone very
similar to that of the subordinate beds in the same series. These
derivative rocks under one form or another are found in all the
intervening valleys, and the great valley on the western side of the
Quantock hills is wholly composed of them. They are not how-
ever confined to the vallies, but are sometimes found on the sides
of the hills at a very considerable elevation. It would have been
a fruitless task to have attempted to distinguish in the map each
particular form of aggregation, more especially as I did not discover
any uniformity in their relative positions. I have thought it better
to class the whole under one head and to represent them as such
by one colour. It will be necessary however to point out in detail
_some of the most remarkable instances.

§ 21. In the eastern and highest part of the valley in which the
village of Porlock is situated, there is found at Tivington, Huntsgate
and Holt farm, a conglomerate composed of thin fragments of a
coarse grained siate seldom exceeding an inch in size, with pieces
of quartz, cemented by white calcareous spar. The surfaces of the
fragments are rounded by attrition, and are coated with reddish
brown oxide of iron, which has in many places the metallic lustre
of hematite. The fragments are in some places so small that the
rock has the appearance of a sandstone. It occurs in thick beds
which are often inclined at a considerable angle, but not conform-
able with the slope of the hill in the lower part of which the con-
glomerate is found. The smaller grained rock frequently alternates
with the coarse conglomerate: at Tivington the latter variety prevails,
but at Huntsgate that resembling a sandstone forms the thickest
beds. Both varieties are very much traversed by veins of calcareous

South-Western Part of Somersetshire. 357

spar. At Holt farm there is a vein nearly 18 feet thick, consisting
of several layers so distinct that I at first conceived the mass to be a
series of strata, but upon further examination I found that it was
inclined at right angles to the dip of the beds of conglomerate. It
is stratified not only on the great scale, but also in the internal struc-
ture, which consists of a succession of layers, having in many places
a waved appearance similar to that seen in sections of recent cal-
careous depositions. Part of this vein consists of a mixture of white,
red, and honey-yellow calcareous spar, resembling in some places
cellular quartz. The quantity of calcareous matter in this con-
glomerate is so great that it is quarried for the purpose of obtaining
lime from it. But at Holt farm, the great size of the vein renders
it unnecessary for them to use the less pure conglomerate,

§ 22. In the lane leading from the town of Minehead to the
church, which is situated near the eastern termination of North
hill, the rock has been cut through to a considerable depth. At
the first part of the ascent it is a friable red sandstone distinctly stra-
tified, and dipping north-east by north about 15° as it were into
the hill. It is almost entirely siliceous, and contains no calcareous
matter, nor are there any of those grey patches which generally
accompany the marly red sandstone to be afterwards described. It
appears to rest upon a conglomerate, that rock just appearing above
ground. Continuing to ascend, this red sandstone after a short way
is suddenly broken off, and is succeeded by a conglomerate which
continues during the remainder of the ascent, till it meets the grau-
wacke formation immediately above the church: unfortunately the
actual contact isnot exposed. This conglomerate consists of rounded
fragments of rocks identical with those found in the grauwacke
formation, but without any limestone. In different parts of it there
are patches of the same red sandstone that occurs in the first part of

358 Mr. Horner on the Geology of the

the ascent, varying from a few inches to several fathoms in extent,
and having in general a stratified structure.

§ 23. Near the village of Alcombe, and at the foot of one of
the lateral branches of Grabbist hill, there is found a conglomerate
differing considerably from either of those already described. It
occupies a very small space superficially, probably not more than a
square furlong, but it is found in very thick beds. It is composed
of rounded fragments of the coarser quartzose varieties of the grau-
wacke series, of limestone and of quartz, united by a calcareo-argil-
laceous cement of a reddish brown colour. The limestone is in
general grey with a reddish tinge, of a crystalline texture, with
laminz of calcareous spar scattered through it, and frequently con-
taining carbonate and sulphuret of copper; characters sufficient to
identify it with the subordinate beds of the grauwacke formation.
In one or two instances I found it containing chert. In some parts
of the conglomerate the cement is very much mixed with white and
flesh coloured sulphate of barytes in crystalline plates, and with
green carbonate of copper. It is also traversed by veins of calcareous
spar, and contains cavities lined with crystals of the same substance.
The fragments are of different sizes; some of them are as large as a
man’s head. ‘The conglomerate is covered by a loosely aggregated
quartzose sandstone, varying in colour from reddish white to brown-
ish red, and often containing much calcareous matter. Sometimes
there are fragments of the same varieties of grauwacke that occur in
the conglomerate, found in those parts of the sandstone that are
contiguous to it; and it is also mixed in some places with green
carbonate of copper and with sulphate of barytes. In the upper
part of the conglomerate there are rounded fragments of a sandstone
mixed with carbonate of copper nearly identical with that of the
beds lying over the conglomerate. This sandstone is about 5 or 6

South Western Part of Somersetshire. 359

feet in thickness, and dips northward about 18°. The signs of stra-
tification are not very distinct in the conglomerate, but the beds
appear to dip at the same angle and towards the same point as the
superficial sandstone. This conglomerate is called Pofple rock
(Pebble?) by the quarriers, and is worked on account of the nodules
of limestone, which are picked out and made into lime.

» § 24. Opposite Bickham farm near Timberscombe, and at the
foot of the hill which may be considered the eastern termination of
Dunkery beacon, another modification of the conglomerate occurs.
It is composed of large irregularly-shaped flat masses of limestone
imbedded in a pale green sandy clay. Between these masses there
is interposed a conglomerate of smaller sized fragments, very analo-
gous to that found at Tivington, and the whole series is covered by
a friable red marly sandstone. The limestone is similar to that
found in the conglomerate at Alcombe. The lower part of the
valley on the south side of Grabbist hill is chiefly meadow land,
but in some places where the ground is broken, as in the road
near Wotton Courtney, and in the road from Timberscombe te
Minehead, I observed a red marly sandstone with grey patches con-
taining thin strata of a small sized very compact breccia composed of
fragments of a white indurated clay, united by a cement of clay
mixed with calcareous matter, and here and there small cavities in
it lined with calcareous spar. This compound I did not find in any
other part of the district.

§ 25. The valley which separates the Quantock hills from the
mountainous country to the west does.not present a uniformly even
surface: there is along its whole extent a succession of low hills
having a longitudinal direction: parallel to that of the valley. ‘There
are two ranges of these hills, but the most conspicuous are on the

side of the Quantock hills. The whole of this valley is occupied

360 Mr. Horner on the Geology of the

by the derivative rocks I have been describing, and all the different
modifications to be found in the district occur in this valley, and
the whole of the low hills are composed of them. In the bottom
of the valley there is a considerable tract of loose sand. On leaving
the grauwacke series near Dunster, we find at Carhampton a low
hill composed of a red argillaceous sandstone, and proceeding east-
ward towards Williton, either that sandstone, or a sandstone con-
taining rounded fragments of the grauwacke formation appears in all
those places where the ground is broken. At Tarr, Tor Weston,
and Vellow, the same conglomerate (or pebble rock) that I have
described at Alcombe, again appears. At Tor Weston the quarries
are situated near the top of a small detached hill, the conglomerate
forming beds of great magnitude. At Vellow there are sections of
it above 50 feet in height, and it rests here upon a bed of red clay.
There are distinct parallel lines which divide it into thick beds,
dipping northward about 10°. It contains here more fragments of
limestone than it does at Aleombe, and I found between the pebbles
in some places, small nests of hematite. It is covered as at Alcombe
by a sandstone, but of a different variety, being of a deep reddish
colour and full of fragments of grauwacke, and without any appear-
ance of copper or of sulphate of barytes. The same sandstone may
be seen in different places between Williton and Vellow, particu-
larly near the village of Sampford Brett. A little to the west of
Williton church, there is a reddish white sandstone, much harder
than any other I met with in this district. It occurs at the eastern
termination of the same ridge, on the west side of which the quarries
of conglomerate at Tarr are situated, and I think that it is very pro-
bably only a variety of that sandstone which covers the conglomerate
in other places. If it is stratified the lines of separation are very
indistinct. ‘There are many perpendicular fissures in it; part of

South-Western Part of Somersetshire. 361

which are filled with a pulverulent carbonate of lime. It is very
durable when used for building, and Watchet Pier has been repaired
with it. The Popple rock of Vellow extends as far as Yard farm, and
T observed it in the road near Quark-hill farm on the eastern side of
the brook.

§ 26. At Lawford farm near Crowcombe there are some large
quarries where different varieties of the derivative rocks may be
seen. The conglomerate, besides its usual component parts, is ac-
companied by patches of a green sandy clay, similar to that in the
quarries near Timberscombe, and I may remark here that these
green patches are prevalent in almost all the forms of .conglo-
merate on the south and south-east slopes of the Quantock hills.

The conglomerate at Lawford farm is covered by several beds
of red sandstone, which are in general separated from each other by
a layer of rounded fragments of grauwacke mixed with red earth.
‘There are also several beds of conglomerate which are separated by
beds of sandstone, lying nearly horizontal: some of the sandstone
beds give more lime than any other in the quarry. This series of
beds extends for some distance towards Lydeard St. Lawrence by
Crowcombe Heathfield, and is succeeded near that town by red
sand. | |

§ 27. A road is carried along the side of the Quantock hills
from Crowcombe to Bagborough by Triscombe. ‘The derivative
rocks prevail all along this road, although it is at a very considerable
elevation: this is the greatest height at which I found them, ex-
cept in one place on the eastern slope of the Quantock hills, avd
near the summit of the range, at Quantock farm ; where in digging
a foundation there was found below the surface soil a conglomerate,
consisting of rounded fragments of grauwacke cemented by a deep
red clay, forming a mass of extreme hardness. A short way south

VOL. i1F. 22

362 Mr. Horner on the Geology of the

of Triscombe the conglomerate appears, and may be traced to Bag-
borough and from thence the whole way to Bishop’s Lydeard, where
sections of it are seen-in the side of the road.

§ 28. I have every reason to believe that nearly the whole of
the rich vale of Taunton Dean is formed of rocks of this descrip-
tion. Mr. De Luc* describes a “ red marl with blue stripes” be-
tween Blackdown and Wellington, and in the neighbourhood of
Wiveliscombe he observed “ at the summit of two eminences” a
conglomerate in all respects the same as the Popple Rock of Vellow,
which he afterwards examined. ’

§ 29. Near the village of St. Michael the road is cut across a ridge,
and exposes a section of conglomerate and red sandstone to the depth
of 20 or 30 feet, and the same rocks are found in all the intervening
vallies between the ridges of the grauwacke formation which extend
from Cothelstone Lodge in a south-easterly direction. The road
from Bridgwater to Nether Stowey crosses the extremities of some
of the lateral branches that extend from the Quantock hills, and
these are entirely composed of the derivative rocks. Near Coke-
hurst, at a place called Mount Radford, there are some large quar-
ries where a very hard conglomerate is worked. In composition
and alternation with sandstone it is very like the series at Lawford
farm, and like that contains green patches. It occurs in thick beds
which are inclined at an angle of 15°. dipping north by west. In
one of the quarries I observed a slip in the beds of about four feet,
and the sides of the slip were covered with a smooth coating of
oxide of iron similar to a slickenside. Within a mile of Stowey,
where the road turns off to Taunton, there is a sandstone which is
principally white, but is in some places variegated with red spots
and stripes, and containing some of those green patches so general

* Geological Travels, Vol. 3. § § 1349 1351.

South-Western Part of Somersetshire. 363

in the conglomerate. In some places it is very friable, in others it:
forms a hard stone, in thin strata dipping gently to the north and fol--
lowing the inclination of the hill. Near Bincombe and Doddington
it is also found, and in both those places it is very white and friable,
and contains a great deal of green and blue carbonate of copper, the
latter often beautifully crystallized. It was in this sandstone that
the mining near Doddington, already mentioned, § 16. was begun.
Near Ely Green it is mixed with large red patches, which are very
argillaceous, and are chiefly composed of angular fragments of grau-
wacke; at the bottom of the section the sand becomes more com-
pacted and seams of stratification are distinct. This sandstone I
conceive to be the same as that which lies upon the conglomerate
at Alcombe. x

§ 30. Besides the conglomerates and the sandstone that accom-
pany them, there isa member of the same series which requires to
be more distinctly pointed out. It is a red argillaceous sandstone,
containing a variable quantity of calcareous matter, but its most cha-
racteristic feature is its being always accompanied by spots and stripes
of a greenish colour. These greenish parts are of all sizes, from a mere
speck to such a degree of magnitude that they often exceed the red
portion of the rock, and when this is the case they become much
more indurated, and contain a larger proportion of carbonate of
lime. There is seldom any marked line of boundary, the passage
from the red to the greenish parts being quite gradual: it is occa-
sionally variegated with yellow, and those places abound with den-
dritical delineations of manganese. It is of a uniformly fine tex-
ture, and I never found it to contain any fragments, either angular
or rounded. It is the same rock which covers so great a portion
of the Midland counties of England, which contains the gypsum of

222

364 Mr. Horner on the Geology of the

Derbyshire and Staffordshire, the salt mines of Cheshire, and the
brine springs at Droitwich in Worcestershire, and whichis known
by the name of red marl, red ground, &c. There are few rocks
which present a greater variety of forms of aggregation, and about
which there are so many contradictory opinions respecting its rela-
tion, in point of position, to the other secondary strata that lie
contiguous to it. ‘To investigate the mineralogical and geological
history of this rock would be a most useful inquiry, and not merely
as a matter of science, but in an economical point of view, from its
intimate connection with thecoal formations. There is undoubtedly
in the district [ am now describing an appearance of this rock having
a common origin with the other varieties of the derivative rocks, as
a series could without difficulty be collected, shewing an insensible
gradation from the one to the other, and the patches of greenish
sandy clay I have mentioned in the conglomerates § § 24, 26, are
another strong point of resemblance. It never has been ascertained,
I-believe, what is the chemical difference between these greenish
grey patches, and the red rock into which they seem to graduate.
In many other places this red marly sandstone is accompanied by
similar conglomerates, and I observed in the collection of my friend,
G. B. Greenough, Esq. a specimen from Alderley Edge, in Cheshire,
identical with that variety of conglomerate found at Alcombe, § 23,
which contains sulphate of barytes, and carbonate of copper.—
Although I found it always above the conglomerates in this district, I
am informed by Mr. Greenough, that this is by no means a general
rule. In that part of the district which I have already described it
occurs to a very limited extent in point of thickness, but on the sea
shore in the neighbourhood of Watchet, it forms, as I shall presently
shew, a very prominent feature in the mineralogy of this part of
the country. I found it in almost every situation where the deri-

South-Western Part of Somersetshire. 365

vative rocks occur, and at their greatest elevation as at Smokeham,
Crowcombe and Bagborough, but it appears to lie always above -
them. I did not find it in any one instance covered by the con-

glomerates or their accompanying sandstones.

§ 31. In the eastern part of the district near the banks of the
Parret below Bridgwater there is a nearly insulated hill called Can-
nington Park, totally different in structure from any other part of
the country described in this paper. On the north side it rises di-
rectly from the marsh land, with a gradual slope, to the height of
232 feet above the plain: on the south side it is not altogether cut
off from the lateral branches of the Quantock hills. It is composed
of a highly crystalline limestone, of a pearl grey colour, having a
very close grain, and when struck, giving a ringing sound like that of
glass. I examined it with very great care, in order to discover
whether it contained any organic remains, and particularly at the
decomposed surfaces, and in those places where the stone was
bruised by the blow of the hammer, which generally detects any
madrepores that exist in a limestone, but I could not find the slight-
est trace; and some of the quarriers who had worked there for
several years, told me that they had never found any thing of the
kind. It contains here and there contemporaneous veins of a very
pure white and opake calcareous spar, and the strata are traversed by
large veins of calcareous spar. In the latter veins the spar is dis-
tinctly crystallized, and in layers parallel to the sides of the vein, a
circumstance which points out a marked difference between them
and the veins of contemporaneous formation. On the north side of
the hill there is a vein of red sulphate of barytes, about three feet
thick in the widest part. This substance is not contiguous to the
limestone, but is accompanied on each side by a reddish brown
ochreous earth. Nor does the vein itself appear to intersect the

366 Mr. Horner on the Geology of the

limestone, but to be interposed between two vertical masses. The
barytes contains copper pyrites and green oxide of copper, and in
the limestone near the vein I found quartz crystals scattered through
the mass, giving it an appearance like a porphyry. I also observed
in some places traces of carbonate of copper in the limestone.

§ 32. In going over the top of the hill (which is very much
covered by vegetation) the ends of the strata appear above the grass
in many places in a vertical position, and running between north-
east and south-west, but on coming to the quarries where the rock
is extensively exposed, I found that although it is evidently stratified,
it is so shattered and so crossed by rents in every direction, that it
was impossible for me to discover what were the true planes of stra-
tification, the internal structure of the stone affording no indication.
Judging however from the more general direction of the masses, I
think they may be said to be either for the most part vertical, or at
least very highly inclined and running between north and south. I
did not discover the least appearance of slate or any circumstance
that could connect this limestone with the subordinate beds in the
grauwacke series of the neighbouring hills, except its proximity to
them. It more nearly resembles the Plymouth limestone than any
other I am acquainted with, and although that has been found to
contain both madrepores and shells, there are great portions of it
where no traces of organized bodies can be discovered. It is also
very probable that by a more minute examination they may be
found in the limestone of Cannington Park, for it has certainly
very much the appearance of what is called a transition limestone,
and there are laminz of calcareous spar dispersed through it, which
are strong indications of organic remains. It produces a very pure
white lime, which is carried to a great distance.

§ 33. From the termination of the marsh land which lies to

South-Western Part of Somersetshire. 367

the east of Minehead to that at the mouth of the river Parret there
is a rocky shore, bounded by precipitous cliffs, rising in many.
places to the height of 100 feet. These are chiefly formed of that
variety of secondary limestone, so well known by the name of
lyas, together with the red argillaceous rock described § 30. The
boundaries of these rocks will appear by inspecting the map, and I
shall now point out the more remarkable circumstances connected
with each. The great disturbances which have taken place in the
strata render it extremely difficult to ascertain with precision the re-
jative positions of these two rocks. When I first examined the
coast, I observed what I conceived to’be the most distinct evidence of
the red rock alternating with the lyas: but as this was an important
point to ascertain, being at variance with all observations in other
places of the position of the lyas and red rock which I had heard of, I
repeated my examination of the ground with great care, and I think
it is probable that the apparently very distinct alternations of the
lyas strata with the red rock are deceptions produced by those
curvatures and dislocations so common on this coast, as I shall
shew when I describe those places. This lyas is an argillaceous
limestone of a dull earthy aspect, with a large conchoidal fracture,
and generally of a light slate blue colour. It occurs in very regular
strata which seldom exceed a foot in thickness, and are often not
more than four inches: they are separated from each other by strata
of slate clay, varying considerably in thickness. All the strata of this
limestone, though externally very similar, are not of the same mine-
ralogical composition, for they have very distinct properties. Some
of them yield a lime which possesses in a most eminent degree the pro-
perty of setting under water: these are generally the thinest strata,
are of a light blue colour and compact earthy texture; on each sur-
face of the stratum, and at the joints the colour is changed to a light

368 Mr. Horner on the Geology of the

brownish yellow or cream colour, which is of different thicknesses,
in some places extending so far into’ the interior of the stratum that
the blue colour is nearly obliterated. I very rarely found organic re-
mains in these beds.

§ 35. ‘The other variety of the limestone is of a much darker
colour, but is most particularly distinguished by the strong fetid
smell it gives out when struck by the hammer, and when it is burn-
ing inthe kilns. It is always in thicker strata than the other variety
and abounds in organic remains, it is also very much penetrated by
pyrites in many places. These fetid strata have much less the property
of setting under water, and are best adapted for agricultural pur-
poses, for which the other are very unfit. The quarriers on the
spot call the first blue lyas and building lime, the other black lyas and
ground lime. They informed me that the building lime always lies
above the ground lime, and in a quarry in the parish of St. Decu-
man’s I saw a section where the upper strata were pointed out to
me by the workmen as the best building lime, and they find the
Strata become less adapted for that purpose the lower they go. I
found the middle beds slightly fetid, and the lowest more so and in-
creasing in thickness.

§ 36. The fossils which are very numerous in the lyas series in
most places, appear to be less abundant here. The cornu ammonis
is the most common, and I found it several times above 18 inches
in diameter. It frequently occurs in a flattened compressed state
with the beautiful iridescence of the nacre preserved ; a variety which
Mr, Townsend considers peculiar to the lyas of this coast.* The fol-
lowing are the few organic remains I had an opportunity of collecting:

Remains of a very finely striated Pecten or Lima.

* Character of Moses, p. 278. Mr. Townsend is mistaken in supposing that the
Pentacrinite is not found in the lyas of Watchet.

South-Western Part of Somersetshire. 369

Remains of a pentacrinite, resembling that which is found on
the banks of the Severn, near to Pyrton passage.

Fragment of a large compressed and strongly ribbed ammonite.

Slight remains and traces of some unknown pinnated vegetable
converted into coal. |

Remains of terebratula, much resembling T. lacunosa.

‘ Fragment of a large shell of the genus nautilus.

In several places the surface of the limestone strata is exposed for a
considerable way, shewing that in many instances they do not con-
sist of a continuous mass, but of an accumulation of columnar dis-
tinct concretions, resembling the Giant’s Causeway on the coast of
Antrim. These.concretions are distinctly separated from each other,
all their angles are rounded, and there is no regularity in the number
of their sides or their dimensions; in some of the strata the whole
surface of each concretion consists of that brown crust mentioned
above, enveloping a light blue nucleus. This structure of the lime-
stone makes it very easy to work, as it is only necessary to separate the
concretions with an iron bar. In this way a great many of the beds
near low water mark are worked, and the concretions are brought in
paniers on the backs of little horses and asses to the kilns on the top
of the cliff. I observed a similar structure in the red rock, but the
divisions were much smaller than in the limestone strata. In both
instances the appearance is very like that of a mass of dried clay or
starch, When the strata of limestone are not divided into those co-
lumnar concretions, they are generally separated into large irregular
shaped masses by joints perpendicular to the stratification, and in
many parts they are penetrated in every possible direction by con-
ternporaneous veins of calcareous spar crossing each other like net-
work. They seldom exceed a few inches in thickness, and are in
general much more slender ; the same vein which in the middle is an

VOL. III. 3A

370 Mr. Horner on the Geology of the

inch or two in thickness, gradually thins away at each extremity,
sometimes to a hair’s breadth, at other times shooting off like a
spreading root of delicate fibres. Very often a slender thread cuts
across a thick. vein, throwing it several inches out of its regular
course, affording a miniature representation of the disturbances in
the great veins of mining districts: These veins do not penetrate
the slate either above or below the stratum of limestone in which
they are contained: but there are other veins of calcareous spar
which cut through the strata, generally occasioning a dislocation,
and in many instances I observed the substance of the vein pene-
trating the adjoining strata in minute ramifications. It will be diffi-
cult to reconcile these appearances to any theory_of veins that has
yet been proposed; like other instances, which every country
affords, they tell us how little we yet know of the laws by which
the materials of our globe have been brought together into their
present arrangement.

§.38. The slate clay that is interposed between the strata of
limestone assumes different appearances. In some places itis grey,
in others brown, and in others nearly black: it is frequently bitu-
minous, having, when broken, a strong fetid smell. The strata
are divisible into lamin as thin as common pasteboard, splitting
with the greatest facility, and where it is washed by the sea it is
very soft and friable. It appears to contain the same fossils as the
limestone, and it is in this that the flattened ammonites are found ;
those in the limestone preserving their natural form, as far as ny
observations went. It frequently contains imbedded masses of a
limestone identical with that of the regular strata, of a lenticular
shape similar in form to the masses of clay-ironstone found in the
clay of the coal formations. ; These are frequently uniform in
structure throughout, sometimes they contain slender veins of cal-

South-Western Part: of Somersetshire. eye:

careous spar in their interior, running parallel to their shorter axis
but not reaching the surface, and they are sometimes divided into.
septa which are coated with calcareous spar and sulphate of strontian.
I was fortunate enough to break one of those masses which con-
tained this last substance most beautifully crystallized, quite equal
to many of the specimens brought from Sicily: the crystals are
perfectly transparent and of a pale blue tint. It is not confined to
these lenticular shaped masses, for J found it accompanying the cal-
careous spar of a vein in the quarries near Stringston. Thin strata
of a fibrous calcareous spar are frequently found between and‘ paé
rallel to the strata of slate clay and limestone. They are some
times about three inches thick, and the direction of the fibres 13
always perpendicular to the plane of the strata.

- § 39. About three ‘miles and a half from the mouth of thé
Parret and at the termination of the low marsh land, the lyas
strata first appéar, rising above the sand in a highly inclined po=
sition, and nearly covering the low shore between high and low
water mark.. They are very much covered with sea-weed, and
difficult of access from the very deep mud, but their general di-
rection may be traced running between east and west, and dipping
in some places to the north and in others to the south. After fol-
lowing this line of bearing a considerable way, they may be seen
sweeping round in a great curve, and becoming perpendicular in
their direction to the same strata not a furlong distant. They;
extend about a mile westward from their first rising, and
then entirely disappear opposite a tract of marsh land lying bez
tween two low hills along the shore for about half a mile: at the
western termination of this marsh they again appear in a highly
inclined position, and a little farther west the shore begins to be
bounded by -cliffs, which continue without interruption’ to Blue

2A Z

372 Mr. Horner on the Geology of the

Anchor, except at those places where the brooks at Little Stoke
and Donniford fall into the sea. From the place where the cliffs
begin to that part of the coast which is immediately below Perry
Court, they are entirely composed of the lyas strata, and that is
the most eastern point where the red rock appears in the cliff.

§ 40. In the whole course of this part of the shore the strata
hardly ever preserve a uniform bearing or dip for the space of a
quarter of a mile, but are liable to constant changes dipping in
every possible direction. It would be impossible, by any descrip-
tion of the particular instances of disturbance, to give an intelli-
gible representation of the extraordinary appearance of this coast
on walking over it at low water: I cannot convey a better idea of
it than by comparing it to the great waves of a sea suddenly con-
solidated. ‘These waves are now broken in many directions, and
exhibit various sections of their internal structure. That the con-
volutions took place when the rocks were in a plastic state is highly
probable, for the curve is complete, in many cases, without a
fracture. Besides these curvatures there are in many places along
the cliff, and particularly between Shurton Bars and Little Stokes
instances of those slips in the strata which are of such frequent
‘occurrence in the coal districts. Sometimes these slips are only of
a few inches, in general they are of a few feet, but they are
sometimes so great that in a cliff of 100 feet high there is a com-
plete change in the nature of the strata on each side of the slip ;
there being on one side of it a numerous alternation of limestone
and slate clay strata, and on the other only slate clay with a very
few thin beds of limestone. In general I found the line of the
slip filled by calcareous spar, sometimes only a few lines in breadth
and rarely exceeding a few inches, and in many instances as I have
already noticed, I found the matter of the vein penetrating the

South-Western Part of Somersetshire. 373

adjoining rock in slender ramifications. I found some slips where
nothing appeared but the line of separation.

§ 41. The lyas formation of this part of the district is hontided
on the south by a line commencing at Combwich, and passing
through Bondstone and Stringston Church to the point on the coast
where | have said the red rock begins, keeping a little to the north
of Putsham.* The road from Knighton to Shurton Bars crosses a
small valley, between two hills composed of lyas, and in the bottom
of this valley the red rock appears, accompanied as usual by its
grey beds. ‘This is one of the places where there is apparently a
distinct instance of the red rock alternating with the lyas ; for the
lyas on each side of the valley and the red rock in the bottom all
dip towards the same point. This however is not conclusive, for
the actual contact is not seen, and the same source of error which
I discovered in another place, and which | shall presently mention,
may exist here: the valley stretches in a north-westerly direction
and terminates on the shore near Little Stoke. I went to this
place expecting to see the alternation more distinctly in the cliff;
that however is wholly composed of lyas, but on proceeding along
the shore in the same direction I discovered a small portion of the
red rock appearing above the sand, with the lyas strata close to it
on one side, but whether they lie above or below the red rock it is
impossible to say, for they are, within the space of a few yards,
- both vertical and inclined, and dip to the north and to the south.

* Polden Hill, on the right bank of the Parret, the longitudinal direction of which
is the same as that of the hills on the left bank, is composed of lyas, and near Knoll inn
the red rock appears in the side of the road. Iam informed by my fricnd Mr, Poole,
f Enmore, that Pawlet Hill and Brent Knoll are also composed of lyas.

374 Mr. Horner on the Geology of the

I observed the red rock in the bottom of another valley between
two ridges of lyas, in the road from Benhole farm to Shurton,
and here the grey indurated beds contained blue carbonate of
copper. As might be expected from the disturbed state of the
stratification on the coast, the lyas strata inland rise into ridges ;
the longitudinal bearing of these is generally from east to west :
in the vallies between them patches of red soil often appear, which
are no doubt owing to the red rock being subjacent. ,

§ 42. The northern termination of the Quantock hills dee
scends with so rapid a slope to the sea that I expected to find a
section of the grauwacke series exposed in the cliff on the shore,
which in this place is above a hundred feet high: there is not
however the slightest appearance of them, the whole cliff being
composed of the red rock. Where the lyas and the red rock meet,
the stratification of both is, in general, much confused, although
at .a short distance from the junction they are seen in conformable
stratification. ‘There are some very distinct instances of regular
strata of lyas lying «fom regular strata of the red rock, but in all
those cases where, if the strata were continued without interrupticn,
the lyas would lie wzder the red rock, there is always so much dis-
turbance at the junction as to render it very doubtful whether the
lyas strata are not turned up or abut against it. The strata of red
rock near the junction with the lyas in this part of the cliff are

nearly horizontal or dip to the north at a very small angle, but in -

the western part of the bay they dip south-west, and are covered
by conformable strata of lyas; and in this place the grey beds of
the red rock are more numerous than in the eastern part of the
bay. The lyas strata continue to that part of the coast where
Donniford brook falls into the sea. Here there is a kind of delta;
formed of a great accumulation of gravel, consisting of pebbles of

“ad

South-Western Part of Somersetshire, 375

grauwacke and quartz similar to what is found in the surrounding
country. On crossing the brook the cliffs soon begin to rise again,
and the lyas strata appear at the bottom covered by about 12 feet of
this gravel, which becomes gradually thinner towards the west.
The lyas strata continue as far as the headland on the eastern side of
Watchet Harbour, and at the place of junction great confusion takes
place.
- § 43. It was in this place that walking across the line of bear-
ing of the strata at low water I discovered them in that position
which leads me to think that the appearances of the red rock alter-
nating with the lyas may be deceptions. Fig. 1. Pl. 24. is a ground
plan of this part of the coast, the dark line representing the cliffs,
and the faint lines the strata; aa being the limestone and 4 4 the
red rock. I found at A and B strata of lyas dipping towards the
same point, and conformably with the dip of the strata of red
rock at C. I therefore expected that as in going from A to B, I
should cross the prolongation of the strata of red rock from C,
although the ends of the strata were not much raised above the
sand, { might obtain distinct evidence of the red rock alternating
with the lyas: but instead of this I found the strata in the position
represented in fig..2. which is a vertical section in the line A B of
fig. 1. |
§ 44. The whole of the headland is composed of strata
of the red rock, dipping rapidly towards the north in the cliff;
but as they extend out to sea they undergo great changes, dip-
ping to every point of the compass and with every variety of
inclination. In some places they sweep round, forming a portion
of a great circle with the dip of the strata towards the centre, as
the lyas strata are seen to do in the eastern‘part of the coast. Heré
the grey parts of the red rock, which in general only appear a8

376 Mi. Horner on the Geology of the

patches, form regular strata alternating with the red, but at the
planes of junction graduating into each other.

Close by the town of Watchet, in the bottom of the bay where
the harbour is formed, the lyas strata appear to come from under
the red rock, but as usual the junction is obscured by great dis-
turbance. On the western side of the harbour the lyas appears for
a very short distance, and abuts against the red rock: at low water
the most varied curvatures and dislocations of the strata may be
observed. In the red rock eastward of Watchet there are some-
times slender veins of calcareous spar running across the strata,
and these, as in the lyas strata, are generally accompanied by a
slip.

In this part of the coast the red rock begins to assume a new
character, for it contains a large quantity of gypsum which does
not appear in it eastward of Watchet.

§ 45. The coast between Watchet and Blue Anchor is com-
posed of the red rock with grey patches, similar to that in the
eastern part of the district, of another variety of it containing gyp-
sum, of a blackish indurated clay traversed by gypsum, and of the
lyas strata. All these appear in the cliffs and on the shore at dif-
ferent intervals, but the great disturbances in the stratification have
thrown the whole into such confusion that I found it impossible
during my stay to come to any satisfactory conclusion as to their
relative positions. No description without the aid of plans and
sections would be intelligible, and these could only be made with
accuracy by a residence for some time on the spot. It would
amply repay the labour of any geologist who might undertake the
task, for the coast abounds with interesting phenomena, and he
would probably be able to determine decisively whether the red
rock does or does not alternate with the lyas strata) He would at

South-Western Part of Somersetshire. 377

least find abundant proof how very enigmatical the question as to
the relative position of strata frequently is; a question of the first
importance in geological inquiries.

§ 46. On leaving Watchet, the red rock is for a short distance
similar to what is found eastward, but veins of gypsum very soon
begin to appear, and they gradually increase in quantity. The
rock here is of a bright brick red colour, and very friable ; and is
traversed in every direction from the top to the bottom by pure
white veins of gypsum. Vast blocks of it have fallen down, and
are piled above each other and strewed along the shore; in those
that are within reach of the dashing of the waves the gypsum is
nearly washed out, giving them a very singular appearance. The
rock is not distinctly stratified, but the thickest veins of gypsum
are parallel to each other, and nearly horizontal : it contains as
usual the grey patches and stripes. The principal veins of gyp-
sum are of different thicknesses ; in some places they nearly equal
three feet, and the red rock between them is penetrated by smaller
veins branching off in all directions; but besides these there are
other veins which traverse the rest in every possible way. . There
are also detached masses of gypsum which are surrounded on all
sides by the red rock.

There are different varieties of the gypsum; it is in general
white, but it is in some places flesh coloured and bright red.
There are thick masses of 4 very pure compact alabaster fit for
many purposes in the arts, and there are several fibrous varieties.
In some places it is mixed with siliceous sand and small pieces of
quartz, and where these parts are washed by the sea, the gypsum
is dissolved, and leaves the quartzose parts projecting and very
often in beautiful forms. I did not find it in any case crystallized

VoL. 11. , 3B |

378 Mr. Horner on the Geology of the

in determinate forms, nor any appearance of its being accompanied
by rock salt.

§. 47. Near Blue Anchor the cliff is composed of a blackish
grey clay, containing thin beds of a slightly effervescent argillaceous
stone, and which appear to graduate insensibly into the clay.
These are penetrated in all directions by numerous veins of gyp-
sum, the thickest being parallel with the strata. The same varieties
are found here as in the part of the cliff near Watchet, though not
so abundantly; and although there is a very great difference in
the colour of the gypseous rock near Blue Anchor, and in the mode
of penetration of the gypsum, I have little doubt of its belonging
to the same formation as the red rock. ‘The strata are very much
disturbed, and in one place they form a complete arch dipping
south-west and north-east within the space of 50 yards.

All along the bottom of the cliffs where the gypsum is found
they are hollowed out by the waves dashing upon them, and
where the strata dip towards the sea the upper beds hang over a
considerable way in the form of a Chinese roof. Rills of water
flow over them in many places, and have worn deep channelsy
Dr. Maton, in his Tour through the Western Counties, when
describing these cliffs, says, that “ the gypsum may be seen con-
creting under our eyes.” A more attentive examination would
have satisfied him that there is only decay, and no production of
new matter on this coast. .

§48. The last appearance of the lyas strata on the shore is
about a quarter of a mile westward of Blue Anchor, where there
is a low cliff for a. short space, not rising above 12 feet. But even
in this limited extent the strata exhibit great disturbance. They
consist of a yellow clay, containing thin strata of limestone of a

cream colour, some slender veins of gypsum, and small, earthy,

South-Western Part of Somersetshire. 379

calcareous concretions. These rest upon strata of the fetid varieties,

and underneath these last there are other strata of yellow clay and -
cream coloured limestone, and in the lowest part of the series I

observed in the clay a thin bed of dark coloured limestone full of
shells. In this lower yellow clay there is no gypsum.

§ 49. The lyas strata do not extend far inland from the coast.
There are here, as in the country to the east, long ridges composed
of them, but the surface is very little broken. There are some
quarries in the parish of St. Decumans, others near the road from
High Bridge to Rydon, and upon the slope of the hill eastward of
Donniford.

§ 50. Westward of Minehead, in the lower part of the southern
face of North hill, near Venniford, there is found a small insulated
patch of the lyas strata. There is a quarry by the side of the road,
and it extends in a north-west direction upon the slope of the hill
as far as East Lynch, where also there are quarries. It appears to
be confined to a space of about half a mile in length, and one-third
ofa mile in breadth. ‘The strata in the quarry at Venniford dip at
an angle of about 30° a little to the west of north: those at East
Lynch are horizontal. The occurrence of this detached portion of
the lyas strata is very remarkable, being above six miles distant
from the last appearance of the lyas at Blue Anchor, and the high
ridge of Heyden Down intervenes, which is wholly composed of
the grauwacke series.

I should also notice that immediately below the quarries at East
Lynch, the red rock, with grey patches appears in the side of the
road. Thisis, I believe, the most western point where the lyas
strata are found in England.

§ 51. About three miles westward of the river Parret, there
occurs on the sea-shore one of the most remarkable features of

3B2

380 Mr. Horner on the Geology of the

this coast, viz. the remains of a forest considerably below the level
of the sea, and now only to be seen at low water.*

The first appearance of this submarine forest is opposite Stolford,
about a quarter of a mile eastward of the place where a small brook
runs into the sea. From this point to the mouth of the Parret there
is a flat shore, which at low water is covered with a deep and
almost fluid mud. The adjoining land is protected from the sea
by a high bank of pebbles, composed almost entirely of the lyas
limestone, and which increases in height near the place where the
forest begins. Here there are seen at intervals patches of various
dimensions raised six or eight inches above the sand, and upon
digging into these they are found to consist of a dark brown matter
resembling peat or decayed vegetable substances, mixed with a plant
in which the structure is entire, with twigs and small branches of
wood in a soft state, and containing here and there a few nuts.
This brown matter rests upon a light blue very stiff and unctuous
clay, and is of various thickness ; in general from a foot to eighteen
inches, but in one place I observed it two feet and a half without
coming to the blue clay. Trunks of trees of a very large size are
found at different intervals surrounded by the brown matter, and
with their roots diverging as they grow, and fixed in the blue clay.
The smaller twigs and branches in the brown matter, which look
like the roots of underwood, also penetrate the blue clay, and the
clay contains a great deal of that particular plant which appears the
least decayed in the brown matter. Besides the trunks there are
stems of great trees sunk in the brown matter and strewed about,
but without any uniformity of direction: some of these I found 20
feet long, and many of them had lateral branches attached to them.

* ‘This submarine forest was first pointed out to me by my friend Thomas Poole, Esq.
of Nether Stowey.

South-Western Part of Somersetshire. 381

In many places, but particularly nearest the blue clay, the brown
matter had a strong smell resembling that of bilge water. .
§ 52. In order to ascertain whether the species of any of the
plants contained in the brown matter could be made cut, I sent
specimens of it to my friend Mr. Brown of the Linnean Society,
whose eminent skill in botany is so well known, requesting him
to examine them. He informs me that the plant which was best
preserved was the only one upon which he could pronounce with
any degree of probability, the rest being too much decayed. It
resembles the common Sea Grasswrack, but the leaves are so much
broader that he considers it more probably the Zostera Oceanica of
Linnzus: it is worthy of remark, that Dr. Smith, in his Flora
Britannica, when speaking of this plant, says, “ Zostera Oceanica
Linnzi, sui generis planta, nostras nunquam oras attigit.”’

§ 53. There are several sorts of wood, but it is difficult to
say to what species they belong. Iwas accompanied in my exami-
naion of this forest by John Acland, Esq. of Fairfield, and some of
his friends, who seemed to agree very generally that some of the
trees were distinctly oak and yew. Of these, and particularly the
latter, the texture is still entire; there are others which are soft
and easily cut by the spade, but even these when allowed to dry
become very tough and hard. The trunks seldom appear more
than a foot above the ground, and they seem as if the stem had
been broken off. Some of them however are smooth, as if sawed
across, which has probably been the case, for a great deal of
the timber has been carried away by the country people; and I
was told by a farmer who had lived a great many years in the
neighbourhood, that he recollects when there were stems standing
erect above the height ef a man, with lateral branches extending
from them. This farmer some years ago ploughed up a part of

382 Mr. Horner on the Geology of the

the forest, and took away above forty cart-loads of the trees, part
of which he used as timber, and the rest-as fuel; but for the latter
purpose it was very unfit, on account of the offensive smell it
produces when burning. He shewed me a gate post, which he
said was one of the sub-marine trees; it had been put into the
ground 40 years before, and was quite entire: he had no doubt of
its being yew.

§ 54. From the place where the forest first appears it continues
westward about three quarters of a mile without interruption, and
it may be most advantageously examined opposite Ham Wall, a
barrier erected against the encroachments of the sea. From this
point the shore is occupied by the lyas strata for nearly two miles ;
when, near Shurton Bars, there is a great disturbance in the strati-
fication, and the rocks totally disappear on the shore for some way,
although they continue in the cliff to the height of 20 feet. Here,
about a quarter of a mile from high water mark, more remains of
the forest are found; and in this place I saw the greatest depth of
the brown matter and the largest tree. It was about three feet in
diameter, and from the concentric circles it was evidently of a
great age: Mr. Acland had no doubt of its being an oak. It was
of a dark brown colour, and had a greater degree of soundness
than most of the wood that is found. There is no appearance of
the forest westward of Shurton Bars, as far as I could discover,
nor indeed is it likely, for the coast from a little way beyond that
point is rocky, and the remains of the forest are only found in
those places where the curvature of the lyas strata has formed
hollow basins. Warner however, in his Topographical account of
Somersetshire, mentions some remains of trees on the shore be-
tween Dunster and Minehead. I carefully examined that part of
the coast without finding any thing of the kind, but they have

South-Western Part of Somersetshire. 383

perhaps been washed away since the time he observed them, for in
the place where the forest now exists it was formerly of much.
greater extent, and is evidently wearing away so rapidly by the
action of the tides, that it is probable not a trace of it may exist
some years hence. How far it extends out to sea it is impossible
to say, for from within half a mile of low water, the shore is
covered with mud.

§ 55. There is a very considerable resemblance between this
submarine forest, and that on the coast of Lincolnshire observed by
Sir Joseph Banks and Mr. Correa de Serra, and described by the
latter in the Philosophical Transactions for 1799. I did not how-
ever find that flattened appearance of the trees which he speaks of,
and the bark did not seem to be better preserved than the rest of the
tree. I could not leara that any similar substratum had been found
in the adjoining country, but it is stated by Mr. De Luc, that in
‘digging new channels for the rivers Brue and Axe, eastward of
Bridgwater, there was found at a great depth under the soil of the
marsh, a continuous bed of peat.

§ 56. it is hardly possible to describe this interesting pheno-
menon without offering some conjecture as to its cause. Before
any rational and well grounded theory could be formed, it would
be necessary to examine with great attention the district of low
land adjoining to the river Parret, and to collect all records of
sections that have been made in it. The explanation that most
readily occurs is that it has been caused by an encroachment of the
sea on the breaking down of some barrier. But the remarkable
disturbances that appear in the strata, the slips in these which must
have evidently taken place after the consolidation of the rock, and
the occurrence of the forest opposite that part of the coast where
there are perpendicular cliffs 20 feet high, appear to me to favour

384 Mr. Horner on the Geology of Somersetshire.

very strongly the supposition that the forest has been submerged
in consequence of a partial subsidence of the land.

I have confined myself in this paper almost entirely to a descrip-
tion of facts, without entering into any of the geological speculations
which they suggest. But as theory is the great end of all inquiries
of this nature, a Geological memoir may be considered incomplete
unless the facts are examined with the view of discovering what
legitimate deductions may be drawn from them. My examination
of this district was however so cursory as to render it impossible for
me to observe the facts with that patient and minute attention
which could alone entitle me to make any theoretical inferences
from them. Some of the most interesting theoretical views, the
recital of the facts alone will suggest. to every one accustomed to
reason on Geological phenomena, for there are probably few places
where more remarkable proofs are to be found of the great distur-
bances which have taken place in the strata since the time of their —
first deposition. ‘To those geologists who may hereafter examine
this district, I would recommend the singular accumulations of
conglomerate, described § § 21. 23. 25, and particularly the detached
hill of Tor Weston, and those near Tarr and Vellow, whether
there is any evidence of some powerful cause acting on the surface,
having left them in their present insulated position. ‘The apparent
alternation of the lyas strata with the red rock on the shore also
deserves an attentive examination, and there appears to me an ex-
cellent opportunity in this district of investigating the history of
that red rock about which so little is yet known, though occurring
to so great an extent throughout England.

X. Description of a Clinometer.

By tue Ricat Hon. Lorpv WEBB SEYMOUR, rF.rs. F.R-s.5. F.L.S.

MEMBER OF THE GEOLOGICAL SOCIETY.

[ Read May 20th, 1814.]

In every description of stratified rocks the importance of deter-
mining the position of the plane of stratification, by referring it to
some standard, is so obvious that to insist on it would be a needless
intrusion upon the time and attention of this Society. The object
of the present paper is to submit to the Society a description of an
instrument contrived for the above purpose, accompanied by draw-
ings, and to add an explanation of the method of using it. This
instrument has received the name of the Chinometer.

The Clinometer consists of two parts, the p/ate and the quadrant.
Plate 25, exhibits both lying horizontally, the quadrant in the
position in which it lies packed in its case. Plate 26 shews the
two parts put together, lying upon an inclined surface, and adjusted
for an observation to determine its position. In both plates every
part of the instrument is represented of the real size, and the
references in the description are made to both by the same letters.

The plate represented by A, is circular and of brass. On
the under surface, near the edge, it is thickened by a ring to give
it greater strength. It is supported by three feet aaa, placed at
equal distances just within the ring, and made of wood, with their
ends flat and broad, of a form somewhat oval, and having its length

VOL. 111. 3°

386 LorD WEBB SEYMOUR oz a Clinometer.

in the direction of the margin. Wood is preferred to metal for
the feet, as less likely to slip on a smooth surface; and they are
made broad at the end, to prevent the position of the plate and
the firmness of its rest from being too much affected by the minute
inequalities of a rough one. The flat ends of the feet are adjusted
to.a plane parallel to the upper surface of the plate; and the fibre
of the wood is set perpendicularly, in order to prevent any derange-
ment from the expansion and contraction of the wood attending
the changes of moisture. ‘On the upper surface near the edge, is
a circle divided into degrees, which are numbered from zero to 90°
through the four quarters successively in the same order; and it
is of no consequence whether this is done from-left to right, or
from right to left. In the center of the plate is a circular hole 4,
to receive an axis on the under side of the base of the quadrant.
For securing it, there is a bolt cc, which slides below, and is
worked by a catch d rising through an oval hole in the plate and
made flush with its surface.

B represents the quadrant, which has all its frame-work of brass.
‘GG is its base, which traverses upon the plate; at ¢ is the button
of the central axis, which is secured in the center of the plate by
the hollowed end of the bolt beneath, and at fis the clamp and:
milled-head screw, for fixing the quadrant to the edge of the plate
in any direction. At/ is a rectangular aperture, through which
the divisions of the plate are seen, and read off by an index on the
‘middie of the bevelled side of the aperture nearest to the central
axis. DD is the graduated arch, fixed firmly to the base, and at
right angles to the plane of its under surface. It is divided into
degrees, which are numbered from below. At 4 is the head of a
‘short axis passing through the center of the arch, and revolving
with the motion of the radial bar mm, which carries with it the

Lorp WEBB SEYMOUR on a Clinometer. 387

spirit level EE, and the compass 000. This axis is made to move
with a degree of friction sufficient to support the weight of the
radial bar in any position. ‘The level turns upon its axis by twa
pivots pf set in two small plates projecting from the extremities
of the radial bar, and through the same plates, immediately below
the level, passes a strong conical axis rv, to one end of which
the compass is fixed, and with which it revolves.

The compass-box has its bottom, as well as its top, made of
plate-glass, and each of the two pieces is set in a cylindrical rim of |
brass which forms its sides. ‘To the middle of this rim there is fixed,
on the inside, an annular brass plate, silvered and graduated in
the same manner both above and below. The divisions are of
two degrees. There are two zeros, one in each intersection of a
line passing through the center, and on both sides of each of them
the divisions are numbered alike, till they meet in two nineties, in
a line at right angles to the first. At g is a catch for working a
bolt sliding on the outside, which lifts the needle from its pivot in
the usual way, by the bent lever s. The needle has the north
pole marked on the under, as well as the upper, side, and also an
index line drawn from one end to the other.

In adjusting ,the different parts of the quadrant to each other
regard must be paid to the following circumstances ; that the axis
of the level may be parallel to the line from the center of the
quadrantal arch to the index on the radial bar; again, that when
the radial bar is home upon the base, the axis of the level may be
parallel to a line, in the plane of the base, from the center to the
index of the base, and that the index of the radial bar may at the
same time point to zero; also that the line of the two zeros in the
compass may be parallel to the axis of the level, at least, when the
plane of the compass is at right angles to that of the quadrantal arch.

3c 2

388 Lorp WEBB SEYMOUR on a Clinometer.

The clinometer may be used to determine the position of any
plane surface to which the plate can be applied, so as to admit of
observation with the quadrant. The upper surface of a rock is that
which presents itself most frequently, and the mode of observing
it may be thus described.

As the surface of a rock afforded by a strata-seam seldom ap-
proahes to a perfect plane, a part of it must be chosen, which
appears to give the mean, or average position of the stratification.
If the surface be smooth, the quadrant may be fixed upon the plate,
before the plate is set down upon the rock. If the surface be rough,
the plate must first be set down, and adjusted by the eye, till its
surface appears to coincide with the mean position of the strati-
fication ; the quadrant is then to be fixed on. In fixing the quad-
rant upon the plate, the clamp should be thrust upon the edge,
before the button of the central axis is inserted. No regard need
be paid to the situation of the zeros of the plate.

The radial bar must be set home upon the base; and while one
hand presses the plate firm against the rock, the other must be
applied to the head of the screw g, and bring the quadrant round
till the level, properly adjusted by turning it upon its axis, is ho-
rizontal. Its axis will now be parallel to the line of stretch, that
is, to a line determined by the intersection of the plane of the
stratification with the plane of the horizon. The division on the
plate, to which the index of the base points, is then to be noted,
and the quadrant carried upwards to the same division in the next
quarter of the plate; when it will have described an arch of 90°,
and of course be now in a vertical plane, at right angles both to
the plane of the stratification and to the plane of the horizon.
After clamping the quadrant to the plate in this position by turn-
ing the screw g, the hand is shifted to the compass in order to

Lorp WeEsB SEYMOUR oz a Clinometer. 389

raise the radial bar till the level, duly adjusted on its axis, marks
the horizontal line. When this has been done, and the needle
has settled, the degrees on the compass are to be read off between
the zero farthest from the quadrant, and the point of the needle
néarest to that zero. This gives the magnetical bearing of the
plane of the dip, that is, of a plane at right angles to the line of
stretch on that side on which the plane of the stratification sinks
below the plane of the horizon.. The instrument may then be
lifted from the rock, and the angle of the dip read off upon the
quadrantal arch, being the angle which the plane of the stratification
makes with the plane of the horizon. ‘The bearing of the line of
stretch is deduced from the bearing of the plane of the dip, as
being at right angles to it. A correction for the magnetical va~-
riation gives the true position.

The roof of a cavern or of a mine, and sometimes the over-
hanging of a rock, may present an under surface for observation ;
but the instrument can scarcely be employed without an assistant
to hold the plate firmly pressed upwards.

For an observation of this kind, the level and the compass-box
must be inverted upon their axis, so as to have their faces turned
towards the plate. The level is to be brought to the horizontal
line as in the former case; but the quadrant must then be carried
downwards through an arch of 90° and clamped by the screw.
The radial bar is also to be drawn down till the level becomes ho-
rizontal. The magnetical bearing is read off upon the under side
of the graduated plate in the compass.

The origin of the instrument is as follows:—A few years ago
Mr. Grifiths, of Dublin, when making a mineralogical tour in
the Highlands of Scotland, employed for measuring the dip of
strata an instrument, which differed little from a common road

390 Lorp WeBB SEYMOUR on a Clinometer.

level, except in the size of the graduated arch, while he observed
the bearing at the same time by a compass carried separately. Mr.
Jardine oi Edinburgh made the important improvement of having
the compass mounted upon the radial bar, and placed it between
the center and the graduated arch. Soon afterwards I had an in-
strument made in imitation of this, but, in order to reduce the radius
of the arch, I had the compass fixed at the end of the radial bar.
There was a difficulty in applying the base of this instrument to the
surface of a rock, so as to place it with precision in the line of great-
est depression, and the endeavour to remedy it led me to the idea of
the plate. Two other clinometers were successively made for me
upon this plan, with such further improvements as experience
gave rise to; and the last was adapted for observation upon an
under surface, upon the suggestion of Mr. Jardine. ‘This last
contained all the principles of the instrument in its present state,
and was given as a model to Mr. Troughton, who, in making that
which has now been described, introduced a more simple con-
struction of the radial bar, and shewed that ingenuity which dis-
tinguishes every object of his labours, by other alterations con-
ducive to strength and lightness as well as to greater ease and ac-
curacy of observation.

The chief objection to the instrument in its present form, is
the weight of the plate. But it is necessary that it should have a
certain diameter, in order to admit of its adjustment by the eye to
the mean plane of the stratification, and it must have a thickness
sufficient to prevent it from bending much under the pressure re-
quired to hold it against a steep surface. No substance occurred
besides a metal, that was not liable to some objection, particularly
that of warping.

The clinometer may be employed for other purposes, besides

. Lorp WEBB SEYMOUR on a Clinometer. 391

that of determining the position of strata. The contents of a
solid contained by planes may be determined from the dimensions
and relative positions of these planes, and for ascertaining the
latter the clinometer may be used, where great accuracy is not
wanted. Mr. Jardine has used it in gauging a pond, of which
the sides were pretty regular slopes. By having the end of the
button of the central axis and the bottom of the milled head
screw so adjusted by grinding, that they may be in a plane pa-
rallel to that of the base of the quadrant, he has made the qua-
drant useful in supplying the place of a common spirit level upon

many occasio ns.*

* The instrument may be had from Mr. Cary, Optician, in the Strand.

15

XI. 4 Sketch of the Geology of the Lincolnshire Wolds.
By Mr. EDWARD BOGG, Land Surveyor.

‘Communicated by H. Warsurton, Esq. Secretary of the Geological Society.

{ Read January 19th, 1816.]

BEING resident in a district which has been but little noticed
as to its geological structure, I have drawn up the following re-
marks on its stratification ; and though omissions may occur, yet I
trust that an account of the Wolds of Lincolnshire and the adjacent
country, may not prove uninteresting to the members of the
Geological Society.

In conformity to the request of the Rev. Mr. Buckland, Professor
of Mineralogy in the University of Oxford, I have endeavoured to
trace on the annexed map, PI. 24. fig. 4. the denudations or bassets
of the chalk, the oolite limestone, and the sand strata, together
with the alluvial earth and hills of the same formation, with as
much accuracy as my personal knowledge and the nature of the
country will admit. I have also added a sketch of a section,
Pl. 24. fig. 3. on the same scale as the map with respect to hori-
zontal distance (the elevation being merely imaginary) intended to
elucidate the order of the stratification.

Mt. Boca on the Wolds of Lincolnshire. 393

Tt is obvious that as the general dip of the strata of this district
forms but a very small angle with the horizon, the superficial ex+
tent of the different beds occupies a greater stretch of country than
from their thicknesses might at first be apprehended : in the section
indeed, these measures are represented at considerable angles, yet
by keeping the circumstance above mentioned in view, I hope-it
will be found to answer the purpose for which it is intended.

The marshes betwixt Louth and the sea, No. 1 of the section,
consist principally of unstratified clay, with mixtures of sand and
various marine depositions, which tend to prove that this mass of
earth has been left by the ocean. A further confirmation of this
may be derived from tracing the sites of the different old banks
which once evidently formed the boundaries of the sea, which has
now retired a considerable distance from them.

Proceeding westward we come to the basset of the chalk No. 2,
being the highest stratum in this district. It forms the principal
part of the Wold hills, extending in this section from Louth to the
highest hills in Donington, a distance of about six miles: this stratum
dips under the marshes ; for on boring in them for water, the chalk
is always found. On arriving at this, the workmen never fail to
come at springs, and generally of sufficient strength to flow up
higher than the surface, thereby Justifying the conclusion that this
bed is the uninterrupted continuation of the same chalk, the rough
elevated basset of which forms the Wolds ; and by the pressure of
the water in which, the fountain springs obtained by boring in the
marshes, are at once accounted fos

In the neighbourhood of Tetney, a village situated on the coast,
are natural outlets of water called blow-wells; their depths have
never yet been ascertained, but we cannot entertain a doubt of
their communicating with the chalk. These wells overflow with a
VoL. Wil. 3D

394 Mr. Boce on the Wolds of Lincolnshire.

greater flux at the time of high water, and particularly at spring
tides; showing that the water in the chalk communicates with the
sea, a circumstance which would lead to a supposition that the sea
rests immediately on the chalk at a certain depth: if so, we might
possibly expect that the agitation of the water would frequently
throw up chalk on the coast, which I have never yet observed. |

The chalk consists of two colours, red and white, each lying in
regular strata, the red being generally undermost: in the white,
seams of flint are frequently met with from two to six inches thick.

The stratum, No. 3, immediately below the chalk, is a coarse
brown pebbly sand without organic remains, consisting of quartz
and oxyd of iron. This bed is, I apprehend, of irregular thick-
ness; I suppose it may vary from six to ten yards, but its appear-
ance at its basseting is very uncertain; for, being of a very loose
texture and the chalk which reposes upon it being of a more
compact nature, it is evident that when these parts were exposed
to the action of water, the sand being less capable of resisting
the washing of that element than the chalk, this latter would be
left in many instances forming projecting cliffs; which time, and
the well known action of the atmosphere, would crumble down
over the sand, and form those declivities which now in such variety
are exhibited to our view.

The next bed, No. 4, contains in nearly equal proportions oolite
limestone and calcareous clay of a lightish grey color. In certain
parts of this bed the clay divides the seams of stone into regular
strata; in others the stone is found to occur in the clay in large
detached pieces. This bed never extends to any great distance
beyond the chalk, forming in general a sort of step at the foot of
its basset. Lumps of pyrites are frequently met with in the lime-
stone. The thickness of the entire bed of stone and clay may be

Mr. Bows on the Wolds of Lincolnshire. 395

about twelve or fourteen yards: it forms a close measure, and I.
apprehend supports the water collected by the open strata which
repose upon it, for water is always found either in the chalk or in
the ferruginous sand immediately below it, the well sinkers never
having occasion in this district to go deeper.

, The next in order, No. 5 of the section, is a stratum of grains
of quartz, which for the most part are conglomerated into sand-
stone of different shades of colour, from a dark brown to a light
grey, while in some places loose sand predominates. Marine shells
are found in this stone, each species. appearing to be restricted to
certain laminz of the stratum: in the sandy portions I have never
observed any organic remains. I consider this measure as con-
siderably thicker than either of the two incumbent ones, Nos.
3 and 4.

I now come to the lowest visible stratum in our district, No. 6
of the section, which I term the shale stratum. It generally makes
its appearance in valleys, and its thickness I cannot estimate, for
I do not know where it exhibits any thing like a denundated ters
mination. My brother (Mr. Thomas Bogg of Louth,) and myself
have bored in this stratum to the depth of a hundred yards near
the village of Donington, on the west side of the river Bain, and
found it to consist of the following varieties.

3n2

396

BON AG DB wWNW He

10

Mr. Bocce on the Wolds of Lincolnshire.

Yds.|Feet
A clay soil ...... «(aha Ahh e PAPA as chaste othe OR re Rs oa
Dank GOlOURER CGY . > git. voy tes eee) oi ames = 6 es ate Mews 3] —
Soft grey slate with marine impressious ............ sremieie “—] 1
Dinelarediscems stomeee = as. ee. Bee tdni peices —|—
PATE CONDHECN C1 oni als, 0 aye ale shiis. pants Aetjan mumrapeh iors Sale ~l}—
Soft grey slate same as No. 3........ 606. ara [otto by. aserg £2 +6 —| 1
Laminated clay slightly indurated............ aioe int ERE Fiber?
Soft grey slate slightly infammable............6.. 040.2086. 1 2
Same as No. 8. but darker coloured ............6 gees coe ra 72
Indurated clay with white marine organic remains.. ......... 12 \esd
Same as the last but harder and blacker ............-....5.-+> 2 1
Dark coloured bituminous inflammable schist...........-..6. 2 —
A dark blue coloured jronstone .. 4.2 ...,- oie eccle aelcwise tates betas

—

Laminated indurated clay with white marine orgauic remains... | 1
Same as No. 14. but harder, with marine impressions consisting

Be Ram! Fate Eectases ot! eee ol BE

tele is|ey

alladS=|1 ws

tS) eal) Lenl

PL LOI SCARY OTM er oh. ave te yraley » € ohs SPURNS Sites «CME ats 3 1
Dark, blue jargillaceons;stone,; =<. (2). bi. J. sm bfeleT}de)> debe Je —|—
liard indurated, laminated clay ; with impressions consisting of

thimdesfy(pyrues ). TSDIGCR 22. ... ARCS. AWE SH 6 | —
Laminated bituminous schist, with white marine organic remains

atdintaminale tt . 207. 2544.29. Aad, ARRAY, 2 somal
Darle blue wontons. os ck. Pe Pete iss Cokie eee. —|—
Laminated bituminous schist, same as No. 18 .........2-0005 ssa tz
Dark Dine irenstone . 2: secs now ey -ebel arse tpeeeres|- are e re —|—
Laminated bituminous schist, same as No’s. 18 & 20.......... 6|—
Dark indurated clay, with some white marine organic remains. . 1 | —
Laminated bituminous schist, same as No’s. 18, 20 & 22...... 3 | —
Dark indurated: clay, same)as) No.023). 0). ../202. ob dk 2); 2
Laminated bituminous schist, same as No’s. 18, 20, 22 & 24... 1 1
Dark dry indurated clay, same as No’s. 23 & 25, intermixed with

thin seams of laminated bituminous schist...... PMD cll 10 | —
EONUEN re. A eae ee ote «Mr ans « Beni id Sat SES AigutierTe alot —}|—
Brown jamiuoted Seinst, tka stad, a che ony - proejtucras > els —}|—
Hardstone bind or argillaceous stone... ..... eee cesses eens —]| 2
Nard laminated, bituminous schist ............+-50.. eit tl = 1
ERgrActORe DINO RAMEN TBR OO. eels hc cases eee ie mae —| 2
Hard laminated bituminous inflammable schist............... —| 2
intammable:slaty Din) 2... cmrcwi ysis seer ee meee ite 1{—
Hard laminated bituminous schist, very inflammable.......... 1} —
Hard dark blue bind interlaid with thin strata of bituminous schist | 4] 1
Very tullammable schists: ).0. a's en dateaie« ss 00 dao se eben ells s —|—
Hard dark blue bind, same as No. 36............. A Ri AP ace 1| —
Yi FMEA AGN Se OOOO OOo. . - (OCIS ISAO son ad sce — | 1
NAN eas LN OsysOsp UC NOL SO! HalGlesctsye) atte cleye/cllalels 1 scl ein!) </a/es —| 1
Hard dark blue bind, same as No’s. 36 & 38 ........2...05- foal?

in which the boring was discontinued. a ee ee

[ al eosnw ene w | © Sto 29 oo

Mr. Boce on the Wolds of Lincolnshire. 39T :

Every:-variety of this stratum agrees in the two following proper-"
ties, the presence of calcareous matter, which is manifested by a.
brisk effervescence: when any part of it is submitted to the action of
acids; and secondly, a more or less abundant mixture of pyrites ;
all the bituminous slates when exposed to the action of fire burn.
with a very strong offensive smell ; but those found below the depth’
of eighty yards were not so disagreeable, in that respect, as those
which were higher in the stratum. Varieties 33 and 35 were.
remarkable for their inflammability, and burned witha thick bitu-
minous flame, appearing nearly equal in this respect to common
coal; but after the bitumen was exhausted, the remainder was left
undiminished in size. The organic remains which I have observed
in this stratum as its general characteristics, are impressions of the
cornua ammonis and some small bivalve shells.

The last division which I shall here notice, No. 7 of the Section,
represents the’ alluvial collection of earth which appears to consist
almost entirely of the spoils of the neighbouring strata. When
these parts were deluged by water, the current evidently appears to
have set in from east to west ; for this collection of matter is found
to consist principally of a mixture of the different strata which occur
to, the east of it in a state of decomposition; and in this mixture
which is by no means regular, detached pieces of the beds before
alluded to are found unaltered. Of these beds the chalk would °
expose the greatest surface to the erosion of the water, and next to
this the shale would be most extensively acted on; accordingly we
find that the alluvial deposition is composed of white marle and of
blue, the former of which being of the least specific gravity, has
overspread the higher parts and the summits of the hills, while the
lower parts and the vallies are occupied chiefly by the latter. In
the blue marle I have frequently found a variety of fossil shells,

398 Mr. Boce on the Wolds of Lincolushire.

and fossil wood, &c. together with specimens of all the earths and
stones, more or less worn by trituration, which the district pro-
duces ; I apprehend also that fragments of strata are deposited here
which have come from a great depth, for pieces of very pure
laminated coal are frequently to be met with which burn with a
very bright light, and leave but a small residue of ash. Other
pieces of jetty coal often occur breaking with a conchoidal fracture,
but these agree in every respect with a thin stratum of this fossil
which has been discovered at superficial depths in some situations
in the shale stratum.

On the Lincolnshire coast, a considerable quantity of coal agree-
ing in properties and appearance with the latter of these varieties,
is washed up by the sea, and is often collected by the poorer sort
of the inhabitants for fuel; and along with this: particular species
of coal, slates similar to those in the shale measures often occur, a
fact which gives us reason to suppose that the seam of coal from
which these specimens have been displaced extends under the
incumbent strata already noticed, into the sea, where the coal seam
is denudated and from whence these washings proceed.

As the discovery of coal would: be a circumstance of much
importance to this country; it might’ be worthwhile to have it
ascertained whether a seam of this jetty coal (called by the country’
people grome/) does not exist in sufficient thickness, and at such a
depth, as would render it worth the miner’s pursuit; the expense
of the boring requisite for this purpose might be defrayed by a
subscription among. the different land proprietors in the district.

, XIt. On the Tremolite of Cornwall.

’ By tue Rev. W. GREGOR,

HONORARY MEMBER OF THE GEOLOGICAL SOCIETY.

[Read 2ist May, 1813. ]

T po not know whether some observations upon a fossil of the
Tremolite species, which I discovered some time since in the county
of Cornwall, may be worthy the attention of the Geological Society.
I was induced to record them for the following reasons. I was not
aware that tremolite had ever been noticed before in our western
counties, ‘The existence of it in the particular rock which I should
conceive would be classed amongst the serpentines, is not, as I am
informed, an usual occurrence: and above all, I wish to draw
the attention of experienced and scientific geologists to the district
where this fossil was found.

I met with it nearly on the summit of a hill, in a rock which
breaks forth in masses forming an irregular and picturesque ridge
called Clicker-tor. It is situated about three miles from the town of
Liskeard, very near to the great road which leads to Plymouth.
This ridge of rock is at a considerable elevation extending in a
direction from east to west, and (if I may venture to judge by the
eye) for upwards of a quarter of a mile in length. It forms a very

400 Rev. W. Grecor on the Tremolite of Cornwall,

striking feature in the neighbouring country. Blocks of the same
species of rock are scattered about in different parts of the hill and
in its vicinity.

‘This rock is of dark bottle green colour. All the specimens of it
do not possess an uniform degree of hardness: they vary also in
respect of fracture. The harder species frequently assumes that
wavy and polished exterior surface which characterizes the magne-
sian stones. It is sufficiently hard to scratch glass. It has an un-:
even and sharp edged or splintery fracture, which exhibits no
lustre. Upon examination of its surface with a pocket microscope,
it appears to consist of a very fine-grained uncrystallized substance
of a blackish green colour, interspersed with thin laminze of pre-
cious serpentine of a green colour. The rock of the softer species
seems to be composed of these two substances also. It has a few.
small greyish white specks scattered over it: these are occasioned
by some softer substance imbedded in it, I am inclined to think
that this substance is compact tremolite. The softer species of
rock may be scratched with the nail. It has an uneven fracture,
inclining to earthy. ‘This rock abounds with iron, insomuch that
the magnet is enabled to attract very small particles of it. It re-
sists a very strong flame of the blowpipe without being fused. ‘The
fine edges however of the harder species seem to yield a little to
its action.

In the side of the hill, below the ridge of rock, a quarry is
opened for the purpose of supplying the neighbouring road with
stones. Here the rock is laid bare in large® masses. It is accom-
panied in some places with asbest, and also with a fine white
earth, which appears from the filaments which are mixed with it,
to consist of asbest broken down in a state of partial decomposi-

tion.

Rev. Mr. GREGOR on the Tremolite of Cornwall. 401

Between the blocks which constitute the great mass of rock,
a compact substance of a greyish white colour, consisting of an-
assemblage of crystalline spicule diverging from centres, is found.
The same compact fossil occurs in the body of the rock, where
there has been no rent. This I found to be compact tremolite,
This substance assumes also another appearance of distinct and
separate crystallization. - Crystals of it occur in the fissures of the
rock, in a state of promiscuous and thick aggregation. They are
about three-fourths of an inch in length, at the longest ; and consist
of thin, tabular, rectangular prisms, the angles of which are, for
the most part, rounded off, so that the section of the prism appears
to approach to a long ellipse. Some of these crystals possess a
vitreous lustre, and are semitransparent. In general their surface
is dull, as if from the effect of weathering, and they are of a
brownish ash colour resembling axinite.

Before the strong flame of the blowpipe, a fragment of a crystal
melts into a greyish enamel. At the temperature 69. Fahr. I found
the specific gravity of these crystals to be 3.20.

I shall not trespass upon the time of the Society by recording the
minute detail of chemical’ experiments. I shall simply state the
mode of analysis which I pursued, and the final result of it, so that
I may furnish others with the means of judging whether I am war-
ranted in calling this mineral substance a tremolite. ‘The propor-
tions of the several constituent parts of this fossil are given accord-
ing to an average taken from 100 grains of the distinct crystals.

Acids produce very little effect upon the powdered crystals. No
effervescence was produced to indicate the presence of the carbonic
acid ; neither could I detect any other acid as a constituent ingredi-
ent, by means of fusion with pure carbonat of potash, neutralizing

WOL. Il: SE

402 Rev. Mr. GREGOR on the Tremolite of Cornwall.

the alkali by pure nitric acid, and subjecting the solution to the
ordinary tests.

Fifty grains treated in the usual way, with nitrat of barytes, &c.
furnished an alkaline salt, which when united with sulphuric acid,
assumed the figure of sulphat of soda by crystallization. But the
quantity of this salt was too small to admit of being weighed.

One hundred grains exposed to a red heat for a quarter of an
hour, were diminished in weight one grain. Pure alkalies do not
effect the decomposition of this mineral so easily as they do in the
state of carbonats. .

One hundred grains were mixed and fused with 400 grains of
dried carbonat of soda, ina platina crucible. Treated with mu-
riatic acid spongy flocks of siliceous earth subsided. Ammonia
precipitated from the decanted fluid a gelatinous matter of a reddish
brown, which was sufficiently edulcorated; and after ignition, was
treated with muriatic acid, which left a small portion of silica un-
dissolved. Sulphuric acid separated some gypsum. The contents
of the solution were now thrown down by means of an alcoholic
solution of potash, and the brown precipitated matter was boiled
with a superabundant quantity of the precipitant. The clear alka-
line fluid was treated with muriat of ammonia, which separated
some alumina, but in a quantity too minute for collection. Though
this circumstance occurred twice, I am disposed to think that the
‘presence of alumina should be considered as an accidental intrusion.
The brown precipitated matter consisted of oxide of iron with a
trace of manganese. The first solution from which ammonia could
precipitate nothing further, was assayed with carbonat of soda,
which separated a white matter, which was-increased by boiling the
fluid, even to dryness. It consisted of carbonat of lime and mag-

Rev. Mr. Grecor on the Tremolite of Cornwall. 403

nesia. The lime was converted, by means of sulphuric acid, into
gypsum, and thus severed from its associate.

The relative proportions of the ingredients are as follows.

Silica - - » 62.2
Lime ~ - 14.1
’ Magnesia - 12.9
Oxide of Iron. - 5.9

Water - - 1.
Of Manganese and Soda, [—

atrace - - - = (

loss. -).= ory mey dD

XIN. Some Observations on the Salt Mines of Cardona, made during
a Tour in Spain, in the Summer of 1814.

By THOMAS STEWART TRAILL, M.D.

MEMBER OF THE GEOLOGICAL SOCIETY.
[Read November 3d, 1815. }

Turse celebrated mines occupy the head of a small valley in the
immediate vicinity of Cardona, a town in the province of Catalonia.

This valley extends about half a mile in length, from the river
Cardonero to the mines, in a direction from east-south-east to west-
north-west. Its north-western side is bounded by a very steep and
lofty ridge, the summit of which is crowned by the town and castle
of Cardona. The opposite boundary is somewhat less elevated ; but
both sides are considerably higher than the upper surface of the
fossil salt. On entering this valley, the attention is arrested by bold
cliffs of a greyish white colour, which are soon discovered to:consist
of one vast mass of salt. The sides and bottom of the valley are
composed of reddish brown clay, forming a thick bed, from which
here and there large imbedded masses of rock salt project in the
manner of more ordinary rocks; especially along the winding ascent
which leads up to the town of Cardona. The summits of the ridges:
which bound the valley on each side, are formed of a yellowish
grey sandstone of a coarse texture, and containing many scales of
grey mica.

~

Dr. TRAILL on the Salt Mines of Cardona. 405

The great body of the salt forms a rugged precipice, which is
reckoned between 400 and 500 feet in height at the upper extremity
of the valley, and is covered by a thick bed of the clay above
mentioned.

The precipitous form is partly owing to the manner in which the
mine has been wrought for a series of ages. There is no excavation ;
but the salt has been procured by working down perpendicularly as
in an open quarry. The lowest part of the present works has a
solid floor of pure salt which is not above the level of the bottom
of the valley where no salt is found; but the real depth of the bed
of salt has never yet been ascertained. ‘The upper surface of the
salt is not level; but appears irregularly elevated, according to the
general outline of the hill in which it occurs.

The salt has been usually represented as forming an entire moun-
tain: but though it here appears supplying the place of common
rock, yet from its being confined to this valley, and not attaining so
high a level as the surrounding hills, it would seem more correct to
consider it as a mass or bed of salt filling up a valley, than as con-
stituting a mountain, which according to some authors* is a league
in circumference. ‘These dimensions could only be obtained by
considering the neighbouring heights as formed of this mineral; a
supposition not countenanced by my personal observation, nor by
the best information which I could collect on the spot.

The surfaces of the salt precipice which have been long exposed
‘to the weather are not smooth, but cut into innumerable shallow
channels, running in a tortuous manner, and divided from each other
by thin edges, often so sharp as to cut the hands like broken glass.

* Introduccion 4 la Historia Natural y a la Geografia Fisica de Espana, por Don
Guillermo Bowles.—Madrid, 1775.— Dillon, who translates him. Laborde, Itineraire
descriptif, &c. .

406 Dr. TRAILL on the Salt Mines of Cardona,

The channelled surface is evidently produced by the action of the
winter rains, which have given the whole a striking resemblance to
the surface of a mass of ice, which had been partially thawed and
again frozen.

“The general colour of the exposed surface is greyish white, with
here and there a tinge of pale reddish brown, from the colouring
matter of the superincumbent bed of clay. Towards the extremities
of the mass of salt, extremely thin layers of a pure and plastic clay.
are insinuated between layers of salt, so as to give it the waved
delineations which often occur in some species of calcsinter. The
general mass of salt is however of the greatest purity ; and in order
to be converted into snow white culinary salt requires no other
process but grinding. The greyish hue of the external surface is.
owing to the rain penetrating a portion of the salt, and by diminish-
ing its opacity, depriving it of the whiteness which the fresh fracture
generally presents. At the period of my visit the surface of this.
immense mass was perfectly dry, and in some places, where water
had most recently flowed, was covered with a snow white efflorescence:
This circumstance, as well as the sharpness of the edges above
mentioned, shew the little hygrometric water in the atmosphere of
that country, and the general purity of the salt from earthy muriates.

The fracture of the salt is highly crystalline, and usually exhibits
large granular distinct concretions, which give it sometimes the
appearance of a breccia, or of containing imbedded crystals,

A perennial brine spring flows at the foot of the great precipice,
and affords a strong proof of the little effect of water on this very
compact salt. The aperture through which the stream has issued
for many years, is not wider externally than two feet, and suddenly
contracts to a few inches; while the channel worn in a solid floor
of salt, through which the stream has long flowed, is not a foot in

Dr. TRAILL on the Salt Mines of Cardona, 407

depth. ‘This is partly to be ascribed to the water being saturated
with salt; but, during the rainy season, the stream is much aug-
mented, and thus cannot be supposed so highly charged with saline
_matter. Notwithstanding this, neither the solvent nor mechanical
_ effects of the spring seem to have much effect on the fossil salt of
Cardona. The waters of this spring flow into the Cardonero,
leaving in the valley a thick scaly crust of salt, resembling the ice
formed around our brooks in similar situations, During the rainy
season, it is asserted that the stream carries down such quantities
of salt into the Cardonero as to kill the fish in that river. This
assertion rests upon the authority-of Bowles, an able naturalist ;
- but he undoubtedly was led into error when he asserted, that the
waters of the Cardonero at some leagues below the mines yield no
trace of salt: from which he inferred, that salt. may, dy motion, be
converted into earthy matter. At Manresa, which is about twenty
miles below*Cardona, I tested the water of the Cardonero by nitrate
of silver, which indicated the presence of an unusually large portion
of mutiate of soda. The taste of the brine spring at Cardona is
intensely saline ; and the hand immersed in it, on being exposed to
the air, is instantly covered with a film of salt, The salt rock near
its source is most elegantly veined with delicate waved delineations
of an ochre yellow colour. .

The clay which covers the bed ‘ salt at Cardona and forms pe
sides of the valley, exactly resembles the clay found in the salt
district of Cheshire, having when dty some resemblance to shale
but becoming plastic when moistened. It is remarkably pure, and
free from intermixture except of salt, large masses of which. are
eccasionally imbedded in it.

408 Dr. TRAILL on the Salt Mines of Cardona.

No fibrous salt was to be observed at Cardona; nor did I discover
the slightest trace of gypsum in that neighbourhood; a remark
which was also made by Bowles. On the soil near the town, @
small quantity of a saline efflorescence was however observed, which
had the taste of sulphate of soda; but the loss of the specimen I
collected, has prevented a more accurate investigation of its pro-
perties. . ,

The salt mine of Cardona is wrought like an open quarry with
pickaxes and wedges, by which the mineral is raised in consider-
able tabular masses. The part at present wrought presents an
extensive horizontal floor of pure rock salt; the level of which is a
little lower than the foot of the great salt precipice.. An enormous
mass of the same mineral lies between this precipice and the present
mine, the removal of which will, in time, render the appearance of
this interesting spot still more magnificent; for then the vast front
of the rock salt bed will at once strike the eye from the lowest part
of the mine.

Like every other public work in Spain, the mines of Cardona
are in a languid state from the effects of the late war which has
desolated the peninsula, Only two labourers are at present em-
ployed in quarrying the salt, and in wheeling it to the receiving
house. Over these, eight overseers are appointed, who do duty in
rotation; and ten centinels are continually stationed around the
mine to defend it from the depredations of the peasantry. Several
clerks are employed in an office built at the entrance to the mine,
and the whole is under the direction of an Jutendente or Inspector,
who wears the uniform of an officer in the Spanish army; for the
mine is the property of the crown, and is most rigidly guarded.
Notwithstanding the rigour with which depredators are pun-
ished, the peasantry frequently attempt to deceive the vigilance

Dr. TRAILL on the Salt Mines of Cardona. 409

of the guardians of the mine. When detected, the usual punish-
ment for a peasant is, even on the first offence, two or three years
labour among malefactors in some of the public works in the
province. A soldier is however less severely punished when he
commits a similar transgression ; he is generally sentenced to a few
days solitary confinement in a dungeon of the castle. On asking
an overseer the reason of this disproportion in the punishment of
different offenders, he replied, that the soldier’s poverty was sup-
posed to extenuate his crime, while the peasant of Catalonia en-
joyed comparative wealth, and could afford to purchase salt for the
consumption of his family.

Such is the boldness of the smugglers and the jealousy of the
government, that it is dangerous to visit the mines without formal
leave from the Intendente; as the centinels have orders to fire on
any one seen loitering about them.

The workmen here receive considerable wages, and are all free
labourers ; each man receives daily twelve reals vellon, which at the
rate of exchange last year equals three shillings sterling: lads are
paid at the rate of eight reals, or two shillings; and boys receive
six reals, or one shilling and sixpence.* The hours for work are
from six in the morning to seven in the evening (in summer) ; with
the ‘intervals of half an hour, between 8 and 9 o’clock, A.M. for
breakfast, and two hours, from twelve to two, for dinner, and its
usual sequel in Spain, the svesta.

The produce of the mines is pulverized by grinding it in mills,
on the exact construction of our common water mills. This ope-

* This may be considered as liberal wages where the necessaries of life, with the
exception of bread, are cheap; at Cardona, mutton and beef costs | real vell. per 12 oz.
Bread of the best quality costs 1 real vell. per 12 oz. Wine of the country (a very
good red sort) is retailed at 6 quartos per bottle, or about two pence sterling.

VOL.. Ili; 3 F

410 Dr. TRAIL on the Salt Mines of Cardona.

ration reduces it into an excellent culinary salt of a snowy white-
ness. In this state it is sold to the peasantry of the surrounding
districts, at the rate of thirty reals vellon, or seven sh. six d. sterl.
per fanega of five arrobas of Catalonia, which equal 116 pounds
avoirdupois.

As there are no roads practicable for wheel carriages in this part
of Catalonia, the salt is carried from Cardona on mules or asses ;
the only beasts of burden that could travel in safety the rugged
defiles in which this district abounds. It seems a part of the perverse
policy of the Spanish government to discourage the formation of
proper roads, lest it should facilitate the operations of the smuggler.

It would not be difficult to connect Cardona, by means of a
canal, with the ocean; and thus the valuable produce of its salt
mines might increase the revenues of the crown, and the trade of
Barcelona. The channels of the Cardonero and Lobregat always
contain a large body of water, and might easily be rendered sub
servient to the purposes of inland navigation. Besides augmenting
the value of the mines of Cardona, such a plan, by facilitating the
intercourse with the interior of this fine province, would stimulate
the exertions of a people who only require an equitable govern-
ment to become highly industrious.

It yet remains that I offer a few remarks on the nature of the
country around Cardona, as materials for its geology.

Its general appearance is mountainous. The mountains are
abrupt, but generally wooded. The vallies are narrow, and,
where the declivities will permit cultivation, they produce abundance
of good grapes and some corn. In coming from Barcelona, the
traveller leaves, at a small distance on the left, the majestic Mont-
serrat ; and gradually approaches a mountain chain proceding from

Dr. TRAILL on the Salt Mines of Cardona. 411

its northern extremity, which declines as it stretches towards
Manresa. This chain consists of similar materials to Montserrat ‘5
viz. of vast beds of farcilite, composed of rounded masses of quartz,
with angular pieces of siliceous slate, and fragments of clayslate
united by a basis containing calcareous earth. The fragments of
this farcilite become smaller as we go northward, and at last bear
a striking resemblance to coarse greywacke; to which formation
I am inclined to assign the puddingstone of Montserrat, and the
chain of which it forms a part.”

On descending the rugged mountains of puddingstone into the
valley of the Lobregat, before coming to Manresa, we observe
strata of a bluish grey rock with interposed layers of a softer material
of the same colour, which crumbles into sandy clay by exposure to
the weather. These strata have some resemblance to sandstone-flag ;
but an attentive consideration convinced me that they ought to be
considered as stratified greywacké approaching to greywacké slate.
Above these we again find the farcilite, which is the prevailing rock
about Manresa, All the rocks hitherto mentioned effervesce slightly
with acids; a circumstance which connects them in some measure
with the extensive limestone country to the south-west of Mont-
serrat ; and they all shew a tendency to split vertically into columnar
masses. Beyond Manresa the farcilite occurs till the traveller crosses
the ford of the Cardonero, when it is succeeded by a limestone of a
dirty iron brown colour, and dull, almost earthy, fracture. Beyond

* It may not be improper here to remark, that the common descriptions of Montserrat,
are in several respects erroneous. It is not an insulated mountain, as generally repre-
sented ; but is the highest point of a considerable chain, Its insular appearance, as seen
from the high road between Igualada and Martorel, has deceived those who have never
examined its north-eastern side, The ¢ouchstone, mentioned by Bowles and others, as
entering into the composition of its puddingstone, appears by its fracture to be only a
dark coloured common siliceous slate.

Br?

412 Dr. TRAILL on the Salt Mines of Cardona.

the village of Suria, a sandstone, which slightly effervesces with acids,
makes its appearance. ‘This rock constitutes the sides of the valley
which contain the fossil salt.

The immediate vicinity of the salt mines shews no other rock than
a yellowish grey sandstone much charged with scales of mica.

We find thus that the salt rock of Cardona is accompanied by
clay and sandstone, like our Cheshire salt formation. Limestone
also is found near it; but the usual concomitant gypsum appears to
be wanting, as well as foetid limestone. The great compactness and
purity of this salt merits examination.

Though the country around Cardona is mountainous and rugged,
it is inferior in elevation to the districts between it and the Mediter-
ranean; as well as to those which bound it on the north. Imme-
diately behind Cardona the mountains begin to ascend with increas-
ing boldness until they unite with the grand chain of the Pyrenees.

I relinquish to others the difficult task of giving a probable
explanation of the formation of rock salt; contented if my obser-
vations on the mine of Cardona can add any thing to the mass of
facts which should guide us in the obscure but captivating specu-
lations of geology.

XIV, Description of a New Ore of Tellurium,

: By PROFESSOR ESMARK,
OF CHRISTIANIA,

FOREIGN MEMBER OF THE GEOLOGICAL SOCIETY.

[Read June 16, 1815.]

Lt occurs coarsely disseminated, and crystallized in perfect hex-
agonal plates striped on the edges.

It has the whitish hue of tin.

Its fracture displays a perfect foliation, but only in one direction.

It has a strong metallic lustre; a moderate flexibility ; consider-
able softness, and feels heavy.

Before the blowpipe it burns with the colour and smell of tel-
lurium, and has the same action with acids. The precipitate by
water burns upon charcoal like tellurium; but after its sublimation
a small metallic button remained of the colour of silver, malleable,
but too minute for further examination; for on account of the
rarity of the substance, I could only devote a single grain to this
examination.

It is found in the Orndal copper mine, accompanied by copper
pyrites, and a small intermixture of sulphuret of molybdenum.
The mine is called Mosnap, and has been full of water for several

414 Proressor EsMARK’s Description of a new Ore of Tellurium.

years. The vein lies in mica slate. I met with the same ore in
Hungary, in the collection of my friend M. Gerhard, who gave
me a specimen of it; but as he did not know from what part of
Hungary it came, he did not value it. For this reason I omitted
taking notice of it in the journal of my travels through Hungary
and the Bannat of Temeswar.

It is easily distinguished from molybdena, by its colour and its
habitude before the blowpipe.

XV. An Account of the Swedish Corundum from Gellivara, in
Lapland.

‘By C. T. SWEDENSTIERNA, or Srockuoum,

FOREIGN MEMBER OF THE GEOLOGICAL SOCIETY.

[Read January, 21st, 1814. ]

In the spring of 1803, when examining a series of iron ores from
Lapland which I had brought with me to Paris, I was greatly sur-
prized to find that the porphyry mortar employed in reducing one
of them to fine powder was scratched and lost its polish, Mr.
‘Tennant having nearly at the same time published his discovery on
the identity of emery with the sapphire, I was at first induced to be-
lieve that the said ore was merely a kind of emery. Upon a fur-
ther examination however, I found that this ore was as soft as any
other from the same place, and was chiefly composed of black and
red oxide of iron. These could be separated by the magnet without
leaving any earthy residue, which would not have been the case with
emery, in which the cutting substance is finely divided and inti-
mately connected with the oxide. I afterwards broke several spe-
cimens of the ore, and perceived in some of them very hard crystals
the largest of which were of the size of small peas, and exhibited
regular faces of an oblique octohedron. I at last succeeded in ex-
tracting about half a dozen of them of a perfectly determined form,
I then no longer doubted of these crystals being a variety of corun-
dum, which also was ascertained by my teacher in mineralogy, M.
Haiiy, to whom I presented the purest and most perfect specimens

416 M.SwrEpENsTIERNA on the Corundum of Gellivara.

I had got, and some of which have since obtained a place in the
museum at Paris, and have been mentioned in the catalogue of Mr.
Lucas, p. 132, under the name of Corindon Harmophane base. The
few remaining specimens, being all of an inferior quality, I gave to
my mineralogical friends, keeping but a single crystal for my own
collection, in the hope that on my return to Sweden I should easily
procure a fresh supply from a large stock of Gellivara iron ore in
my possession. In this expectation however I have been for the »
last ten years disappointed, and it is only within a few days that my
search has been successful enough to furnish me with sufficient ma-
terials for a satisfactory déscription of this substance. The few but
very excellent specimens now in my possession, and which will per-
fectly serve this purpose, I have been so fortunate as to pick out of
several hundred pounds of Gellivara iron ores, for which I am in-
debted to Bar. Hermelin, the proprietor of the mines. It is rather
singular that with the exception of the specimens I have mentioned,
I did not discover a trace of corundum in the large quantity which
was examined. I am led to believe therefore that it is by no means
common, or at all events that the mines which are now worked do
not furnish it in abundance. The specimen which accompanies this
short memoir, and which I have the honour to present to the
Geological Society, is the best and most complete among them all.

Oryctognostic description of the Gellivara Corundum.

When perfectly cleared of the grayish dust of the iron ore in
which the crystals are imbedded, their colour is exactly that of
common French flint.

The only form in which it has hitherto been found is that of an

M. SWEDENSTIERNA on the Corundum of Gellivara. 417

oblique octohedron, more or less complete, from the size of a pin’s
head to that of about three lines across. Very often the crystals.
are so much compressed that they exhibit to the naked eye only
two large faces, the lateral ones being then almost imperceptible.
Sometimes the crystals are grouped two or three together, and
striped parallel to the great diagonal. -

, The external lustre is accidental, being mostly hid by the fine
powder of the matrix covering the surface, but in a fresh fracture
the internal lustre is very brilliant.

The cross fracture is uneven, though approaching to the laminar.
The longitudinal fracture is perfect laminar, in which direction it
_also can be easily divided.

The small fragments are in general undetermined, more or less
pointed, often taking the form of a rhomboidal prism, the four
faces of which exhibit a specular gloss.

It is semitransparent, though not so much as French flint.

Its hardness is the same as that of corundum from India.

It breaks easily in the direction of the lamina, but in other di-
rections not without some difficulty.

The specific gravity of two specimens was 4.20 and 4.02.*

At the blow-pipe it cannot be melted, neither. alone nor with
borax, &c.

Its most common and immediate matrix is a light grey coloured
laminar iron ore, consisting of an intimate mixture of red and black
oxide of iron, without any visible earth. This ore (a variety of
eisenglanz, Werner,) which has been mentioned by Count de

* The specimens were very small, the one weighing only 1.93 grains English, the other

0.63 of agrain. They were cut and polished in order to free the substance from the iron

ore with which the crystals are in general mixed.

=~

Won. Iii. 3G

418 M. SwEprensTIERNA on the Corundum of Gellivara.

Bournon in the Philos. Trans. 1803, is often accompanied by
another coarse grained, half crystallized, loose, and more magnetic
ore, by red felspar, red and white grayish phosphate of lime, and
silvery coloured mica. ‘The corundum may sometimes be found in
the last mentioned iron ore, but never in the other substances,
though they often make a great part of the mass. Nor has it been
observed in any other variety of the Gellivara iron ores, except in a
light grey coloured, fine grained, compact and very hard one, where
- I suspect it to be in the same close connection with the red oxide
of iron as in the common emery, to which it has a great resem-
blance.

Geographical and Geological Sonate

The mines of Gellivara are situated in Swedish Lapland, at
67° 10’ North latitude, about 160 English miles north-west of
Torneo. ‘The mountains in which they are wrought is almost in
the center of a large country comprized between the shore of the
Baltic and the Norwegian Alps, 240 miles in length, and between
the two rivers of Torneo and Luleo, from 35 to 100 miles broad.
The height above the Baltic is not exactly determined, but may be
supposed about 1200 feet at its highest point. It rises gently on
the south side, but is more abrupt on the north and east. The
surrounding country is but a few hundred feet lower, and a moun-
tain called the Dundary, at a distance of five or six miles to the
east, is much higher. The whole mountain, which is about 2600
fathoms in length and from 1000 to 1600 in breadth, may be con-
sidered as a large deposit of iron ore, separated in standing layers
(Stehende Lager, Werner) of different thicknesses, by a red and
almost compact feldspar mixed with several other minerals. This

M. SwEDENSTIERNA on the. Corundum of Gellivara. 419°

red felspar, in a fine grained combination with quartz and mica, is
the common rock of the country, which however is never here ~
found uncovered. It occurs only in detached blocks as well at the
foot as at the highest top of the mountain, which is besides par-
tially covered with a fine white sand to a considerable depth; with
siliceous gravel and small blocks of amorphous garnet with specks of
iron. Slaty quartz is also found in small fragments, but never
forming a solid rock.

The above mentioned layers of iron-ore have in all the mines and
all over the mountain a general direction from north-east to south-
west, dipping about 45° to north-west. They very often stretch
several hundred fathoms in length, and from two to three hundred
in breadth, merely covered by a slight vegetation of mosses, If we
except the red felspar, which at small distances runs parallel with
the ore and sometimes crosses its layers, the whole forms almost a
solid mass of iron, of a very considerable extent, and of an unknown
depth. In those places where the ore is of a loose texture and
either coarse or fine-grained, a large quantity can in an hours time
be dug up by a spade. The more hard and compact magnetic ores
break generally in rhombs, the angles of which are about 45°, or
equal to the dipping of the layers. i

The ores, of which I hope to give a more detailed account at
another time, form the most complete series of iron in different de-
erees of oxidation, from the almost black magnetic ore to the light
gray not the least magnetic, (eisenglanz, Werner,) -the true sub-
stance of which shews itself by its red colour when rubbed. The
greatest number of ores forming this series, may probably be con-
sidered as a more or less intimate though merely mechanical com-
bination, between the two varieties of iron in its minimum and
maximum of oxidation, The variety mentioned by Count de

8G2

420

M. SWEDENSTIERNA on the Corundum of Gellivara.

Bournon may be taken perhaps as an instance of the combination

in which the red oxide is found in the greatest quantity.

The minerals which occur at Gellivara, besides the corundum, in

the feldspar separating the layers or within them, are chiefly the

following.

1. White or grayish calcareous spar.

2. Small calcareous crystals.

3. Ditto siliceous ditto.

5, Green glassy actinolite, sometimes crystallized in four-sided
prisms.

5. White pretty hard asbestus.

6. White yellowish phosphate of lime, nearly of the same colour
as the corundum, commonly imbedded in a black blueish
magnetic ore, forming almost one half of it, and giving
to the whole mass a singular appearance.

7. Red phosphate of lime of a rosy tint and granular form. In
some of the specimens I brought with me to Paris, I
discovered some small but very regular hexahedral prisms
of this substance, which I never met with afterwards.

8, I might also add several varieties of quartz and mica, which

however mostly form with the felspar either gneiss or

granite.

P.S. Since writing the above memoir I have again examined the

Gellivara iron-ore, and have found amongst it some specimens of

true emery.

A LIST OF DONATIONS
TO THE
COLLECTION OF MAPS, PLANS, SECTIONS,
AND MODELS;

AND TO THE
CABINET OF MINERALS,

BELONGING TO THE

GEOLOGICAL SOCIETY,

From the Close of the Seventh Session in June, 1814,
to the Close of the Ninth Session in June, 1816.

TOGETHER WITH THE DATES AT WHICH THEY WERE RESPECTIVELY MADE,

AND THE

‘NAMES OF THE DONORS.

I. Donations to the Library.

1814. DONATIONS. DONORS.
July 8. Catalogus Bibliothece Historico-naturalis Josephi Sir Joseph Banks, Bart.
Banks, Regi a consiliis intimis, Baroneti, Balnei
Equitis, Regie Societatis Presidis, caet. Auctore
Iona Dryander, A.M. Regie societatis Bibliothe-
cario. Tomus IV. Mineralogi.
Londini, 1799. 8°
Aug. 16. Journal de Physique in continuation to June, 1814. Robert Ferguson, Esq.
Memb. G. Soc.
Sep. 2. Laws of the Cornwall Geological Society, instituted John Ayrton Paris, M.D.
at Penzance, Feb. 11th 1814.
Penzance, 1814. 12°
6. On the Geological system of Werner. G. B. Greenough, Esq.
London, 1813. 8° Memb. G. Soc.
A Catalogue of the Minerals in the Museum of Robert Hutton, Esq.
Trinity College, Dublin. Part I. containing the Memb. G. Soc.
Systematic Collection. Dublin, 1807. 8°
System of Mineralogy ; by Prof. Berzelius. Thomas Thomson, M.D.
Hon. Memb. G., Soc.

422 LIST OF DONATIONS.

1814. DONATIONS,

Oct. 116 Tableau Methodique des Espéces minerales; Pree
miere Paftie; par J. A. H. Lucas, Garde des Ga-
leries du Museum d’Histoire naturelle de Paris,
&e. Paris, 1806. 2 vols 8°

Journal des Mines, in continuation for January,
February, March, 1814.

Annals of Philosophy, No. 16, 17, 18, 19, 20,
21, 22, 23; by Thomas Thomson, M.D.

Dec. 2. Storia naturale della Sicilia dell’Ab. Francesco
Ferrara, primario professore di Fisica nella regia
universita di Catania dott. di Filosophia, e me-
dicina e socio di varie accademie.

Catania, 1813. 4°

Resultate der Untersuchungen uber die harte und
Specifische Schwere der Mineralien; von D. L.
Pansner. St. Petersburg, 1813. 8°

13. Memoire sur la determination directe d’une nou-
velle variété de forme cristalline de chaux car-
bonatée et sur les proprietés remarquables qu’elle
presente ; par M, Monteiro. 4°

Essai sur la valeur des caractéres physiques em-
ployés en mineralogie; par J. Pelletier, Phar-
macien, Docteur en sciences, Membre des So-
cietés de Medicine et de Pharmacie de Paris,
etc, etc, Paris, 1812. 4°

A manuscript memoir on the Antilles; by F. L.
Herminier, Chimiste Pharmacien a la Basse
Terre Guadaloupe.

16. Nouvelle description mineralogique du pyromeride
globaire, ou de Ja Roche connue sous le nom de
Porphyre globuleux de Corse; par M. Monteiro,

Uber die gewohrdichste Zwillingskrystallisation
des Feldspathes vom Professor Weiss in Berlin.

Notes sur des Empreintes de corps marins trouvéesa
Montmartre, dans plusieurs couches de la massé
inferiéure de la formation gypseuse ; par M. M,
Constant, Prevost et Anselme Desmarest.

1815. 1809. 8°

Jan. 6. Memoire sur la Gyrogonite; par M. A. G, Des.
marest fils, Membre de la Societe philomathique
de Paris. 1810. 8°

Extrait D’un Rapport, lu en adut 1812, a la
Societé philomatique de Paris; par A, G, Des-
marest, sur un Mémoire de M, Daudebard de
Ferrussac intitulé ; Considerations générales sur
Jes Fossiles des terrains d’eau douce. Paris. 8°

Memoires sur les couches naturelles de Passy ; par
M. A. ‘G. Desmarest, Paris, 1813, 8°

Memoires d’Agriculture ; d’Economie rurale et
Domestique, publiés par la Société @’ Agriculture
ou Department de la Seine, tome iv.

Paris, 1801. 8°

DONORS,
The Author.

Le Conseil des Mines.
The Editor,
The Author,

The Author

The Author

Henry Heuland, Esq,
Memb. G, Soc,

The Author.
For. Memb. G. Soe,

The Author,

M, Leopold Von Buch,
For. Memb. G. Soc,
The Authors,

The Author,

owe <@ = ©

“

LIST OF DONATIONS.

$815. DONATIONS.

Jan. 6. Systéme des Animaux sans vertébres ou Tableau
général des classes, des ordres et des genres de
ces animaux; par J. B. Lamarck de l'Institut
national de France, &c. Paris, 1801. 8°

20. Memoires pour servir a l’Histoire naturelle et
principalement a l’oryctographie de l’Italie, et
des pays adjacens ; par Albert Fortis, un des 40
-de la Societé Italienne, &c.

Paris, 1802. 2 vols. 8°
Storia e fenomeni del Vesuvio esposti Dal P. D.
Gio: Maria della Torre Chir. reg. somasco,
professore di Fisica dell’ Accademia, Arcives-
covale di Napoli, &c. Napoli, 1755. 4°
Mineralogical Nomenclature, alphabetically ar-
ranged, with Synoptic tables of the Chemieal
analyses of Minerals; by Thomas Allan.
Edinburg, 1814. 8°
A Manuel of Mineralogy; by Arthur Aikin, Secre~
tary to the Geological Society.
London, 1815. 2d edit, 8°
#2). 12. Description methodique d’une Ceilection de mine-
raux du Cabinet de M. de Romé De Lisle.
Paris, 1773. 8°
Memoire sur les Ossemens et coquilles Fossiles
des environs de Plaisance; par M. Bruun-

Neergaard. 8°
Theorie: de la Terre, par Jean-Claude Delame-
therie. Paris, 1797. 2d edit. 8°

22. Catalogue systematique de la Collection de Petri-
fications, formée par feu M. Jean Conrad Am-
mann, Docteur en medicine a Schaffouse.

Nuremberg. 8°

. Reise auf die Gisgebirge des Cantons Bern De

Mar. 3. Observations sur les pierres meteoriques ; par M.
Lamboten. Paris, 1814. 8°

Three Copies of a Memoir, explanatory of the
Chart and Survey of the County of Londonderry,
Ireland; by the Rev. George Vaughan Sampson.

London, 1814. 4°

Notice sur le Corindon rouge-jaunatre, de Traver-
selle, vallée de Brozzo; sur le Plasma de Loca-
cana, meme vallée: sur le Manganese couleur
de rose de Picar-pra, vallée de Soana: objets qui
n’avaient pas encore été découverts en Piemont;
par Antoine Vagnon.

A Geological Essay on the Imperfect Evidence in
support of a Theory of the Earth, deducible
either from its General Structure or from the
changes produced on its surface by the opera~
tions of Existing Causes; by J. Kidd.

A423

: DONORS,
The Hon. H. G. Bennet,
Vice Pres.G. Soc.

G. B. Greenough, Esq.
Memb. G, Soc.

oe, ae Te ee

The Author.

The Author

Henry Warburton, Esq.
Vice Pres. G. Soc.

The Hon. H. G. Bennet,
Vice Pres, G. Soc.

G. B. Greenough, Esq.
Memb. G. Soc.

J. F. Berger, M.D.
Memb. G. Soc.

Henry Heuland, Esq.
Memb. G. Soc.
The Author,

Augustus Bozzi Granville,
M.D.
For, Sec. G Soe,

The Author.

424A LIST OF DONATIONS.

1815. DONATIONS.

April10. Exposition des operations faites en Laponie pour
Ja determination d’un are du meridien en 1801,
1802 & 1803; par M. M. Ofverbom Suanberg,
Holmquist, & Palander, redigée par Jous Suan-
berg, et publié par Academie des Sciences.

Stockholm, 1805. 8°

May 1. Annals of Philosophy: No. 29.

Journal des Mines, from April to Dec. 1814.

A. Practical treatise on Gas light: exhibiting a
summary description of the apparatus and machi-
nery best calculated for illuminating streets,
houses and manufactories with carburetted Hy-
drogen, or Coal gas; with remarks on the utility,
safety, and general nature of this new branch of
civil economy; by Frederic Accum, Operative
Chemist, &c. London, 1815. 8°

Meteorological diagram and Table for 1814, kept
by Lord Gray at Kinfaun’s Castle, North Britain.

Prospectus of a Survey of Perthshire ; by Professor
Jameson.

19. Journal de Physique, in continuation, to March
1815.
July 1. Notes made during a Geological Tour through
France. Manuscript.
Aug. 9. Geologie of Verhandeling over de Vorming en
Vervonning der Aarde
Oct. 20. Memoirs of the American Academy, vol. 3, part 1
and 2.
Mineral System of Werner, in Manuscript.

Nov. 3. Journal de Physique, in continuation, from April
to August, 1815.

Annals of Philosophy; by Thomas Thompson,
M.D. &c., in continuation, from August to
November, 1815.

Journal des Mines, in continuation, for April and
May, 1815.

Handbuch der Mineralogie von Ifoffmann.

Freiberg, 1815. 2 vols. 8°

Voyage a V’isle d’Elbe, suivi d’une notice sur les

autres isles de la mer tyrrhénienne; par Arsenne

Thichaut de Berneaud, Secretaire émérite de _

la Classe de Literaturé, Histoire & Antiquités
de l’ Academie Italienne, &c. Paris, 1808. 8°

Sui Sistemi Geologici Riflesioni analiteche del Cav.
Ermesgildo Pini., Professore di Storia nat, &c.

Uber die Aechtheit der Kristalle von August.
Breithaupt.

An Account of the Trigonometrical Survey, carried
on in the years 1791, 1792, 1793, 1794; by
order of the Master General of the Ordnance.

London, 3 vols. 4°

Annals of Philosophy ; by Thomas Thomson, N°.36.

DONORS,
Captain Colby,
Memb. G., Soc.

The Editor,
Le Conseil des Mines
The Author.

John Mac Culloch, M.D.
Pres. G. Soc.

Robert Ferguson, Esq.
Memb. G. Soc.

The Ion. H. G. Bennet,
Vice Pres G. Soc.

Leonard Horner, Esq.
Memb. G. Soc.

The American Academy.

J. H. Vivian, Esq.
Memb. G. Soc.
Robert Ferguson, [sq.
Memb. G. Soc,
The Editor.

Le Conseil des Mines

Aug. Bozzi Granville, M.D.

For. Sec. G. Soc.

The Author.

Capt. Colby, Royal Engin.
Memb. G. Soc.

The Editor,

LIST OF DONATIONS.

1815.
Nov.

; DONATIONS.
3 Account of the Structure of the Table mountain,
and other parts of the Peninsula of the Cape ;
by Captain Basil Hall, r. N. F.R.S. Edin,
Edinburg. 4°
Chemical Essays, Sel relating to the Arts
and Manufactures of the British dominions; by
Samuel Parkes, r.t.s. Mem. G, Soc.

London, 1815. 5 vols. 12mo.
5. A Treatise on the External Characters of Fossils,
translated from the German of Abraham Gottlob
, Werner, Counsellor of Mines, Professor of Mi-
neralogy, Public teacher of the art of mining in
the Mine Academy of Freyberg, and member
of several learned societies ; by Thomas Weaver.
Dublin, 1805. 8°
Syllabus of a Mineral System for a Course of Lec-
tures; by Prof, Giesecke. Dublin, 1815. 8°
Annals of Philosophy; by Dr. Thomson, N°. 37.
Journal des Mines for January and February 1815.
Elements of Conchology according to the Linnwan
system, illustrated by 28 plates drawn from
nature ; by the Rev. E.T, Burrow, Mem. G. Soc.
London, 1815. 8°

8. Journal de Physique, for September, 1815.

1816.
Jan.

18, Journal de Physique, for October, 1815.
Journal des Mines, for May, June, July, 1815.
31. Annals of Philosophy; by Dr. Thomson, for
February, 1816.

“Feb. 2. A Treatise on the mineral waters of Gilsland ; by :

W. Reid Clanny, M.D, M.R.J.A. &c.
Sunderland, 1816. 8°
12. Meteorological Table, for 1815, from a register
kept by Lord Gray at Kinfauns Castle.
Journal des Mines, No. 224.
23. Journal de Physique, for Nov. and Dec. 1815,

March 1. The American Medical and Philosophical Register,
or, Annals of Medicine, Natural History, Agri-
culture, and the Arts; conducted by David
Hosack, M.D. F.L.S. Professor of the Theory
and Practice of Physic and Chemical Medicine
in the University of the State of New York, &c.
and John W. Francis, M.D. Professor of Mate-
ria Medica in the University of the State of
New York, &c. New York, 1814. 4 vols. 8°

Annals of Philosophy ; by Dr. oes for March,
1816.

13. Voyages Mineralogiques dans le Gouvernement

d’Aigle et une partie de Valais; par M. le

Comte de Razoumowsky. Lausanne, 1804. 8°

VOL. Ill. 3°

425

DONORS.
The Author.

The Author.

The Translator,.

Robert Hutton, Esq.
Memb. G. Soc.

The Editor.

Le Conseil des Mines

The Author.

Robert Ferguson, Esq.
Memb. G. Soc.

Le Caiiaett ie Mines

The Editor

The Author.
John Mac Culloch, M.D.

Pres. G. Soc.
Le Conseil des Mines.

. Robert Ferguson, Esq.

Memb. G. Soc.
J. W. Francis, M.D. &c.

The Editor.

G. B. Greenough, Esq.
Memb, G. Soc.

426 LIST OF DONATIONS.

1815. DONATIONS,
Mar.15. Geological and Mining Report on the Leinster
Coal District; by Richard Griffith, jun. Esq.
Inspector General of His Majesty’s Royal Mines
in Ireland, Mining Engineer to the Dublin So-
ciety, &c.
25. Journal-de Physique for January, 1816.

April 5. Introduzione alla Geologia; di Scipione Breislak,
Amministratore et Ispettore de’nitri e delle
polveri del regno d’Italia, socio di diverse Acca-
demie. Milano, 1791. 2 vols. 8°

Journal de Physique for February, 1816.

De Arragonite ejusque differentia a Spatho calcereo
rhomboidali, Chemica commentatio, recitata in
concessu societ. reg. scient. A Frid. Stromeyer.

4°
15. Thirteen Numbers of the Gottingen Magazine.

Descrizione dell’eruzione del Vesuvio avvenuto
ne’ giorni 25 e 26 Decembre dell’ anno 1813;
dal Theodoro Monticelli, Secretario perpetuo
della Real Academia delle Scienze.

Napoli, 1815. 4°

Practical hints on the application of wire gauze to
lamps, for preventing explosions in Coal mines ;
by Sir Humphry Davy, LL.D. F.R.S. &c.

London, 1816.: 8°

Kurze Beschreibung einer mineralogischen Reise

durch Ungarn, Siebenburgen und das Bannat ;

von Jens Esmart. Freyberg, 1798. 8°
Annals of Philosophy for May, 1816; by Dr.
Thomson.

Catalogue raisonnée des diamants dans le Cabinet
de Sir Abraham Hume, Bart.; par M. le Comte
de Bournon, Memb. G. Soc.

Journal des Mines, No’s. 225, 226, 227, 228.

DONORS.
The Author.

Robert Ferguson, Esq.
Memb. G. Soc.
The Author.

Robert Ferguson, Esq.
Memb. G. Soc.
The Author.

eve

The Author.

The Author.

S. Solly, Esq.
Memb. G. Soci

The Editor.
The Author.

Le Conseil des Mines.

II]. Donations to the Collection of Maps, Sections, &c.

1814.
Oct. 10. Map of Londonderry.

Dec. 16. Carte Géologique du department de l’Ourte.
23. Map of the World on Mercator’s projection.
1815.

Jan. 6. Thirty-two Maps of the different departments of
France.

The Rev. G. V. Sampson,
Hon. Memb. G Soc.
Alex. Henderson, M. D.

Memb. G. Soc,

‘Leonard Horner, Esq.

Memb. G. Soc.

Hon. Henry Grey Bennet
V.P. G.Scc.. ;

Right Hon. Earl Compton,
V.P.G. Soc. &

G. B. Greenough, Esq.
Memb. G. Soc

1815.
Jan, 20.

>

Feb. 22.

M arch 3.

21.

April 7.

10.
12.

May 19.

Aug. 9.
Oct. 30.

Nov. 3.

22.

March1.

15.

LIST OF DONATIONS.

DONATIONS.
Map of Normandy in 4 sheets.

Engraved Portrait of Deodat de Dolomieu.

Model of the Pedestal of the Statue of Czar Peter
the Great in Petersburgh, of the same granite as
the statue. ©

Section of Cyfartha coal mine.

Section of Chicksgrove quarry, Tisbury, Wiltshire.

Horizontal Section of the coal and part of the
limestone measures on the South-east side of the
Basin in Dean Forest.

Engraving of a Fossil found in the cool strata near
Bristol.

Bas relief formed by a tufaceous Deposition in a
mould from Italy.

A Drawing of Vegetable remains preserved in cal-
cedony.

Pattern of a Mineralogical hammer.

Sketch of a Portrait of Professor Werner.

Engraved Portrait of Professor Werner.

Werner’s table of Colours for Geological Maps.

Plan of the Ashton under Lyne, Peak Forest,
Huddessfield, and Rochdale Canals.

Plan of the Gloucester and Berkeley Navigable
Canal.

Section of the Strata at Wyken Colliery near
Coventry.

Coloured Print of the Chara Vulgaris.

. Panoramic View from the summit of Snowdon.

Plan of the Mountain of Snowdon.
Section on the East side of Loam pit hill, near
‘Lewisham, Kent.

Drawing of Pitcairn’s island, copied from an ori-
ginal drawing in the possession of A. B. Lambert,

- Ksgq.

Carte de la Principauté de Neuchatel; par J. F.
Ostervald.

Corrected Section of Chicksgrove quarry, with
Specimens.

A volume of Drawings of Fossil Alcyonia, with a
description in manuscript.

3H 2

4237

DONORS.

Hon Henry Grey Bennet,
V.P. G. Soc.

Right Hon, Earl Comptdn,
V.P. G. Soc. &

G. B. Greenough, Esq.
Memb. G. Soc.

Hon. Henry Grey Bennet,
V.P. G. Soc.

Henry Heuland, Esq.
Memb. G. Soc.

William Dubois, Esq.
Memb. G. Soc.

Miss Benett.

David Mushet, Esq.
Hon. Memb. G. Soc.

Rey. James Townsend,
Hon. Memb. G. Sar.

Sir Henry Englefield, Bart.
Memb. G. ap. g

J. Mac Culloch, M.D.
Pres. G. Soc.

weer eere

J. H. Vivian, Esq.
Memb. G. Soc.

Henry Warburton, Esq.
V.P. .G. Soc.

William James, Esq.
Memb. G. Soc.
James Sowerby, Esq.
Memb. G, Soc.

Col. Mudge, R. Artillery,
Hon. Memb. G. Soc.

Rev. W. ‘Buckland,
Memb. G. Soc. &

Rev. W. Conybeare,
Memb. G. Soc.

G. B. Greenough, Esq.
Memb. G. Soc.

J. F. Berger, M.D.
Memb. G. Soc.
Miss Benett.

428

1816. DONATIONS.
April15. Ground plan, two Sections, and two perspective
Views of Cader Idris in North Wales.

May 17. Two copies of the Ordnance Map of the Isle of

Wight.
23. Two copies of the Ordnance Map of Cornwall.

LIST OF DONATIONS.

DONORS. €
Col. Mudge, R. Artillery,
Hon. Memb. G. Soc.

Ill. Donations to the Cabinet of Minerals.

1814.

July 8. Specimens from Cornwall, and the Vertebra of a
Whale found in the stream work of Pentowan,

Oct. 10. Specimens from Battle, in Sussex.

25. Specimens of Limestone with Fossil shells from
Plymouth.
Nov. 4. Native Iron from the Brazils, two specimens.

Two Septaria from Whitby.
Two Specimens of Calcareous incrustation.

Dec. 2. Specimens from Dudley, from Kinnoul, from the
Pentland hills, and from Salisbury craigs; and
recent Shells.

3. Fossil Organic remains from Maestricht.

16. Native Carbonate of Copper from Chessy.

23. Specimens of Zeolite from Ferroe, of Derbyshire
spar, and of Slate from Ingleton, Yorkshire.
28. Miscellaneous specimens from the Giant’s Cause-
way, Carlisle, &c.
30. Fossils from the Green sand near Warminster, and
other Fossil Organic remains.
1815.
Jan. 3. Fossil Organic remains from Clungunford, Shrop-
shire.
6. Fossil shells from France and Italy.

Cast from a Crystal of Blue Topaz, weighing 15 oz.
found in the mountains of Mar, Aberdeenshire.
_ Specimens of Tremolite and Sahtite from Glen Tilt,
23. Fossil Fistulana from the Coral rag, Calne.
Slag from a furnace.
Specimens from St. Helena.
Feb. 2. Fossil teeth and part of a Crocodile’s jaw, from
Stonesfield.
Fossil madrepore.

Pebble from Antigua.

Rev. John Rogers.

Hon. Henry Grey Bennet,
Pres. G. Soc.
Rev. Mr. Hannah, junr. .

Right Hon. Lord Dundas,
Memb. G. Soc,

Leonard Horner, Esq.
Memb. G, Sac.

Rey. E. Hony,
Memb. G., Soc.

Henry Heuland, Esq.
Memb. G. Soc.

Leonard Horner, Esq.
Memb. G. Soc.

Thomas Mead, Esq.
Memb. G. Soc.

Thomas Dugard, M.D.
Hon. Memb. G. Soc.
Hon. Henry Grey Bennet,

Pres. G. Soe.
J. Mac Culloch, M.D.
Memb. G. Soc.

Memb. G. Soc.
Thomas Botfield, Esq.
Memb. G. Soc.

S. Davis, Esq.
Memb. G. Soc,
Samuel Turner, Esq.
Memb. G. Soc.
Charles Stokes, Esq.
Memb. G. Soc.
Samuel Turner, Esq.
Memb, G. Soc.

1815.
Feb, 12.

aee

March 8.

17.

21

April 7.

LIST OF DONATIONS.

DONATIONS.
Fossil Organic remains and Specimens of strata
from the commune de Haut Goulain, France,
Specimens from Tino in.the Archipelago.

Twenty-one Specimens of simple minerals.

Specimens from a chalk-pit at Reach, near Cam-
bridge.

Specimens from France.

Specimens from Somersetshire.

Folsil tooth of a Crocodile from Stonesfield.

Geode from Oakhampton.

Subcarburet of iron, Mawnan glebe.
Fossil shell from Maestricht.

Crystallized slags from a furnace.
Specimens from Reading.

Specimen of the Elephant bed, Brentford.
Specimens of English strata.

Fossil Organic remains from Weymouth.
Fossil shells from Stifford in Essex.
Specimens from the neighbourhood of Dufton.

Recent shells.
Organic remains from Reach, the Isle of Ely, and

Wilham.

. Specimen of coal from Jamappe, of chalk from the

canal of St. Quentin.

. Fossil patella from Minchin Hampton.

. Specimen of Mountain limestone, three miles from

Newport, Gloucestershire.
Specimens of strata and Organic remains from
France.

. Specimens of English and Scottish strata.

Specimens of English strata,

Alcyonite in Calcedony.

. Freshwater shells from a gravel-pit in Moorfields.

Specimens of Calcedony from

Organic remains and Sulphat of Strontian,

429

DONORS.

Hon. Henry Grey Bennet,
Memb. G. Soc.

Leonard Horner, Esq.
Memb. G, Soc.

Henry Heuland, Esq.
Memb, G. Soc.

Rev. ft’. Holme,
Memb. G. Soc.

Hon. Henry Grey Bennet,
Memb. G. Soc,

Leonard Horner, Esq |

Memb. G, Soc.

Rey. William Buckland,
Memb. G. Soc.

Professor Hailstone,
Memb. G. Soc.

Rey. J. Rogers.

Rev. E. Hony,
Memb. G. Soc.

Samuel Turner, Esq.
Memb. G. Soc.

Rey. William Buckland,
Memb. G. Soc.

Miss Benett.

Rev. William Buckland,
Memb. G,. Soc.

Miss Benett.

Rev. William Buckland,
Memb. G. Soe.

Miss Benett.

Professor Hailstone,
Memb. G. Soc.

Knight Spencer, Esq.

Henry Warburton, Esq.
Sec. G. Soc.

J.E. Tyler, Esq.
Memb. G. Soc.

E. W. Rundel’, Esq.
Memb. G. Soc.

G. B. Greenough, Esq.
Memb. G. Soc.

G. B. Greenough, Esq.
Memb, G. Soc.

Right Hon. Earl Compton,
Memb. G. Soc.

A. Aikin, Esq.
Sec. G. Soc.

James Laird, M.D.
Memb. G. Soc,

Miss Benett,

June 2.

Oct. 30.
Nov. 3.

12.
16.

Dec. 1.

15.

1816.
Jan. 5.

LIST OF DONATIONS.

DONATIONS.

. Specimens of contorted Limestone from Glen Tilt.

Specimens from Essex of Fossil bones of the Ele-
phant, Hippopotamus, Elk, Stag, and Buffalo,
and of Shells from the Crag pits.

Coneretions found in a clay pit at Erith, Kent.

Fossil teeth of the Elephant, Hippotamus, and Ox,
from Essex and Suffolk.

Specimen of Chromate of Iron from Norway.

Specimen of Native Tellurium from Norway.

. Fossil Fish from Pappenheim.

. Recent Sandstone ; New quay, Lower St. Columb,

North Coast of Cornwall.

. Fossil Trochus from Highgate.
. Specimen of Iserine from the Cheshire shore oppo-

site Liverpool.

. Specimens from Chicksgrove quarry and Warminster

common.
Specimens of English strata.

Fossil-Organic remains from Weston Super Mare.
Spéckmets of Rock Salt from Cardona in Spain.
Specimens of simple minerals.

speutnnen from South Wales.

Slab of Marble from Chudleigh, Devonshire.

Calcareous incrustation from Cotton, near Cam-
bridge.

Specimens of Tufa, enclosing land shells, from
Stroud in Gloucestershire.

Specimens of Plymouth Limestone, with Organic
remains.

Specimens from the Western Islands of Scotland.

Specimen of Oxide of Uranium on Pech Blende.

Specimens of Curl-stone from Machynlleth.

Specimens collected in the East Indies by Capt.
Basil Hall.

Specimens of Calcaire grossiére from the Basin of
Paris. :

Specimens of the Plastic Clay formation, Silex
fe oe and Quartz nectique, from the Basin of

aris.

Fossil teeth of the Hippotamus.

DONORS.

J. Mac Culloch, M.D.
Memb. G. Soc.

Henry Warburton, Esq.
Sec. G. Soc.

T. Atlan, Esq.
Henry Warburton, Esq.
Sec. G. Soc.
Professor Esmark,
For. Memb. G. Soc.
A, Aikin, Esq.
Sec, G. Soc.
Ashhurst Majendie, Esq.
Memb. G. Soc.
Mr. Robert Pocock.
T. S. Traill; M.D.
Memb. G. Soc.
Miss Benett.

G. B. Greenough, Esy.
Memb. G. Soc.

G. Cumberland, Esq.
Hon. Memb. G. Soc.

T.S. Traill, Esq.
Memb. G. Soc.

J. H. Vivian, Esq.
Memb. G, Soc.

G. B. Greenough, Esq.
Memb. G. Soc.

Rev. William Buckland,
Memb. G. Soc.

S. L. Kent, Esq.
Memb. G, Soc.

Henry Warburton, Esq.
Sec. G. Soc.

Rev. R. Hannah, junr,

J. Mac Culloch, M.D.
Memb. G. Soc.

A. Champernown, Esq.
Memb. G. Soc.

Mr. Dawson.

Alexander Martet, M.D.
- Memb. G. Soc.
T. Webster, Esq.

Keep. Mus, G. Soc.

ee eeee

Henry Warburton, Esq.
Sec. G. Soc.

1816.
Jan. 5.

12,

26.
March 1.

15.

April 2,

15.

May 1.

A.

LIST OF DONATIONS.

DONATIONS.
Specimens of Coke.

Specimens of Plastic Clay from Reading.

Specimens of Plastic Clay from the Weald of Sussex.

Specimens in illustration of Mr. Bogg’s paper on
the Strata of Lincolnshire.

Specimens of Clay from Walton, cracking into
prisms.

. Specimens of Native arsenical Antimony.

Clay from Reading.

. Two Specimens of Prehnite Koupholite, from the

Aiguille du gouteé.
Specimens of Selenite from the Glaise at Ponton,

near Paris. "

Specimen of Granite and Mica-slate from Glen
Tilt.

Specimen of Stone found in the neighbourhood of
Paris, and uséd in that city for filtrating water.

Fossil Shells from Grignion,

Specimens from Litchfield.

Fossil Alcyonia from Warminster.
Crystallized Phosphate of Iron from Cornwall.

Fossil Shells from Blackdown.

. Recent Shells.

Specimen of Pechblende.

Fragments of Belemnites from the Chalk-pits at
Norwich, and pieces of Gravel from Hertford.
Specimen of a vein of Blende in the slate near
North Shields, and Specimens of burnt Shale.
Two Specimens of Entomolites, Specimen of the
Porodragus of Montfort, three univalve Fossil
Shells from Highgate, and Specimens of Septaria

from ditto.

Specimens of compact Carbonate of Lime and Mag-
nesia from the Meissner in Hessia, and of Sul-
phate of Strontian from Minden, Hanover.

Specimen of Fossil wood in Calcareous rock, from
Stretton on Dunsmore, Warwick.

A scarce variety of the Lyas near Lyme.

Wood tin in the matrix, from Trethurgy moor,
near St, Austle, Cornwall,

43]

DONORS.
J. Taylor, Esq.
Memb. G, Soc,
Rey. William Buckland,
Memb. G. Soc.
G. B. Greenough, Esq.
Memb. G. Soc,
Mr. Bogs.

Henry Warburton, Esq.
Sec. G. Soc.

Hon. Henry Grey Bennet,
Memb. G. Soc.

Henry Warburton, Esq.
V.P. G. Soc.

J. F. Berger, M.D.
Memb. G. Soc.

Hon. Henry Grey Bennet,
V.P.-G. Soe.

J. Mac Culloch, M.D.
Pres. G. Soc.

Right Hon, Sir J. Sinclair,
Bart,

Hon. Henry Grey Bennet,
V.P. G. Soc.

A, Aikin, Esq.
Sec. G. Soc,

Miss Benett,

J. H. Vivian, Esq.
Memb. G. Soc.

A, Aikin, Esq.
Sec. G. Soc.

Hon. Henry Grey Bennet,
V.P. G. Soc,

A. Champernown, Esq.
Memb. G, Soc.

Joseph Woods, Esq.
Memb. G. Soc.

S. Solly, Esq.
Memb. G. Soc.

C. Stokes, Esq.
Sec. G. Soc.

Professor Stromeyer.

Baden Powell, Esq.
Memb. G. Soc.

Rey. William Buckland,
Memb. G. Soc.

Ashhurst Majendie, Esq.
Memb. G. Soc.

432 LIST OF DONATIONS.

1816. DONATIONS.
May 17. Specimens from Hungary. :

Specimens of the Strata of the Table mountain at
the Cape of Good Hope, selected in situ by Mr.
Pohlman, Chemist, residing at Cape Town.

Specimens from the neighbourhood of Cambridge.

June 7. Harmotome from Strontian, Argyleshire, and of
Lepidolite in Primitive limestone from Scotland.

Fossil Organic remains from the Hotwells, Bristol.
Fossil bones from Bath.
Recent Shells.
Fossil Madrepore from Antigua.
Plymouth Limestone with Organic remains.
Specimens from the Greek Islands.

A series of Specimens from the neighbourhood of
Oxford.

Specimens from Cornwall.

‘Dr. Darwin.

DONORS.
Richard Bright, M.D.

Memb. G. Soc.
Hi. T. Colebrook, Esq.

Memb. G. Soc.

Rev. T. Holme,
Memb. G. Soc.

Rev. T. Holme,
Mewmb. G, Soc.

G. Cumberland, Esq.
Memb. G. Soc. |
C. H. Wilkinson, M.D.

Memb.G. Soc.
Charles Stokes, Esq.

Sec. G..Soc, ‘
Samuel Turner, Esq.

Memb. G. Soc.
Rev. W. Hannah,

Rey. William Buckland,
Memb: G, Soc. &

Rey. William Conybeare,
Memb. G. Soc.

Ashhurst Majendie, Esq.
Memb, G. Soc.

INDEX.

Arkin Arrnur, Esq. Observations on a‘bed of Trap occurring
in the colliery of Birch hill in Staffordshire : E

Alluvial Formations of the North of Ireland : : :

Alluvial land, small quantity in Sky

Analcime, found abundantly at Talisker in Sky :

Antrim, Description of the Sections presented by the Coast ae

Asbestus, its soft state while in the bed : rae.

Barbadoes, Dr. Sxey’s remarks on the structure of t °
Successive terraces of different elevations in
Barytes, Sulphate of, Vein of; in the limestone of Cannington

Park ‘ ¢ . ’
Basalt, stratified, enormous mass covering secondary striata in
the North of Ireland gil eu - 3
Extent of the area of, in tbe North of ceenn 1.88
Tabular, in the North of Treland : . 7.5

Columnar, in the North of Ireland, described

TUT

Large spherical mass of, enveloped in the chalk on the
coast of Antrim : :
overlying the chalk in Apttint and Dereg, described °
Basaltic Dykes, effect produced by their traversing chalk in
the North of Ireland. : :
remarkable one traversing the red eaindsione of
the. Coast of Antrim ,
Basaltic group of Mountains in the North- Rast of lelana de-
scribed 40 i
Bercrr, J. F. M.D. .On the Gealosieal Fealuiés of the North-
Eastern Counties of Ireland
On the Dykes of the North of reid
Bitumen, found in Barbadoes 5 : . ;
Blaven, in Sky; situation of the mountain so called haga:
VoL, ul. 31

Mr. Conysearr’s arguments in favor of its igneous origin

asi INDEX.

* Bocc, Mr. Epwarp. A Sketch af the Geology of the Lincoln-
shire Wolds. i
Bole or Ochre, occurs in beds in ik North of Ireland : ‘

Calcareous stalactites in caves in the trap in. the Isle of Rathlin
Cambridgeshire, The Rev. J. Hairston, on the Geology of
Carbon, an ingredient in some traps_, . . ‘
Carbonate of Lime, found in the trap,in Sky “ffsine ‘
Cardona, in Spain. | Dr. Trai on the Salt Mines of

Caves, numerous in the cliffs of see Senage strata at Loch Slapin,
in Sky. : . .

— abounding in stillet concretions, in Gly . °

Chabasite, found at Talisker in Sky . : . eff pac!

abundant at Storr in Sky . . Seesd-4 ‘
Chalk, ‘In the North of Ireland, described . . es
formation of the North of Ireland, described
extent of the formation of, in the North of Ireland
in the Lincolnshire Wolds, peculiar circumstance in the

_ springs of : . ‘ . . :
Chlorite slate, Mica slate path into, in “Sky ‘ . ;
Clay, beds of, in connection with the Salt of Cardona ;

Clay slate, Mica slate passing into, in Sky. : .
stratified with dark blue quartz rock, in Sky
interstratified with the beds of red sandstone; and

sometimes passing into graywacke slate, in ony ‘.

among the fleetz rocks of Werner >
effect produced by a — whin dyke hpi ot it,

in Antrim > , ‘ ‘ 7
Clinkstone, in Sky . °. :
-—— porphyry, occurs in » the North of falas 4
Clinometer, Lord Wresg Szymour’s Description ofone §. A
may be applied in guaging ‘ : .
Coal, occurs in Sky : : . .
found at Tyrone in eames ; ‘ etal ;
— Ballycastle in Ireland ; ; P :

—— altered by contact with greenstone in Staffordshire ‘

INDEX. 455

PAGE
Coal, pieces of, found in the alluvium of the Lincolnshire Wolds 398
—— formations of the North of Ireland, described ; : 154 -

—— measures, strata similar to those covering the, in England
found beneath the basalt in the North of Ireland. ; 129

Conformit Yy of primary and secondary strata in Sky : 50

Conglomerate, of the South Western, part, ef Sager a
described : wt : 356—358 —

Contortions, of the slaty strata a Ry ital och : ‘ / SAG

Conyzeart, Rev. W. Introduction to, Dr. Beregr’s account of
the Geological Features of the North
Eastern Counties of Ireland , : 121
Descriptive notes referring to the Outline
of Sections presented by a part of the

Coasts of Antrim and Derry. ‘ ; 196

Copper ore, found in the limestone of Somersetshire . 344—3523

Coruisk, Lake, in Sky , * 24
Corundum, C. T. SwepenstuirRna’s account of. shes ona Gelli

vara in. Lapland A d ‘) A c - __4Al5

Cuchullin hills, in Sky, deeeined . i t . oF eae 12

Geology of the . oe Tivere ey

Decomposition, of Trap assisted by tillage of the soil covering it 11

of the Red hills,in Sky more. rapid than the j

Cuchullin ’ . 2 ‘ A 14

Denudation, of Strata in athe Nout of Tiakand ’ ; 129—132

Derry, Description of the Sections presented by the Coast of 196
Dykes, in the North of Ireland, Dr. Berceron . . : : 223
‘their direction generally parallel . : ° . 224
cut through metallic veins 4 . : ; . 231
Rocks of which they are composed * : ° ° 228
Minerals found imbedded in. ’ er ie . 229

of Monte Somma i in Italy, described : 4 : 233
Elevations, of places in the North of Ireland, by Dr. Brncer 217
Epidote, found in Sky ; : ‘ . : 91
EsmArK Proressor, Description of a new. Ore Woh Tellurium. 413

31 2”

436 INDEX.

Fleetz rocks, in the North of Ireland, described A

Flinty slate, containing Ammonites at Portrush . : .

— covered by Trap in Sky F : . :

Fossil remains, of the Green sandstone of Ireland : -

- of the Chalk of Ireland : : -

Foy, mountain, near Carlingford, ns oe of Prin

tive hae 5 ; 4 a $ ‘ : “4
Garsven, mountain in Sky, durable nature of k :

— its base composed of Red sandstone ; :

‘ in Sky composed of large grained Greenstone :

Geology, may be of service to agriculture : s 4
Gillan, in Sky, order of the KES at ; : .

Glamich mountain, in Sky, consists of Syenitic Be and Clink.
stone ; :

‘affects the magnetic kiddie . ; 2

Glen Tilt. A Geological Description of, by Dr. Mac Cuttocu
——— connection of its granite with that of the Grampian
hills’ : -

General eplomnal Devseriptial df

PAGE

152
213

169
169

14
95
259

302
311

Granite, the prevailing constituent of the Mourne mountains 122—134

—— and Syenitic granite are geologically the same rock .
circumstances attending its contact with the stratified
rocks in Glen Tilt . . :
found:in the South Western part of Sbinteehire 4
veins, passing through Schist and Limestone in Glen Tilt
Graypon, The Rev. = on the Dykes of Monte Somma
in Italy :
Green sand, underlying the Chalk i in the North of reunid
reposes immediately on Lias in the North of Ireland

Greenstone, occurs in Sky. : Ses ot Bes : :
its characters there . . ‘
occurs in the North of fiend \ ‘ .

227

312
348
268

233
130
130

59

of the North of Ireland, described a te 184——204

Vein of in Glen Tilt — 3 : ; : ‘
porphyry, occurs in Sky : ; : : é

INDEX. ~. 437
PAGE
Greenstone slate, occurs in the Mourne mountains in the North
of Ireland g 3 d 142
Grecor, The Rev. W. On shea! Treinolite i Gurmabell 399
Greystone, occurs in the North of Ireland ; J 186
Greywacke, and Greywacke slate, in the North of alas haa
cribed 146
of Somersetshire, disoribed. mb Nan Horton 345
Gypsum, contained in large quantities in the red sandstone near
Watchet x “ “4 - " j F : - 375
I[artstone, Tur Rev. J. Woodwardian Professor, &c. on the
Geology of Cambridgeshire ‘ 243
Hornblende, crystallized in Sky j 59
——_—— -, found in the granite - of ae Mine
mountains : Fs 135
with Mica occurs in the North of eee 143
slaie, in the North of Ireland, described . 140
rock, in the North of Ireland, described 140
Horner, Leonarp, Esa. F.R.S. Sketch of the wpe isi of ie
South-Western part of Somersetshire . : i 88
Hypersthene, found in Sky ‘ . : . -66—92
in Aberdeenshire A ; z : 93
Ichthyophthalmite, found at Dunvegan in Sky . : ; 90
Induration, of Mineral substances after taking them from their
beds 5 : : ° 6 286
Treland, Geological porate of the Coasts of yes and Bee,
described - f A Z 196
Tue Rev. W. Conyseare on the Geclelsicl peaiuacs ac
the North Eastern Counties of 121
Dr. Bercer on the Geological Features of the North
Eastern Counties of e ; 121
and Scotland, similarity in the Sirutture of part ‘of 123—124
125—131
Function, remarkable one at Glen Tilt ; ¢ 274

438 —

INDEX.

Kenbaan cliffs, on.the Coast of Antrim, described @ *

Kyle ric’h,

District in Sky, consists of Quartz rock F
Mountain above, composed of dark blue Quartz rock

Laumonite, found in Sky : ; 4 . :
Lias. See Lyas.

Limestone,

\

bed of compact, containing shells, included between
beds of Quartz rock near Gatoast in Sky ; ;
and Sandstone alternating with Mica slate near

Bpaneres In skyy nich. ein yg) \s 24
its position and characters in Sky ‘
reposes on Syenite at Kilbride in Sky :

alternating with shell Limestone near Borrereg
its characters when.in contact with Syenite in Sky
its contact with Trap at Loch Eishort in Sky
primitive, in the North of Ireland, described
a subordinate member of the mica slate
formation in the North of Ireland : .
transition, in the North of Ireland, described
alternates with Transition. trap and Grey -
wacke slate, in the North of Ireland. ,

Fleetz, associated with the Coal formation, in the
North of Ireland, described ? . ;
abounding in veins of Granite, in Glen Tilt
fibrous, found in Glen Tilt . ; ‘ é

of Glen Tilt, described , , , :
containing Madrepores, interstratified with ates in in
Somersetshire 2 " 5 3

Beds of, enveloped i in slate, in patios res :
Quarries, in the South Western part of Somerset-
shire, described 5 4 ayaiag’ 3 4
near Halsey cross, described ‘ : P

large Vein of, in the conglomerate of Sasa traptshiel
of Cannington Park, described ves ; :
Columnar distinct concretions in, in Somersetshire
of Somersetshire, Organic remains in ‘

Lincolnshire Wolds, Mr. Boge’s Sketch of the Geology of

5 69 09
no =—

<a}

INDEX.

439
: ', PAGE
Londonderry, Primitive mountain chain of, described 125
Lyas limestone, in the North of Ireland, described 130
formation, in the North of Ireland, described : : 164
of the South-Western part of Somersetshire, described 367
its junction with the red sandstone in Somerseétshire 374
its most western point in England is East Lynch. 379
Lydian stone, found at Duntulm in Sky . : 98
Mac Cuttocs, Jonn, M.D. Sketch of the Mineralogy of Sky 1
———___—_—_—__———_ A Geological Description of Glen
Tilt . : : 5 : ‘ : : 259
Magnet, Various rocks in Glen Tilt attecting the : - 324
Marble, at Strath in Sky, described : : : d 101
Observations on various sorts of Statuary : . 104
—— of Sky varying in hardness from the Trap veins tra-
versing it . . : : . . ‘ 110
* - of Glen Tilt, ieamatea 282
Marle, Remarkable bed of, in the Green Saliitone ‘of penabd
derry ; . : - ‘ : 168
containing land shells j in Glen Tilt : é : 316
Mesotype, found in various states in Sky . . : 86
Mica slate, one of the oldest rocks in Sky 28
———— and Quartz rock generally alternating : : 28
its situation in Sky A . = 28
-—_—— found passing into Clay slate, Talc slate; ind Chlorite
slate, in Sky S . é . 29
-——— contact with other stratified och at Loch ihore~ 31
Numerous Trap veins in, in Sky SETA: 30
————_ very generally distributed over the North of fvcland 136
Mourne Mountains, in Ireland, described 122—134
Miulatioe, the name given in Ireland to the Green sand _ 130
Murloch Bay, on the Coast of Antrim, described 4 . 203
Nomenclature. Dr. Mac Cutzocn’s Observations on that of
certain rocks 7 : : : s : : : 335

440 INDEX,

PAGS
Organic remains, abundant in Barbadoes # Pringenint | 237
of the Chalk in Cambridgeshire ‘ : 250
of the Limestone of Somersetshire ° 5 369

- Pearlstone porphyry, occurs in the Basalt district of the North
of Ireland. ‘ : . - ° . ; ° 190

Pecherz, found in Cornwall f “ 113
Puiturs, Mr. W. On the 8 -: Uranium the promieran of
Cornwall é ‘ ¢ . : : 112
Pinite, found in porphyry near Glen Tilt ‘ : ‘ : 308
Pitchstone, of a singular character found in Sky : ; 94
soup: occurs in the basalt district of the North
of Ireland 5 : 22 9. 190
Porphyry, in the North of ideas deacealeatly , 52 143
occurs in the basaltic area of the North of oak 189
singular variety of, found in Glen Fernat : 310
Prehnite, occurs in trap veins in Sky : . : ° 80
Quantock hills, in Somersetshire, described 5 : : 339
Quartz rock, one of the oldest rocks in Sky f ; s 28
and Mica slate generally found alternating . 28
appears to have been stratified in Sky ‘ : 30
numerous Trap veins in, in Sky ; “as: = 30
in contact with and conformable to beds of red
sandstone, at Ord, in Sky , , 5 50
Limestone with shells between beds of ; : 31
Limestone and red sandstone alternating with . 31
contact of other stratified rocks with, at Loch
; Eishort, in Sky . 31
————— dark blue stratified wish beds of cleyslare ; $2
— superimposed on the granite in Glen Tilt - 303
—— passing into granite in Glen Tilt ¢ 7 : 293
Red hills, in Sky, described yy f ait i4—68
Red marle, in the North of Ireland, described : : ; 131

Red sandstone, its position, in Sky : : F , - 3

—_—-? 6] x

ee

INDEX.

Red sandstone, alternates with schist, at Loch Eishort in Sky
interstratified with beds of schist, in Sky
—— in Sky lie between limestone and quartz rock

—— its characters i . : :
———_-———— in the North of Ireland, deserted ,
——_———_ alternating with greywacke, at Scabro hill -

—— thickness of the formation of, at Strangford

3 Lough F ° : -

—— of Minehead, deecribaiie
—— marly, near Wotton Courtney, eeaiad

—— argillaceous, in Somersetshire, described ;
Sahlite, found in Glen Tilt "ONE
Salt mines, of Cardona in Spain, Dr. Premy’ S icon cian on the
Sandstone, upper bed of, in Sky 3 mt oe ; °
————— remarkable disposition of the strata of, in Sky

Ficetz formations in the North of Ireland, described

Green, in the North of Ireland, described 3 .
——-— of Ireland, fossils of P Fj - F
———— fied. See Red sandstone.
Scavig, Loch, Description of . . °
Schiefer spar, sometimes found in the lees eous beds in Gen
Tilt - : ° . : : °

Schist, of Glen Tilt, akon tees ‘ ;

singular variety of, found in Ben Gloe

Section, remarkable one shewn in the valley of the Tilt

Serpentine, noble, commonly mixed with the marbles of Scotland

Szymour, Lorp Wees. Description of a Clinometer

Shale, its thickness in the Lincolnshire Wolds : a

Sheil mirle, bed of, in Glen Tilt < F A : ?

Sxey, Joser#, MD. Physician to the Forces. Remarks upon
the Structure of Barbadoes, as connected with specimens

of its rocks : ; : , F ,
Sky, Dr. Mac Curroen’s Sketch of the Mineralogy of

—— general geographical description of °
great Northern division consists of trap °
Votre Il 3K

441

PAGE

449 INDKX.
PAGE
Sky, description of the rock districts of ; ‘ 12
—— smal] quantity of alluvial land in 18
—— description of the Coasts of : : ° . ¢ 19
—— remarkable slide of the cliffin . : : : . 22
—— detailed description of the rocks of : ‘ ; 28
—— Marble limestone alternating with shell limestone reposing
on syenite in 3 ° 4 ° E . 4]
—— account of the mineral Kiltanees ; ia Ls y : . 82
junction of trap and shale in . : : ; 99
description of the marbles at Strath in : : : 101
Slate, interstratified with limestone is bes madrepores, in
Somersetshire * . : ‘ : . 344
Sleat district in Sky, consists of mica lore : : : é 28
Slide, remarkable one of the cliff, in Sky . ° : é 22
—— of the hill in Strathaird in Sky . : - 24
—— in the conglomerate, at Mount Radford } ; . 362
—— numerous on the coast of Somersetshire 372
Somersetshire, Leonarp Horner, Esq. Sketch of the Geclopy of 338
Sphenc, found in the granite of Glen Tilt . : : : 301
Stalactites, abundant in a cave in Sky . 2 : . 26
Steatite, occurs in the trap in Sky : . . : . 91
mixed with the marble of Glen Tilt ‘ ; 283—285
Stilbite, abundant in Sky : . ° 85
Storr, in Sky, Zeolites abundant in the rary ath!) . 16
Strath, district in Sky, lies on a bed of limestone : : 7
—_— Description of s : . : . 15
Strathaird, in Sky, situation of the district so veiled 5
almost entirely composed of secondary strata 7
remarkable trap veins at. : . 79
Stratified rocks, in Sky, description of . ; 31
their contact with quartz rock and mica dite 31
Strontian, sulphate of, found crystallized in the septa of lime-
stone masses, in Somersetshire ‘ 5 i 4 371
Submarine forest, on the coast of Ss rierietanite g : : 380
Swepenstierna, C. T. An account of the Swedish Corundum
from Gellivara, in Lapland : : : . 415

INDEX.

Syenite in Sky supporting and mixed with limestone.

in Sky, described . omeiis ‘ .

—— — its tendency to decompose

——— in contact with marble limestone, in Sky

——— in Sky of later formation than the limestone

——— in the North of Ireland, described . ; 5
——.— distinguished from syenitic granite, by Dr. Mac Cis
Syeuitic granite, and granite, their Geological identity

Talc slate, mica slate passing into, in Sky x . »

Talisker, in Sky, abounds in zeolites F : ’

Tellurium, Prorrssor Esmarx’s Description die anew Ore of .

Titanium, Oxide of, found in Scotland 3 A

TraiLy, THoomas Stewart, M.D. Observations on the Salt Mines
of Cardona, made during a tour in Spain in the summer

of 1814 5 A ° ° ° °
Transition rocks, in the: North of Ireland, decanted ;
Trap, forms the great Northern division of Sky : :
—— decomposed, forms fertile soil. . : . :
—— veins in the secondary strata at Loch Slapin, in Sky,

washed away : ; . ! : ci ue

—— vein in a cave, in Sky : : - ° . .
—— general account of, in Sky : : ‘ :
—— stratified detached masses of, in Sky. ° :
—— varieties of, in Sky : P : : F 3 4
—— rarely columnar, in Sky - : i : f
—— veins in Sky, account of : 3 , ‘ 3 ;
—— —— two sets of : ‘
—— effect of the junction of the, on the ehales, in Sky
—— Mr. Aixin’s Observations on a bed of, at Birch Hill colliery
—— primitive, in the North of Ireland, described .
ee consists almost entirely of hornblende
—— transition, in the North of Ireland, described
—— Floetz, bed of, lying in conformable position between the
strata of sand in the coal formation of Ballycastle
—— —-— formation in the North of Ireland, described

443

PAGE

251
140
140
148

159
LW

AAA INDEX.

Trap tuff, in Sky 3 . % i

Tremolie, found abundantly in cha Merbhe oe Glen Tilt” %
- peculiar g eranular variety found in Glen Tilf

of Cornwall. Tue Rev. W. Grecor on

Uranium. Mr. W. Putiurrs on the Oxyd of, of Cornwall
Veins of trap, in Sky : .

- —— two sets of ee ages : . :
—— of clinkstone, in Sky : ° - : : :
—— frequency of, at Strathaird in Sky 5 t , :
Vein, of greenstone, in Glen Tilt : : :

large limestone, in the conglomerate 6s iirsensershin’
—— of sulphate of barytes, i in the limestone of Cannington Park

Wacke, balls of, contained in a calcareous vein in chalk ~~
interstratified with chalk in a conformable position. .
~ of the North of Ireland, described. : eae
Wells, in the chalk of the Lincolshire Wolds communicate with

the sea : J d 4 : s
Whin dykes, of Rahal, int ited ; y t F y
Wood Coal, occurs in the North of Ireland

Zeolites, abundant in the trap, in Sky ; t
——— resist decomposition for a long time
——— found in great quantities in the Storr, in Sky

——w— abundant in the amygdaloidal trap, in Sky f 58—188

——— description of the, in Sky
——— cubic, found in the North of Ireland

FINIS.

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