nearly homogeneous nature of the chlorite schist, when compared with the very variable strata of the quartz rock.

In some places the chlorite schist is associated with rocks composed of heterogeneous materials confusedly aggregated (70— 94.). The schistose character is more or less destroyed, and the argillaceous basis intermixes with crystalline limestone, dolomite, C. 3. serpentine, and jasper. The largest tract of this description lies about one mile to the West of a line drawn from Llangefni to Trefdraeth. The ground is completely broken up by rugged projecting rocks. Some of these are slaty, but in general they present a hard jaspideous aspect with contorted stripes, which mark the existence of former laminæ. These intermix with homogeneous red jasper streaked and spotted with purple.

C. 4.

The width of this tract may be about one mile, and it is succeeded on the West by contorted chlorite schist, and this by the mica slate already described, which, though confused, decidedly dips from the granite.

A similar character prevails in the small detached strip of chlorite schist, which forms a ridge from Caint to Red-wharf bay, passing between Pentraeth and the Llydiart mountain. From Caint, as far North as Llanffinnan, this ridge is composed of green and red glossy talcose clay slate; but immediately North of Llanffinnan, it becomes disturbed, passes to a compact red jasper (58, 59.), and from hence to Red-wharf bay presents a series of broken elevations, composed of fragments of schist cemented by crystalline magnesian limestone, patches of which, as well as of compact limestone and jasper occur through the remainder of this district, intermixed with schistose materials. At its termination in Red-wharf bay, it forms a low but perfectly vertical cliff, facing the N.W., intermediate between red jasper and clay slate (60.), and possessing a fissile texture. Both

the common and magnesian limestone present different tints of grey, yellow, and flesh red (88-93.).

In contact, and on the steep side of one of these projecting masses of limestone, is found a calcarious tuffa (94) enclosing fragments of slate, and recent snail shells. I mention this circumstance as it may perhaps tend to shew, that some particles of this limestone have been in a state adapted to solution at no very distant period, although its present position should seem to indicate, that this action has ceased.

Fibres, resembling a coarse asbestos, penetrate the solid jasper (86.), and sometimes appear as small veins, (the fibres perpendicular to the sides) traversing a light porous mass into which the jasper passes.

At the Southern point of the promontory at Llanddwyn, C. 5. there is another partial formation of a similar nature. At one spot are numerous kernels, about the size of peas, dispersed through the schist (80, 81.). These appear to consist of a light green serpentine, in which lime predominates.

Half way between Beaumaris and Garth-ferry, in the new road, there is a rude projecting mass of rock, composed of red crystalline limestone, and jasper (83.), embedded in, and intermixed with decomposing argillaceous materials. When passing close to this, it appears to form a high projecting point of the cliff, but viewed from the river, it is seen in reality to be situate in the bottom of a gap formed by the schist rising abruptly on either side.

The clay slate, on the S.W. slope, and near the summit of Bodafon mountain, situate at the Northern termination of the c. 5. middle district, passes to a compact mass between hornstone and jasper (95-100.). It is irregularly streaked with different shades of green, dull red, and grey. It fuses to a transparent frothy white glass, and probably contains a great proportion of

felspar. Indeed the red stripes actually pass from a compact nature to crystalline veins of felspar, which are occasionally associated with stripes of white quartz. Specks of sulphuret of copper are dispersed through the mass.

Contorted patches, and strings of crystallised quartz and red felspar (121-123.), occur in several parts of the chlorite series, both among the crystalline and earthy varieties. In the M. 1. new road to Holyhead, S.E. of Llanfihangel-East*, I procured masses of crystallised felspar four inches cubed (123.). The colour varies from deep to light red; the structure is curvedlaminar passing to compact.

C. 5.

G. 1.

On Red-hill, to the South of Beaumaris, is a bed of crystalline quartz (118, 119.), which is quarried for the Staffordshire ware. Other beds of a similar nature are met with in various parts of this schist.

On the shore at Cadnant are broad veins of quartz, slightly contaminated with chlorite (120.). These veins pursue a direct course, and resemble trap dykes in external character.

A broken flinty ridge runs from the N.E. side of the Paris mountain to the S.W. of Llaneilian mountain. A fissile texture is sometimes visible, and the rock passes to a schist (111.). Its fracture and aspect vary from flinty to cherty, and its colours are different shades of light green (113, 114.), grey (115.), and red (116.). Sometimes there are small crystalline specks of quartz and felspar dispersed through the mass (117.), which give it a porphyritic aspect. It is semi-translucent on the edges and fuses to a white frothy enamel. This is, perhaps, more nearly allied to hornstone than that from Bodafon mountain.

The transition to a compact flinty or cherty mass, is found in several other portions of this district (108—110.).

* I have added "East" to the name of this place, to distinguish it from another Llanfihangel situate on the Western side of Anglesea, on the confines of the chlorite schist (c. 1.) to the S. E.

Limestone Beds.

{Nos. 124-152.}

has

Limestone, in the form of veins and small patches, already been noticed; it also exists in distinct irregular beds in several places, which are marked in the map by an L. In the cliff, East of the island on which Llangwyfan church is situate, C.3. there is a bed of compact white marble mottled with black (124, 125.).

Other beds of the same nature occur on the promontory South of Aberfraw.

Also at Gwalchmai, immediately to the S.W. of the lake. As the limestone passes into the schist, it assumes a fissile character, and scales of chlorite are dispersed over the natural fractures (127.).

A compact dark brown and grey limestone (131, 132.), not unlike some of the more crystalline varieties of mountain lime, has been quarried about Llanfacthlu to a considerable extent. C.1. There is an impure shaly substance associated with it (132.), somewhat resembling the shales of the coal measures.

Small caverns occur in this spot, the surface of which are rugged, and contain hollow cavities resembling the exposed portions of a limestone district on the sea shore. No stalactites are to be found in them.

Very considerable beds of a similar limestone extend from C. 2. Glan-y-Don to Cemmes.

In none of these beds was I able to find any trace of organic remains.

Serpentine.

{Nos. 133 to 187.}

Two districts are laid down in the map, in which the principal masses of serpentine are found. These occur in beds sub

S. 1.

S. 2..

S. 1.

ordinate to the chlorite schist, and do not form one continuous line of rock.

In the Southern district, they form a range of detached and nearly tabular masses, which extend from the N.W. of Rhoscolyn church to Llanfihangel, rising through swampy ground, and accompanied by projecting patches of schist which dip in various directions Pl. XVI. Fig. 5. The compact serpentine passes into slaty; and sometimes a tabular mass exhibits this double structure, when viewed at a short distance, Pl. XVI. Fig. 6.

The serpentine near Llanfechell is not sufficiently exposed to enable us to trace its connexion with the schist. The patches, in which it is found, have been quarried, and appear to be nearly envelloped by a hard compact variety of chlorite-schist.

The purest specimens are dark green with a semi-translucent greasy lustre (133-135.), but the general appearance is that of a compound rock, in which serpentine and dolomite form an irregular mixture (141-151). Patches of light yellow also occur (145.). A considerable portion of that which is quarried at Llanfechell, consists of very compact dolomite, tinged green (146.) or red (148.); sometimes striped (150.); in which patches of serpentine are embedded. It is here associated with common compact limestone (152.). The red tinge also pervades some of the more slaty varieties (153—155.).

Near Rhoscolyn the serpentine is associated with a heavy, compact and granular, black limestone, which does not resemble dolomite, although it will not effervesce in cold acids (161—163.).

Patches and veins of beautifully saccharine and white dolomite are dispersed through each district (159.). This occasionally exhibits a tendency to a fibrous structure (160.), which may sometimes be traced partially through several specimens of the serpentine.