the bearing of the greatest portion is from the E. of N. to the W. of S., and the dip towards the N. of W. The laminæ are frequently vertical, often much shattered, and very thin. Whereever the chlorite schist is exposed, along its Western boundary, it is found presenting the abrupt edges of its lamina towards the greywacké. It is therefore most probable, that the fault exhibited on the coast, between Llaneilian mountain and the point, is carried directly across the Island.

The principal exceptions to the general direction of the dip are about Dulas. In the harbour, the laminæ, though much confused, dip nearly South, varying to points both to the East and West. In this case, therefore, they appear to dip from the high point of granite on the Llaneilian mountain.

From Llanrhyddlad (on the Western coast) to the Paris mountain, the average bearing is more nearly East and West than in the former case, the dip still towards the North. The cliff formed by this schist to the North of Carnel's point, presents the greatest degree of confusion and disrupture among the laminæ, Pl. XX. Sect. N. To the South their dip is by no means regular, but inclines in different directions to the horizon, always however at a very high angle. Around the point, and again on the shore to the West of Llanrhyddlad, it assumes a yellow decomposing aspect.

From Llanbabo to the South of Llanrhyddlad the appearances along the Northern line of junction are similar to those exhibited between Llaneilian and Llanfihangel. The actual junction on the coast near Monachdy is obscured by a mass of diluvium, but judging from the direction of the laminæ on the horizontal section formed by the shore, the greywacké is unconformable to the chlorite schist, and therefore presents a repetition of the facts exhibited on the Western side of Llaneilian mountain.

A few yards to the West of this junction,

the greywacké passes to an unlaminated hard rock mottled with patches and veins of white quartz, and finally assumes a green flinty character similar to that of the chlorite schist at the junction. There is a small cavern in the cliff at this point, the roof and Eastern side of which is formed of the flinty portion, but the schist is again found on its Western side. The union of the two is very evident, the flinty mass reposing upon an inclined plane of the greywacké, Pl. XVI. Fig. 7. The cavern does not resemble a hollow excavated by the action of the sea, but appears as though the upper part had been bent from the Eastern side, when in a soft state, so as to form an arch. It may probably be referred to the nature of a fault, but this explanation admits of difficulty.

On the Western side of the Llydiart mountain, there is a G.4. black shattery clay slate, the laminæ dip from the mountain at a high angle. In the road near Pentraeth their junction has been cut through to the depth of five or six feet, where they meet vertically, and each rock is broken and confused. Following their line of junction towards the North, the mica slate is seen, near Red-wharf bay, to rise from under the clay slate, and presents a smooth rounded surface without any laminar tendency. Between this and the' fine grained clay slate, is a thin bed composed of small angular fragments of slate (217.) and at the actual junction it also abounds in small fragments of quartz (218.) loosely cemented together. By one hypothesis this would be called the abraded portion of the two rocks produced by the upheaving of the mica slate. The greywacké may be traced as far South as Llanfihangel.

A confused patch of shattery clay slate, intermixed with G. 5. greywacké, is interposed between the chlorite schist and mountain lime, to the East of Llandonna. It does not attain to so great an elevation as either of the formations between which it

is situate, so that it is completely concealed at the spot where the mountain lime sets on (Pl. XX. Sect. P.) In immediate contact the chlorite schist consists of a confused talcose rock. Hardened veins of clay slate intermix with it (234-237.). G. 3. The greywacké district placed to the West of the coalmeasures, from Llangefni to the South of Bodorgon, possesses a different character from the rest (238-250.). That a portion of it consists of greywacké, is evident; but whether it belongs to the present series or to the last, or whether it be not rather a confused intermixture of both, I did not fully ascertain.

G. 1.

From Llangefni to Aberfraw, repeated instances of greywacké occur, to the East of the schist containing jasper, and interposed between this and the coal measures. The schist near the coal-measures presents its abrupt edges to them, but no actual appearance of stratification can be traced, and the indications which exist of a laminar tendency are of a very partial nature. On the N.W. of Llangefni, there is a green talcose clay slate (242.), occasionally enclosing embedded fragments (243.) and scales of mica (244.). It possesses an imperfectly laminar tendency dipping to some point towards the West. Along its Eastern termination from hence towards the North, it assumes a hardened unlaminated character. At Llangefni it passes to a green crystalline quartz rock (245-247.), which possesses faint, but undoubted, traces of globular concretions cemented in a paste of quartz. An occasional fragment of uncrystallized matter is also found embedded.

Through the centre of the Paris mountain, and in the direction of its ridge, there runs a bed of grey cherty stone (252, 253.) cutting through the schist partly hardened (254.), and the rest assuming a yellow decomposing aspect (255.), full of blebs and drusy cavities, which also occur in the chert.

The simple minerals found in the extensive and well known

copper mines situate in this mountain, are sulphurets of iron, copper (256.), and lead.-Sulphate of barytes.-Native copper in small quantities (257.), and still more rarely the sulphate of lead.

There are two patches laid down towards the East of the Map, as included in this formation. Certain points of resemblance to portions of the districts already described, seem to stamp them as members of the greywacké series. But they are found under such peculiar circumstances, that it is impossible to speak decidedly on this point.

The small patch to the South of Beaumaris is seen near the G.6. top of Red-hill, and in Lord Bulkeley's grounds, on the slope of the hill above the ferry-house. It appears to be an unstratified mass sticking upon the steep side of the chlorite schist, which rises very abruptly from hence towards Llandonna. It consists of small angular fragments and nodules of clay slate, highly pellucid quartz, and crystallized felspar, either firmly cemented together (263, 264.), or embedded in a hardened argillaceous paste (265-267.). The fracture sharp, and approaching the conchoidal. A perfectly flinty slate (268, 269.), with an irregular fracture is associated with it. The specimens bear a close resemblance to those procured between the clay slate and mica slate on the N. W. slope of the Llydiart mountain (216– 218.); differing from them only in a greater degree of compactness.

The patch which extends from Garth-ferry, about one mile, G.7. towards Cadnant, scarcely reaches above high water mark. The chlorite schist rises abruptly on the West, and forms a high ridge of rugged rocks. The rock at the base is formed of small angular fragments of quartz (270-273.) running together and passing to a compact mass, interspersed with specks of earthy felspar, and fragments of slate (274.). This is intermixed with a few irregular patches of black clay slate, and a compact mica

cious sandstone resembling those in the greywacké about Dulas. (275.) There is scarcely any trace resembling stratification, but the whole rises confusedly towards the chlorite schist.

The greywacké on the opposite coast, immediately South of Bangor, in contact with the coal-measures, seems at first sight to consist of large and small rolled pebbles, firmly embedded in a basis composed of fragments of felspar, quartz and clay slate (280-284.). Upon examination, the rude breccia thus formed is found to possess certain peculiarities of structure, which appear to throw some light upon the nature of a substance found in connection with it, and mentioned in Mr. Greenough's Geological Map of England as "a remarkable steatitic rock, associated with the old red sandstone between Carnarvon and Conway" (285, 286.).

Many of the pebbles, or rather nodules, are found to indent the surface of a contiguous nodule, as though the latter had been in a soft state, and pressed by the former. The surface of one bed, from which a nodule has been removed, is often abruptly intersected by the surface of another. The surface of the nodules are found to be impressed by the angular projections of the fragments which form its matrix. All the specimens exhibit these facts, and on the natural fracture of one of them (280.), where several contiguous nodules are cut through, they are particularly striking.

These facts admit of explanation, by supposing that the nodules are in reality rolled pebbles, which have been softened in some degree, and pressed, since they were brought together. There are, however, other circumstances which appear to destroy such an hypothesis.

The nodules themselves are found in several instances (281.) to be composed of angular, crystalline fragments, which are often sufficiently apparent towards the surface, but which form a compact and homogeneous flinty mass towards the centre,