resembling hornstone, and occasionally containing small pieces of pellucid crystalline quartz. Others are wholly formed of quartz, in different states of crystallization, or are slightly intermixed with compact felspar, The matrix also assumes the same cha

racters.

The bed and surface of each nodule, upon a recent fracture, is coated with a ferruginous or ochreous crust. This crust appears also in irregular patches dispersed through the matrix.

From these facts I am inclined to think, that the appearance of a breccia arises from a concretionary structure impressed upon the same kind of fragmental quartz rock, (intermixed with slate) as that which is found on the opposite shore, and that the steatitic rock to which allusion has been made, is a further result of a similar action. This rock consists of white quartz, partly crystalline and partly compact, formed into irregular nodules which run together, but leave several interstices between them filled with a light green talcose substance (285.). The irregular seams

which produce the nodular structure are also talcose and ferruginous. Some of the nodules, especially the more crystalline, which attain to one or two inches in diameter, are distinctly composed of irregularly concentric layers (286.). The surfaces of several of these layers are also partially coated with the talcose ingredient, which on weathering becomes detached, and leaves a hollow space between the laminæ.

The homogeneous character which the whole rock must once have possessed, is evident from the numerous veins of quartz or chlorite, which traverse it, always passing through the nodules, however small, which they happen to encounter in their course (283, 284.).

There are veins of crystalline quartz with patches composed of small fragments embedded in them (287.).

How far this rock extends to the South, I did not examine; Vol. I. Part II.

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0.5.

but between this place and Carnarvon, the rocks to the East of the coal-measures rise high and abrupt. A specimen (288.) from them, at Moel-y-don ferry, consists of a flinty mass filled with embedded fragments of crystallized felspar and quartz, resembling the internal structure of some of the concretions just described. It is traversed by numerous fissures, which separate it into small fragments, and these also are coated with the same ferruginous crust as the nodules.

As a concretionary structure was not suspected during the investigation of these rocks, it is most probable that specimens might be selected which would better illustrate the facts of the case, than those which were procured under a different impression. From Garth ferry (on the Bangor side) as far as Aber, the dark clay slate is sufficiently regular. Immediately to the South of the ferry, it reposes upon a confused mixture of hardened clay slate of various shades (276-279.), which terminates in the nodular rock, just described. It should seem then, that this is the lowest portion of the greywacké series; but the junction with the dark clay slate is on too small a scale to enable us to speak decidedly, though, as far as it is visible, the fact of superposition is sufficiently evident.

Old Red Sandstone.

{Nos. 289 to 372.}

This formation varies considerably in mineral character. It occurs as a fine red sandstone, (315-321.), along a narrow strip about half a mile in width, stretching S. W. from Dulas harbour as far as Bryngole. Even here it is intermixed with shades of green (313, 314.), and beds of a coarser description (290, 291.), (295-298.). A few other small patches of a similar sandstone are met with in other parts of Anglesea, but the more common

form is that of a coarse breccia. Between Llanfihangel and 0.1. Llanfaelog it is generally composed of angular fragments of slate, intermixed with quartz (289.); a character which prevails as far North as Gwindu. From hence to Llanerchymedd a coarser variety is found with pebbles (366.), which on the beach S. W. of Dulas harbour, form a breccia of the rudest description 0.5. (293.). The upper beds extend from Bodafon to the mountainlime on its East, and consist of a coarse grit, not to be distinguished from some grits of the coal-measures (299, 300.). About one mile and a half to the South of Bodafon, and a little 0.6. to the East of an extensive marsh in that neighbourhood, this grit reappears for a short space, rising through the limestone which dips from it in opposite directions.

The fine red sandstone round Bodafon mountain, contains o.5. small nodular concretions of carbonate of lime (320, 321.).

The strata generally bear in the same direction as the laminar tendency of the last formation, but their average dip is not so considerable. In the largest district, there is no section 0.1. sufficiently extensive, which might enable us to ascertain their nature. In several small quarries about Llechynfarwy, we meet with a laminar tendency, often thin slaty (308.), inclined at an angle of 65° towards a point 30° to the W. of N. This direction of the dip prevails throughout the remainder of the district. Numerous edges of broad strata, nearly vertical, project between Llanfaelog lake and Ceirchiog, and generally possess a slight degree of curvature towards the S.E., which gives them the appearance of having been the bases of arches gone to decay. In the greater portion of this district, the subsoil is completely choaked with large fragments of the strata, and as the black clay slate is found on the shore to the South of Llanfaelog lake, it is not improbable that the whole consists of a rapid succession of faults, which have completely dislocated the old red sand

0.5..

stone, and left but few patches which may truly be said to remain in sitû.

In the portion between Dulas harbour and Bryngole, the dip is more gradual and reversed, being about 10° towards a point 20° to the N. of E. The strata consist of broad, ill defined beds. In descending the hill to the North of Bodafon towards Dulas, the succession is-a thick bed of green and red sandstone -thin shaly red sandstone-thin beds of green sandstone, with coarse fragments of quartz and slate, and intermixed with partial beds of finer materials-and at the bottom of the valley, the stream to the South of the bridge runs over a shattery black clay slate, the laminæ much confused, but dipping upon the whole at a high angle, in a direction opposite to those of the sandstone strata: an additional reason for supposing these lamina to be wholly independent of the original order of deposition, and perhaps also for suspecting that the thin slaty beds, mentioned 0.1. in the quarries about Llechynfarway, may be of a similar description.

0.3.

0.4.

In the small isolated patch to the N. E. of Llanerchymedd, the strata dip to a point 30° to the W. of N., and are interstratified with thin seams of black clay slate: which appears to indicate a gradual transition from the greywacké to the sandstone. The termination of the strata to the East is remarkably abrupt, and forms the summit of a low ridge running to the N.E. They repose upon a rotten greywacké, confused and of a yellowish brown aspect (251.).

In the patch to the S. E. of the Paris mountain, the strata dip 50°, and run from the N. of W. to the S. of E., intersecting the former direction at a considerable angle.

It seems highly probable, that no marked separation exists between the greywacké and the old red sandstone, but that the latter merely presents an extreme case of one common formation.

The greater part of this series appears to have undergone considerable alteration since its deposition. This is particularly 0.1. the case about Llanfaelog-lake, Llanfihangel, and in the outlying masses round Llanerchymedd (322-350.). By this change both the coarse (322-330.) and fine grained (331-335.), (341, 342.) varieties assume a more compact texture, arising from an intimate union, and greater degree of crystallization, of the several ingredients. In the coarser specimens, there are traces of large pebbles and fragments (322-326.), some of which may still be detached (327.); but others have become a crystalline mass (328, 329.) passing into the body of the rock, which assumes a more uniform aspect. Towards Llanerchymedd, where the quartzose fragments predominate, the rock in some places passes to a nearly homogeneous mass of quartz (341.).

Bodafon mountain affords a remarkable instance of this 0.5. nature. Without minute investigation, it might be mistaken for an unstratified mass of quartz rock, rising abruptly through the old red sandstone. It is cleft by vertical fissures, breaks into rude shapeless blocks, and presents a barren shattered aspect, not unlike the quartz rock of Holyhead mountain. The summit is subdivided into small elevations, some of which are perfectly rounded and smooth, whilst others are as as much the reverse, jagged and splintery. The sides of the fissures which traverse the quartz, are coated with red oxide of iron (345.). The quartz has a flinty semi-crystalline aspect, and is of different shades of red, or mottled with white, grey and green (343–346.). These pass to less homogeneous varieties (347.), in which may be seen distinct traces of a finely granular structure. Others exhibit a coarser texture (349, 350.), and contain quartzose fragments, but so intimately associated with a basis of the same nature, that they cannot always be detected upon a recent fracture. On a weathered surface, however, they are left