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[Geological notes probably on tour with Sedgwick]

 

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(1

Langollen - Ruthvin

Saturday 6th [August 1831] Vale of Crucis. The bank facing the abbey consists of Clay slate, which breaks out at regular intervals striking NW. by N. dipping 25° to the NE by N.

At different parts of the road observed beds of diluvium very like Shrops, only no sand: also boulders of trap.

Beyond V. of Crucis. on the road to Ruthvin the Limestone is seen having a grand escarpement to the West: The contrast between this & the more regular slope of the Clay Slate gives great grandeur to the views. The Greywacke generally covered by Gorse, Heath & Fern; the limestone either bare or the verdure very green. About mile & 1/4 before the road passes Dafarn Dowarch going to Ruthven quarry of Clay slate (A) containing organic remains a sort of flattened Pecten, & about 4 miles before this the slate is quarried although it is of an inferior quality

 

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2/ About 1/2 mile beyond Daforn, a black bituminous Limestone, organic remains veined quartz in parts reddish, in one part strata exactly arched the line N by E. - 1/2 mile further a tortuous valley through Clay Slate, generally dipping to E.

About mile from Ruthvin beds of Sandstone.

= Notes from Mr. Dawson of the Limestone in Vale of Clwyd.

(1) W. bank 1/2 mile S by W of Slanganhafal dip 40° W. Not again seen for 5 miles up the valley.

(2) Graigwilt a large mass in the parish of Slanfair

(3) Above Pentre Caehelyn dip 20° W then turn round by Tynyllan fair

(4) Y Graig dip N. 17° (1 mile NE of Slaneildan)

(5) Then turns round to the N & seen on

 

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the Corwen road about 1/2 m of Slanelidan church, then a regular escarpe.: ranging N & passing 1/2 m W. of Ruthvin.

Ruthen: takes its name from the new red Sandstone on which it is built. The soil is red for some miles about the tow. & the whole plain may be considered of that formation only in most places covered up by diluvium. 1/2 a mile to the west of the town a quarry of it is worked. The rock is spotted with brown like the stone at Cardeston overlying Magnesium conglomerate, it is very irregularly stratified: but the rock on which the castle is built, is in nearly horizontal seams. Just above where this quarry is we find Limestone dipping E 15° N L 9°, fine grained, with petrifactions

 

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Under this, there are some beds of Old red Sandstone. Striking the same way as the overlying Limestone but dipping at greater angle. A little further is more clearly visible in a water course.

Aug 7. Ruthen to Denbigh. For the greatest part of the way you have the Limestone about 1/2 a mile to your left. When you come about 3 & 1/2 miles to Denbigh pass through the new red, Denbigh Castle is built on the Limestone. from which point the Limestone ranges away to the N. with few points West.

Aug. 8th. We were told that road from Denbigh to St Asaph passes through new red Sandstone. We followed the escarpement of the

 

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Limestone to the West of the road. About 1 & 1/4 from Denbigh N few points W dip NE by E. L 17 containing Sulph: Barytes Producti (3/.

At Henllan rock almost composed of Producti & Madrepores. Dip NE 1/2 N Half mile NW of Henllan Grey Wacke dipping N by E.

At Cefn grand escarpement, rock with Caverns wooded, river winding at bottom giving very much the same character to Scenery as in Derbyshire the strata dip N 25° E.

[insertion:] P. Sedgwick saw that [illeg] in the mud in a cavern. Rhinoceros bones

For about 3 miles before St Asaph, the plain has same appearance as about Denbigh & doubtless it is owing to the New Red Sandstone formation. The view from St Asaph very fine. the vale Clwyd bounded on each side by long chain of green wacke

 

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that to the North, being the most perfect. The valley indeed may be said to be bounded on the South by the Limestone which on this side is much more developed: We were struck the whole way from Langollen to this place by the almost entire absence of turf pits.

St Asaph to Abegele by Bettys at the point where the road to Bettys divides from that to Abegele a shaft was sunk for lead ore in the Limestone which contained sulph. Barytes &.…

A little further on road to Bettys, I crossed a great bed of diluvium chiefly consisting of Clay slate, & under

 

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this the Limestone ranges. But there is no very apparent escarpement for some miles: The scenery along this road very uninteresting & the soil poor, a little SW of Abegele, first saw an escarpement the rock was striking W & E. Dip to N. L 30 higher on hill, same strike but L 20. It was in such points as these where the strata have been much disturbed, that I observed the greatest number of bits of Sandstone; but in no place could I find it in Situ. Beyond Abegele, I found Limestone, dipping at usual L, about 150 feet above the level of a brook. A Valley running through the escarpement showed this low section. From several observations I am sure, the Sandstone does

 

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not crop out anywhere near Abegele. The very red colour of the soil under the escarpement, I attribute entirely to the very ferruginous clay seams, in the rock itself, & not to the supposed sandstone beneath it.

Abegele -- Very cold & excellent springs break out about the town; this I should think was owing to the strata being broken, as might be expected from this great dip; & the water coming down from this great dip; & the water coming down from the mountains between the strata would be forced upwards. In the upper beds of broken limestone observed a white powder like Chalk, covering the fragments: it is called Rock milk, & seems to be sort of Stalactite. without water of crystallization.

 

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The general dip here was N by W. about L 10. This escarpement is very remarkable from its great valleys, some 1/2 mile broad & one near Colwyn 2 miles broad. In one near Abegele, there were a great number of rounded Sandstone pebbles & some few conglomerates. About 2 w of Abegele very fine escarpement. The limestone fine grained. Dip N L 9°. The escarpement facing the South, was most remarkably covered with wild flowers, & the rock coated with Lichens. From Colwyn to L Ormes head, broad valley the bottom with bed of Clay slate diluvium about 40 feet thick. P. Sedgwick supposes these great valleys were caused by the rocks being stretched & the fact of there not being Limestone pebbles in the diluvium, seems to countenance this.

 

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where the road to Bangor passes by the Limestone again. You see it reposing on the Grey wacke. The Grey Wacke hills appear to be almost characterised in contradistinction, with those of Limestone, by the quantity of Furze growing on them. The space which separates, during most of its course, the Lime from Green wacke hills is divided into a system of two vallies, or rather one great valley with a bank running up the centre, at Abegele 1/4 mile from town a pit of Sand. Most likely Alluvium, alternations of sand & fine gravel.

[missing word?] a hill lying S by W of Conway the top part very craggy consisting of quartzose greenstone, sometime porphyritic with crystals of quartz & feldspar

 

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with a prismatic cleavage. on the NW side of hill within 20 yrd of this trap, there is an indurated rotten slate, with cleavage striking NE by E. also a hard quartzose conglomerate. On the top of Penmaen Mawer a greenstone which chinks very much & runs N by W. at the lower part of this hill like the former there is an altered Clay slate at the bottom rock very like Grey Wacke. The coloured seams in the rock P. Sedgwick remarks generally indicate the strata. Through this rock there often runs veins of quartz & hornblende, & at about 2 miles to the NW. of the great Slate quarry contains a good deal of arsenical copper, which is worked somewhere near the Quarry.

Four observations on the broad (over mountain from Aber to Slate Quarry, the dip of

 

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these altered slates was SE by E.

Great Slate quarry 200 yd deep 12 workings 16 yd each thick. The rock is divided into cleavages, joints & dip. Cleavage is NE 1/2 E L 80. The joints slip from S, & hang to the

North. The dip very obscure SE 50°. Some hard chloritic quartzose veins run through the quarry & accompany the slate to Lamberris. There veins contain Carb. of Lime Quartz. Chlorite. Talc. Molybdene There are 2 principal ones. (1) has same range & L as cleavage of slate & is (including the altered slate) 2 yd thick: (2) runs N 3 W & is 7 yd thick, 4 yd being altered slate.

The vein has an appearance like this [sketch] the contracted parts abounding with quartz. The miners give the following names to the slates of different quality. 1: Queens. Dutchesses. Countesses. Ladies, & halfs. (? is this owing to their cracked character). Sedgwick says there are same names in Cumberland.

 

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Cwlm Idwal consists in a circle of steep rocks surrounding the Llyn they generally consist of an altered slate, which is very tough, of a light green colour, sometime passing into a very compact conglomerate, occasionally having an amygdaloid (owing to organic remains?) appearance: the parts which are weathered, become converted into a very rotten slate. The general cleavage is E by N & S by W dipping to the W 2 N. Many of the planes of cleavage are covered with quartz containing fibres of Titanium. This rock in many parts has a tendency to split into prismatic forms, & chinks under the hammer, in general appearance it resembles a basalt. But what is very important it contains organic remains, both in the hard light green & the conglomerate. I found Madrepores

 

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to the South of the lake there is a very large mass of Basalt protruded out of the Slate. In shape it must be an inverted cone as a section has the appearance of lapping over the slate. The Junction on each side is most clear. The basalt is a compact rather brittle, black rock, splitting with conchoidal fracture. The whole mass is more or less divided into 4, 5, or 6 sided pillars, & each pillar appears to be jointed, about a foot apart. A natural surface where the pillars end appears like tesselated pavement. The basalt appears to have carried with a large bed of the altered slate. At the entrance to Llyn Idwal is a quarry for Hone slates:

 

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Moel Shiabred. May be described as consisting of three parts. I will describe the formations as seen in ascending from the Eastern end of the Capel Curig lakes. 1st a rock like a coarse quartzose Grey Wacke, becoming alternately Porphyritic & conglomerate, with pebbles of porphyry & a compact greenish slate; proceeding higher a Feldspathic rock with veins of quartz & Chlorite. At this point there appears a line or rather a valley of separation. it is about half way in the mountain. After this the whole northern side of mountain is composed of a blue slate: the lower part almost is made of Terebratulae; the higher parts are more indurated, but cavities of a rusty substance appear to be remains of fossils.

 

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The general cleavage is W 3 S, E 3 N which is also that of the 1st part of mountain & indeed in this. there are signs Organic remains.

The 3rd part of mountain or the top is of a crystalline grey coloured Trap, with its usual cleavage -- this forms a precipice to the South & composes all that side of the mountain. The line of disturbance seems to have run NE-SW. At the Western end of hill, the Slate appears to overlie the Trap.

The beds composing N 1 of mountain appear to Dip E 2 S, & in general looks seems of different formation to main mass of mountain.

 

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South of Shiabed. Trap, slate & a Feldspathic rock alternating, nearer the mountain most trap & the more remote the slate is most abundant. The feldspathic rock appears evidently merely slate altered. These alternations last for about 2 miles S of Shiabed. General line of violence as before SW & NE. Cleavage of slate W 2 S.

Dolyddelan. A slate quarry apparently situated between the Felspathic altered rock, with cleavage W 1 & 1/2 S. From this to Moelwyn generally slate occasionally beds of Trap. Northern Moelwyn. Eastern side of it a blue slate cleaving & line of violence SW. Dip N. Carreg y fran slate NW side to the S a precipice of are hard altered compact

 

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quartzose greenish rock; it occasionally splits into column like basalt -- sometime become a coarse, but extremely hard breccia pebbles of a rock like itself. Associated with this a rock oftentimes nearly pure quartz.

Festineog. The country has the appearance of a Greywacke, so has the slate in external appearances

Drus Ardidy to the East micaceous slate; the rocks that compose the hill through which the road passes, are of a most complicated nature. generally porphyritic, with Quartz & sometimes Feldspar, & Pyrites base chiefly quartz with Hornblende & mica. The rock becomes

 

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either conglomerate or concretionary with quartz. The general dip W 3 N, but the formation of the valley appears to me to have altered it on the S side. The pass seems to be caused by a subsidence & crack of SE part strata.

For the hill on NE side would have been much loftier than the other owing to the dip, if it had not been altered by some subsidence the general appearance of valley countenances this idea. At W end of valley the rock is jointed with such remarkable regularity, as to give the appearance

 

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of beds dipping to S by W. But road to Barmouth crosses several alternations of micaceous slate, the porphyry & a porphyritic slate, with a vertical cleavage, running N & S, but one of the beds of porphyry has the apparent dip to S by W, & which if a true dip would have cut through the beds of slate which is absurd ∴ not true dip.

 

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(n) Blistered Road oxide of Iron in small quantities.

(0) soft sandstone turned or spotted yellow free from calcareous K. a Quatron rock

(n) Basis from red sand cements with hard rocks by calcareous heath. Main substance of glomacts in a [illeg] has [illeg] very slowly in Muriate acid. Spl….. before Blow pipe of a yellowish pearly colour – effervescing little but almost entirely soluble

Cartus lined often with crystals of peat & calcareous spar.

sometimes speck of Manganese

The amygdaloid sometimes is so closely

 

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united as so basin to be seen.

Basis sometimes marly:

Crystals of pearls spar very brown: inbedding numerous round pebbles of granite & occasionally dark red sandstone

Cavities generally almond shaped sometimes angular, cells flatten

2 remarkable specimen (1) a piece of Limestone. (now nowhere) a mass circular end propels out from sometimes decomposition longer

(In/ more basis

(2) a piece of [illeg] corroded as I have observed [2 words illeg] as if eaten into [illeg] hole by some shell. 

 

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