The South Staffordshire Coalfield/Chapter 4

by Joseph Beete Jukes

CHAPTER IV.

Description of the Rocks—continued.

3. The Permian Rocks, or Lower Red Sandstone.

If the survey had been confined to the immediate neighbourhood of the South Staffordshire coal-field it would have been impossible to have obtained sufficient evidence for establishing a boundary between the New red and the Lower red sandstone. In North Staffordshire, however, better sections exist, and my colleague. Mr. Hull, in examining that district, was enabled to acquire a knowledge of the characteristic distinctions of the two formations, which he afterwards brought to bear on the examination of our district. Professor Ramsay having visited North Staffordshire with Mr. Hull, afterwards went over part of the South Staffordshire district with Mr. Hull and myself. The description of this formation, therefore, must be taken as the result of our joint labours.

It is as well to premise that the lithological distinctions between the rocks of this formation and those of the New red sandstone are often rather vague and sometimes but small. This is more especially true with respect to the second or Waterstone subdivision of the New red sandstone, the dark brown or pale red sandstones of which, with their interstratified marls and calcareous bands, are scarcely distinguishable by any lithological characters from similar beds in the Permian formation. There are, however, we believe, no brick-red sandstones like that of the Bunter, and scarcely any quartzose conglomerate to be found in the Permian formation; whenever, therefore, we get the above-named doubtful beds in our district, we can determine their geological horizon simply by their place with regard to the soft red and mottled sandstones and quartzose conglomerates. There are two parts of the district from the examination of which it is possible to arrive at a tolerably complete notion of the structure and sequence of the Permian rocks, namely, the country about the Lickey and Clent Hills, and the neighbourhood of West Bromwich.

The country about the Lickey and Clent Hills.—The south end of the Lickey Hill, that on which the obelisk stands, is composed of the quartzose conglomerates and red sandstone, believed to be there the base of the New red. On the northern end of the Lickey, about Square Coppice, as also on all the summits of the high ground of Segban, Romsley, Frankley Beeches, and the higher parts of the Clent Hills, where we get what appear to be the highest of the Permian beds in their respective localities, we find these beds to consist of a remarkable trappean breccia. This breccia is principally made up of angular fragments of trappean rocks, but almost equally angular fragments of many other rocks are found in it. A good section of this trappean breccia is shown in a road cutting just north of the brook in the lane leading from the Bell Inn, at Northfield, to Bangham Pit. The matrix of the breccia is here a brown sandstone, in places calcareous, interstratified with thin bands of marl. The imbedded fragments, some of which are slightly rounded, but the majority remarkably angular, vary in size from mere grains to blocks a foot or a foot and a half in diameter; they consist of porphyritic trap in many varieties (but no basalt or greenstone) of sandstone of various kinds, of quartz-rock, and of Silurian limestone and sandstone, some of which is certainly Llandovery sandstone, not at all altered. There are slabs of these Silurian limestones and sandstones at least 1 foot to 1½ foot square and 5 or 6 inches thick, with their edges scarcely at all rounded. The whole mass has a well-stratified character, and in some places is firmly compacted together by carbonate of lime, but in others is more or less incoherent. The slabs of Llandovery sandstone are now easily split into thinner flags by a very slight blow, and some of them seem to be already so separated in the ground. This, together with their angular character, inclines me to believe that they have not travelled many yards from their original site, and that a boss, or peak, or ridge of the Silurian sandstone lies concealed under the Permian rocks somewhere close by.

The following rough sketch (see Fig. 3), drawn to scale with a measuring tape, will give an idea of the mode of occurrence of these breccias as seen in the bank of the lane above spoken of.

Fig. 3.

Diagrammatic sketch of the Permian sandstone and breccia in the bank of the lane leading from the Bell Inn, Northfield, to Bangham pit. Length of sketch about 80 yards.

A. Coarse sandstone and conglomerate, containing large angular blocks and slabs of shelly sandstone, from 16 to 18 inches long, and 4 to 6 inches thick.

B. Fine sandstone, sometimes containing pebbles and smaller angular fragments.

C. Hard, very regularly stratified breccia of flat angular fragments.

D. Bed of red or brown marl.

In the Clent Hills the breccia has a red marly base, and is chiefly made up of large and small angular fragments of a dull red felstone porphyry, often much decomposed, and splitting, when struck with the hammer, along concealed joints, so as to expose no fresh fracture; of fragments of greenstone; of one or two kinds of sandstone; "with several fragments of a porcelanic-looking slaty rock, like some of those west of the Stiperstones. Near St. Kenelm's chapel this breccia passes down into 1, red marl, with small brecciated fragments at the top; 2, red standstone; 3, red marl; 4, calcareous sandy rock."^[1]

On Romsley Hill, going down into Hunnington, just below the trappean breccia, was found a dull brown sandstone, with a band of calcareous concretionary sandstone. Near a place called Newtown, about a mile to the east of that, are quarries where a similar concretionary calcareous sandstone (a regular cornstone) has even recently been burnt for lime. In going down the brooks from this point to Twylands and Cooks Woods, we get numerous alternations of brown, or brownish grey, or purple, or pale salmon-coloured sandstones, sometimes thick-bedded, sometimes flaggy, with beds of marl, either dark purple with light-coloured spots or blood-red. Many of the sandstones are calcareous and concretionary, and might be mistaken for some of the cornstones of the Old red. A dark purple sandstone, with minute white specks, is a characteristic bed. All these beds are apparently horizontal, being successively exposed only by the rapid fall of the ground; and near the bottom of the slope the blueish grey sandstones and shales of the coal-measures appear from underneath them, likewise in a horizontal position.

The neighbourhood of West Bromwich.—In the cutting of the Birmingham and Dudley railway, south of Sandwell Park, were seen rising to the west, from under a thick mass of quartzose conglomerate, a series of brown and pale sandstones, with merely a few small and slightly angular pebbles. In these beds are masses, believed to be in situ, of a singular calcareous conglomerate that is better shown in other places. Under them, we have other pale sandstones alternating with bright red marls, all rising to the westward at an angle of about 10°. We have an account of a boring made hereabouts near "The Ruck of Stones," some years ago, by Mr. J. W. Unett (see Vertical Sections, sheet 18. No. 27), consisting entirely of alternations of red, brown, and grey sandstones of various degrees of hardness, with many beds of red marl, mottled clunch, and other similar materials, all evidently belonging to the formation we are now describing. The depth of the boring was 221 yards 1 foot, or 664 feet.

Nearly a mile west of this, and therefore commencing in much lower beds than are seen in the railway cutting, we have several deep coal pits, the most remarkable of which are those formerly sunk by Messrs. Davis at Bullocks farm, near Spon-lane (sec Vertical Sections, sheet 18. No. 28). In these pits they passed through a mass of sandstones and marls belonging to this formation, 262 yards 2 feet, or 728 feet thick, or, deducting the odd 28 feet for surface drift, &c., 700 feet of Permian, a good part of which at all events, if not the whole, must be below the 660 feet passed through at the "Ruck of Stones." What makes the section of these pits most remarkable, however, is that there occurred in them a small seam of true Permian coal. The following is an abstract of the upper part of the section:—

		FT.	IN.
1.	Sand, &c.	28	6
2.	Alternations of red sandstone with red and mottled marls and clays	169	0
3.	Fire-clay	3	0
4.	White binds	12	0
5.	Little coal	0	10
6.	Fire-clay	3	8
7.	Red clay and sandstone	28	0
8.	Dark and pale red sandstones	213	6
9.	Alternations of red and white sandstone, with red , and mottled clays and marls	270	0
		727	6

I saw masses of the fire-clays Nos. 3 and 6 on the pit bank while these pits were being sunk, and they did not differ either in colour or in any mineral character from the fire-clays of the coal-measures, except in having small] calcareous nodules interspersed through them. These nodules were carefully searched for fossils, but none were discovered. In the red sandstones below, however, numerous rough casts of the large stems of plants, something like rude sigillariæ occurred.^[2] Part of the 10-inch coal was shaly and rotten, but about two inches of it is a beautifully bright coal, highly bituminous, very brittle, with curious circular concentric concretionary markings,

At Lord Dartmouth's pits at West Bromwich Heath, there appears to be 268 yards 2 feet, or 806 feet of Permian rocks, alternations of red sandstone and marl, but without any grey fire-clay and coal. At the Lyng colliery there was 550 feet, at the Lewisham pits 315 feet, and at the Terrace pits, close to the fault, they had 135 feet of "red rock" (see Horizontal Sections, sheet 25. No. 7).

It appears, then, that there must be in the neighbourhood of West Bromwich a total thickness of 1,500 fect at the very least, composed of the rocks of this formation.

I have yet to describe the calcareous conglomerate mentioned above. This is well shown at Barnford Hill, two miles south of Oldbury, and thence to Brand Hall. It is composed almost entirely of rounded and semi-rounded fragments of mountain limestone and chert, with some pebbles of sandstone that may be millstone grit. It is about 20 feet thick, and is in several places quarried and the limestone pebbles burnt for lime. It occurs again in a field opposite the Gough's Arms, at Great Barr, as also in Baggeridge woods on the west side of the coal-field.

Besides this calcareous conglomerate, many of the sandstones sank through in the pits, or exposed in the quarries and cuttings, are very calcareous, like those before described in the district south of the coal-fields.

The reader must be pleased to bear in mind, that these descriptions of the Permian and New red sandstone rocks are meant to apply solely to the district of the South Staffordshire coal-field and its immediate neighbourhood. The Permian rocks of the neighbourhood are believed to be variable, both in lithological character and in thickness, with perhaps many frequently recurring characteristics, but no uniformity. The thickness of the formation is believed to vary almost indefinitely within the limits of 1,000 or 3,000 feet.

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Professor Ramsay, in his paper on the Permian breccias in the Geological Journal,^[3] gives a more full and complete account of them than is contained in the above brief observations, and takes a different view as to their origin. He first of all describes those about Enville, where the Permian rocks are largely developed. The breccias there consists of "angular or sub-angular" fragments, "with flattened sides and but slightly rounded edges," embedded in "a deep red hardened marly paste. The pieces collected consist chiefly of fragments of micaceous schist, micaceous sandstone, quartz rock, grey sandstone, chert, purple grit, green sandy slate (one of them polished and scratched), black slate, altered slate, greenstone, felstone, felspathic ash, and reddish eyenite. The last is doubtful. A nodule of ironstone was also observed, and a few quartz pebbles. None of them are larger than 6 or 8 inches in diameter."

He then describes the breccia of the Clent Hills in the following terms:—

"The breccia here consists of pieces of various rock embedded in a hardened red marly paste. Like those near Enville, they are generally angular, or have their edges but slightly rounded. Their sides are often flattened, sometimes polished, and occasionally scratched. They rarely exceed a foot in diameter. On Clent Hill the fragments consist of felstone porphyry, greenstone porphyry, greenstone amygdaloid, ribboned slate, black and green slate, red sandstone, quartz conglomerate, and felspathic ash. In a section near Romsley stones of the same nature were found, including altered sandstone, conglomeritic ash, banded felspathic ash, quartz rock, variegated marl, quartz pebbles, altered slate, ribboned slate, and blocks of a coarse conglomerate.

"The igneous rocks of Staffordshire are very different from those in the breccia; and none of the other kinds quoted occur in that district, with the exception, perhaps, of the quartz rock, which might be compared to that of the Lickey."

Professor Ramsay then goes on to show reasons why even the quartz rock fragments are not derived from the Lickey, but as the facts mentioned by him will, in my opinion, admit of a rather different interpretation to that which he gives them. I proceed to his description of the breccia near Northfield.

"The summit of the hill, called Frankley Beeches, is crowned by an outlier of the breccia; and it also forms a piece of ground about a mile and a half long, a little to the north-west of Northfield, a good section^[4] of which occurs in the lane leading from Northfield to Bangham pit. The larger stones lie mostly at the top. Many of them consist of Caradoc limestone (Upper Caradoc^[5] of some geologists), and calcareous sandstone and conglomerate, some of them attaining a diameter of about two feet. I submitted a collection of the fossiliferous pieces to Mr. Salter, who determined the following species:—

• "Strophomena compressa.
• Orthis calligramma.
• Atrypa reticularis (very common).
• Spirifera trapezoidalis.
• Leptena (Strophomena) depressa.
• L. transversalis.
• Rhynchonella semisulcata.
• Pentamerus oblongus (rare and small).
• P. undatus.
• P. lens.
• Mytilus mytilimeris.
• Encrinurus punctatus.
• Favosites alveolaris.
• Petraia bina.
• P. subduplicata.
• Heliolites interstinctus.
• Scalites (Raphistoma) lenticularis.
• Euomphalus funatus (var. sculptus).
• Goniophora cymbeformis.
• Serpulites.

"Besides the blocks containing these fossils, the breccia includes fragments of other calcareous sandstone, ribboned slate like that near Shelve, quartz rock, porphyritic felspathic ash, felstone and greenstone like that of the Lower Silurian rocks, purple conglomerates similar to those of the Longmynd, and yellow sandstone and black chert, the latter like that of the Carboniferous limestone.

"The Upper Caradoc (Llandovery) limestone and fragments of calcareous sandstone and conglomerate are peculiar. They do not resemble the Caradoc beds of Walsall, Builth, Malvern, Mayhill, or the Lickey; but both lithologically and zoologically they are like the equivalent strata that rest unconformably on and once formed the beaches surrounding the Longmynd and adjacent Lower Silurian rocks, where in situ they contain green and purple slaty fragments and pieces of felspathic trap, derived from the waste of that ancient Cambrian and Lower Silurian island. They may be identified by this circumstance, for in no other place with which we are acquainted does the Upper Caradoc assume this character; and Mr. Salter also gives the confirmatory opinion that the assemblage of fossils nearly resembles some of the groupings in the present rocks near Hope. It is, therefore, difficult to escape from the conclusion that the rocks generally must have travelled from that country across a space of from forty to fifty miles."

As I had no personal acquaintance with the Llandovery rocks on the flanks of the Longmynd, near Church Stretton. I failed to recognize the fragments of slate and other rocks which were found by my friend and colleague in the pieces near Northfield until I saw his collection in Jermyn Street, and many of the pieces certainly appeared to me, as before stated, very like the sandstones near Barr, and the pieces which were formerly to be seen lying on the old pit banks north of the Colmers near the Lickey.

Professor Ramsay then describes other localities where this Permian breccia appears, between the Forest of Wyre and the south end of the Malvern Hills. One of these localities, called Church Hill, nearly half way between Stourport and the Titterstone Clee Hill, is very remarkable, since it forms an outher of the breccia resting upon and entirely surrounded by Coal-measures. Professor Ramsay shows that these breccias extend altogether over an area of not less than 500 square miles,^[6] and points to the fact that the great majority of the angular fragments seem to be all derived from the neighbourhood of the Longmynd near Church Stretton.

He arrives at the conclusion, from this great extension of the breccia, from the size (up to three-quarters of a ton) and angularity of the embedded fragments, and from the polished and grooved and striated surfaces of some of them, that they were transported and deposited by the same agency as the boulders in the boulder clay of the Pleistocene or Glacial Period, namely, by the action of glaciers, and icebergs or shore ice and ice floes.

As the action of glaciers is a subject to which my colleague has paid so much more attention than I have, his opinion is entitled to much more weight on the point than any I could give, and I therefore would draw the reader's attention to Professor Ramsay's explanation of the origin of this breccia, in opposition to the conclusion that I myself arrived at, that the fragments might be derived from adjacent rocks now concealed under the Permian and New red sandstone of the neighbourhood.

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1. Professor Ramsay's MS. Notes.
2. These large stems of plants, as also the pale sandstone in which they lay, were exactly similar to those got by Professor Sedgwick from the Lower red sandstone under the Magnesian limestone in the county of Durham, specimens of which are in the Woodwardian Museum at Cambridge.
3. On the occurrence of angular, sub-angular, polished, and striated fragments and boulders in the Permian breccia of Shropshire. Worcestershire, &c., and on the probable existence of glaciers and icebergs in the Permian epoch, by Andrew C. Ramsay, F.R.S., F.G.S., Geol. Journal, vol. ii,. p. 185.
4. This is the section drawn in Figure No. 3.
5. Now called Llandovery sandstone.
6. See also his lecture to the Royal Institution. April 24, 1857.