Arthur Aikin

“ Of the former variety the most abundant is the common nodular agate, or Scotch pebble. In these the central nucleus and other parts composed of pure quartz are unaltered, the flesh-coloured zones, consisting of silex and red oxid of iron, have become more or less adherent to the tongue, have nearly lost their lustre, and have had their hardness much impaired; while the milk-white zones which in the perfect state of the substance were of pure chalcedony, are in every instance reduced to an opake white earth, yielding generally to the nail, and strongly adherent to the tongue. ”

“ The die-earth, or dead earth as it is also called, is a name given by the miners to this bed as indicative of the fact that from hence downwards all the coal strata die or cease. Its colour is greyish; and it consists of fine sand, of particles of limestone, and of clay, mixed together in very various proportions; it is often also micaceous. It has sometimes a strong tendency to a slaty structure and a stratified arrangement, with which also the direction of the spangles of mica that it contains for the most part corresponds. ”

“ None of the beds are known to vary materially in thickness except the trap. The thickness of this latter in the Engine pit and in the Bye pit amounts to 24 feet, but in the pit B it is diminished to 12 feet, and in the pit D which is sunk down to the third coal the trap is wholly wanting. The miners themselves conclude from these facts, and apparently with reason, that the bed of trap is merely a great wedge from the green-rock fault which has intruded itself between the proper coal strata, but is by no means co-extensive with them. ”

“ In some parts there is a saalbande or sticking of grey clay an inch or two in thickness, and here the vein is the least productive; in other parts the rock is hardened by an infiltration of quartz, and these are uniformly found to be the most productive. There is no regularity in the arrangement of the contents of the vein, but generally the galena occupies the sides, and the sparry veinstones the centre. ”

“ The sandstones which make part of the first thirty strata, are fine grained, considerably micaceous, and often contain thin plates or minute fragments of coal. The thirty-first and thirty-third strata are coarse-grained sandstone entirely penetrated by petroleum; they are, both together, fifteen feet and a half thick, and have a bed of sandy slate-clay about four feet thick interposed between them. These strata are interesting, as furnishing the supply of petroleum that issues from the tar-spring at Coalport. ”

“ The colour of the rock where it has not undergone decomposition, is bluish or greyish black, probably from a mixture of carbon, for by exposure to the air it passes to a pale yellowish-grey, with a few spots of oxide of iron. ”

“ The pebbles of quartz, which are numerous, appear to have undergone no change whatever.
The pebbles of limestone are the most abundant of all, and have undergone considerable change. The madrepores and other coralloidal bodies of which the limestone is principally composed, resist the solvent action of the water which percolates through the sand much better than the compact calcareous matter that is interposed between them does; the same is the case with the slender veins of calcareous spar by which the limestone is traversed ”

“ Of this greenstone there are several varieties. Sometimes it is of a dark bluish-green colour, passing into iron-grey; is massive, glimmering, of a coarse-grained uneven fracture, and breaks into irregular rather blunt-edged fragments; it gives a pale greenish-grey streak, is considerably heavy and difficultly frangible. When immersed in an acid an effervescence is perceived from various parts of its surface: by examination with a lens it appears to be composed of hornblende and felspar, with a little calcareous spar and mica. ”

“ The indurated sandstone is of a yellowish grey colour, dense, compact and ponderous; it consists essentially of fine grains of quartzy sand and silvery mica, and contains very slender imperfect veins of calcareous spar, and small irregular granular concretions of ferriferous carbonate of lime: these concretions decompose by exposure to the air, and give the external surface of the stone a brownish yellow ochry tinge. ”

“ The independent coal-formation is found immediately adjacent to the red sandstone from Wombridge in the parallel of Wellington to Coal-port on the Severn, a length of about six miles; its greatest breadth is about two miles. It rises west a little to the north at an angle of about 6°. It is composed of the usual members, namely, of quartzose sandstone, of indurated clay, of clay-porphyry, of slaty-clay, and of coal, alternating with each other without much regularity, except that each bed of coal is always immediately covered by indurated or slaty-clay and not by sandstone. ”

“ The upper beds, or rather the superficial parts of many of the beds, are in the state of shale, that is, they are shattery, soft, and more or less decomposed. No true veins ever occur in this shale, and even veins of considerable size and regularity in the compact part of the rock, terminate almost immediately on coming in contact with the looser part. ”

“ The moisture contained in the bed is primarily rain water, and it is not easy to see what active agent it can become charged with in draining into the interior of the mass, except carbonic acid or carbonate of lime: any of the stronger acids, such as the sulphuric, resulting from the decomposition of pyrites, would immediately be neutralized by the calcareous matter in which the whole bed abounds. Alternations of moisture and dryness, of heat and cold, to which the decomposition of the exposed surfaces of rocks is so generally attributed, could have little or no influence in this case ”

“ The general cultivation of the surface of this hill is a great obstruction to minute research, a difficulty that fortunately does not apply to the other great deposit at Steeraway, where an excellent opportunity of observation is afforded by the limestone quarries at that place. ”

“ The slaty clay, with subordinate beds of ironstone, which lies above the greenstone, differs but little from the common slaty clay of the coal formation. This however is by no means the case with the three beds that lie immediately below the greenstone, namely, the indurated sandstone, the carbonaceous slaty clay, and the blind coal. ”

“ The colour of the witherite is white with the slightest possible, if any, tinge of yellow: its fracture is broad striated approaching to strait-foliated: it is for the most part massive. I have seen only a single specimen that presented any indications of a regular crystalline form. In other particulars it agrees with the usual descriptions of this substance.
The Anglesark witherite has been analysed by Klaproth, and besides carbonate of barytes appears to contain above two per cent. of carbonate of strontites, and a scarcely appreciable quantity of oxide of copper. ”

“ The beds on each side of the central fault rise nearly S. at an angle of about 6°; but, in the immediate vicinity of the green-rock fault, the second coal and all the beds lying above it (as far as they have been explored) are thrown up at an angle so rapidly increasing as, in the space of about 100 yards, to amount to 25°. ”

“ That the Viger coal, with its superincumbent clay, occupies thickness of about twelve feet at Madeley, is diminished to three feet at Lightmoor, and is entirely wanting in all the collieries which lie to the north of the latter. That a bed of clay, usually known by the name of the upper clunches, bears a thickness of from fifteen to twenty-six feet in all the above mentioned collieries, except that of Ketley, where it is entirely wanting.
The rock upon which the coal formation rests, is either die-earth or limestone. ”

“ Riders, or ribs of rock inclosed within the vein occur, but not frequently. The ore is for the most part foliated galena and striated galena, called by the miners pot ore and steel ore: iron pyrites is the next in quantity, and lastly blende, this latter being for the most part so intimately mixed with the galena as to be scarcely visible. The veinstones are calcareous spar, often approaching to schiefer spar, and foliated heavy-spar (called here water spar, because from the looseness of its aggregation most of the water drains through it into the mine.) Quartz is more rarely met with ”

“ The first coal forms the ninth bed from the surface, at the depth of one hundred and two feet, and is not more than four inches thick: it is very sulphurous. In the space between this and three hundred and ninety-six feet, lie nine other beds of stinking coal, none of which exceeds the thickness of seven inches except the lowest, which is a little more than a foot and a half thick. The first bed that is worked is a live-foot coal at the depth of four hundred and ninety feet, between which and the big-flint sandstone, already mentioned, are a ten-inch and a yard coal. ”

“ The principal argument in favour of motion by depression, is the absence of any unstratified rock between the elevated stratum and that which naturally lies below and in contact with it; to which may be added the fracture and disturbance of those superincumbent beds which lie on the dip of the elevated stratum. ”

“ Beneath the quartz-grit lies a very extensive bed of claystone or compact felspar (for it presents the characters of both these minerals in different places, and even occasionally passes into jasper) . Sometimes it is very distinctly slaty and stratified, which is particularly the case with the lowest part of the bed, which rests on greenstone and amygdaloid, and occasionally exerts a pretty strong action on the magnetic needle. The craggy eastern side, both of the Wrekin and of Caer Caradoc, consists of the slaty variety of this rock in nearly vertical strata ”

“ Detached lumps of galena are often found on the surface, and a few small veins of the same mineral have been traced in various parts, but chiefly near the southern extremity of the range; cavities lined with and occasionally full of petroleum occur at the northern extremity, where it comes in contact with the coal-formation. The names of the hills constituting this tract of limestone are, Mochtre Forest on the borders of Herefordshire, Norton Walls, Feifton Forest, Munslow Hill, Mogg Forest, Benthal Edge, and Lincoln Hill. ”

“ The Staffordshire strata dip rapidly towards it in a western direction, while those of Shropshire decline towards it, at a lower angle, in an eastern direction. Whether they actually past under the sandstone, or terminate abruptly on coming in contact with it, has not yet been demonstrated; many intelligent miners are of the former opinion: but to me, the latter appears the more probable, from an observation that was made a few years ago in Welbach colliery near Shrewsbury. In this coal-field, as in the two before mentioned, the strata dip towards the sandstone ”

“ Under the claystone occurs an unstratified trap-formation which constitutes the great mass of the Wrekin, the Lawley, Caer Caradoc, Ragleath and Hope Bowdler hills, the various component parts of which will be best understood by arranging them under the general heads of felspar rocks and greenstone rocks. ”

“ Besides vegetable impressions, it contains a few shells; small mytili in particular are found in the iron ore, called crawstone, which lies immediately above the little flint. One of the most remarkable beds of this clay is called the pinny' or penny-measure. It is the sixty-third in number, lying the next below the big flint, and occurs at the depth of five hundred and eighty feet. Its thickness in Madeley colliery is scarcely seven feet, but at Ketley is full twenty-seven feet ”

“ They are also much more closely accumulated on each other, and are generally elevated at a higher angle, as they advance from the south to the north: thus, the same succession of strata, which occupies a line of between four and five miles in the parallel of Caer Caradoc, is contracted within a space of less than three quarters of a mile in the parallel of the Wrekin. ”