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VOL. XL] [PART III.

PROCEEDINGS OF THE GEOLOGICAL AND POLYTECHNIC SOCIETY.

EDITED BY JAMES W. DAVIS, P.S.A., F.G.S., &c.

1890-

ON THE CHANGES OF THE LOWER CARBONIFEROUS ROCKS IN YORKSHIRE

FROM SOUTH TO NORTH. BY J. R. DAKYNS,

OF H.M. GEOLOGICAL SURVEY. In order to understand the geology of the country north of the Aire, I will first give a short sketch of the chief features presented by the Millstone Grit and Lower Carboniferous measures, as we follow the beds from to Wensleydale. In Derbyshire the Millstone Grit, as hitherto defined, consists in descending order of four or five well-marked grits, separated by shales, viz.. the so-called first or topmost grit, named also Rough rock from its coarse character ; the second grit, generally a flagstone ; the bold, well-jointed rock of Hathersage Edge and Stanedge, or the third grit; and lastly, the fourth or Kinderscout grit, which some• times consists of two beds. Below the Kinderscout grit comes a thick and variable series of sandstones and sandy shales, the " shale grit" of Farey, which has been generally called the Yoredale or Upper Yoredale grit; and then come shales in which sometimes occur siliceous sandstones, known as Yoredale Sandstones, or Lower Yoredale Grit ; then come calcareous shales; and finally the Carboniferous Limestone of unknown thickness, the upper part of which is thin-bedded and cherty, the lower massive and free from chert. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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Going northwards this type undergoes great changes ; the second grit is merely a basement bed to the Rough Rock, from which it cannot always be separated ; the third grit loses its massive character in many places ; and other beds of sandstone show themselves amid the shales overlying the Kinderscout grit. In the valley of the Coine there are four sandstones between the Rough or Sand Rock and the recognised Kinderscout grit ; the same is the case in the valley of the Yorkshire Calder ; but in the basin of the Aire the series consists in descending order of the following beds : First, the Rough Rock, which maintains throughout its usual character till it is lost to sight beneath the Permians ; seccondly, a very variable basement bed to the last, consisting generally of flag• stones. Below this comes a series of variable sandstones and shales, sometimes containing as many as fifteen or sixteen distinct beds of sandstone between the Rough Rock and the regular Kinderscout grit. This set of beds may, however, be conveniently divided into two by means of the massive grit of Hallan Hill and Earl Crag, which is continuous with the third grit of . It is this rock which, according to the mapping of Mr. Lucas, forms the well-known Brimhain Rocks, near Pateley Brig. Owing to the number of sandstones that have now come in, it is somewhat uncertain what ought to be taken as the top of the Kinder• scout grit; but there is no doubt whatever about the main mass of the bed, for it retains throughout the country its character of a very coarse and massive grit, forming crags and stacks of rock. It is underlaid by a thick but variable series of sandstones with shale partings. As there is ofttimes no definite line of separation between these beds and the Kinderscout grit, we now classify them with the millstone grit, and call them Pendle grits, because they form the chief features of that conspicuous hill. Below them lie the Black Bolland shales, at the base of which comes sometimes what Mr. Tiddeman has called the "Lower Yoredale Grit." In litho- logical character the beds of this grit answer very well to certain hard silicious sandstones of the Yoredale series, known to miners as Dirt. Pot grits. In the neighbourhood of Skipton the Kinderscout and Pendle grits are underlaid by a great thickness of shales con- Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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taining two well-marked limestones, viz., those of Eastby and of Embsay. Below the shales conies the thick limestone (800 feet seen) of Haw Bank. It is a dark thin-bedded limestone, precisely similar in character to the Thornton limestone, to which it is probably equivalent. It is extensively quarried for road metal in the Haw Bank near Skipton. The strike of the beds south of the Aire is generally N.E. and S.W., the dip increasing westward ; but about the latitude of Skipton the beds bend round so as to strike nearly east and west, with a dip of 20° to the south on Skipton Moor. An anticlinal ranges along Skibeden from Skipton to Bolton Abbey, with a steady dip to the north, and many a fold on the south. Thus the mountain limestone of Haw Bank has been brought up between two ranges of millstone grit hills, viz., Skipton Moor on the south and Embsay Moor on the north. The beds are much faulted and contorted, particularly along the south side of Skibeden. Good instances of contortion are to be seen at Draughton and Wheelam Rock Quarries, and at the Hambleton Rock Quarry : and a fine section of contorted beds is to be seen in Haltongill. The Kinderscout grit of Skipton and Draughton Moors striking east descends to the River Wharf, north of Addingham. Its high southerly dip carries it up the slope of Langbar Moor, its base running just below Beamsley Beacon. It then, under the influence of a branch of the Skipton anticlinal, plunges down northward to the Kex Beck, where the beds bend up again and rise northward to Hazlewood Moor and Bolton Park. Here, on the strike of the Skipton anticlinal, the beds bend over northward, and recross the Wharfe below Laund House. South of this, as far as Bolton Abbey, limestones and shales are seen along the river. The Pendle grits run along the slope of Skipton Moor to Fair• field Hall; and east of the Wharfe are found about Beamsley and Storriths. They have not been everywhere identified on the north side of Skibeden. The general run of the beds on this side is, how• ever, tolerably plain. A set of bold crags marks the escarpment of this Kinderscout grit along Halton and Embsay Moors, Rylstone, Burnsall, and Thorpe Fells. Beneath the western escarpment of the Kinderscout grit, the Pendle grit forms at intervals promontories on Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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the Fell side. It has not been traced further than the northern extremity" of Burnsall Fell. The Kinderscout grit lies in the shape of a synclinal trough dipping eastward ; and it thus occupies with its various members the whole extent of Burnsall Fell, Barden, and Embsay Moors. The rock is well seen along the Wharfe, particularly at the celebrated Strid in Bolton Woods. On the east of the Wharfe these grits rise up in a sort of broken dome, with a quaquaversal dip to form the summit of Barden Fell, marked by the bold crags of Simon Seat. Near these crags, at the very summit of the Fell, more than 1,450 feet above the sea, some pot holes, one of which from its size is called " the great shak," mark the presence of limestone beneath the surface. The grits may be seen in Howgill and in Fell Plantation, dipping steeply to the N.W. into the valley ; but along Skyreholme Beck they turn up and dip steeply to the S.E. From Appletreewick the grits strike north-eastward, underlaid by a mass of shale, from beneath which massive beds of white scar-forming lime• stone rise regularly with a similar strike, as far as High Crag. Here the beds abut against the Fault. The details of the lime• stone country immediately south of the fault are complicated, but the general structure is simple enough. A broad band of limestone stretches across the Wharfe from High Crag to Cracoe in the form of an anticlinal ridge, which between Cracoe and the river runs from S.W. to N.E. Along its N.W. flank we find the limestone dipping N.W., at angles of 40° beneath beds of shale having a similar dip. On the S.E. side the dip is to the S.E. ; but on this side the boun• dary seems to be partly a faulted one, as the lower grits on the flanks of Thorpe Fell are striking nearly at the limestone ; but I shall not insist upon this, as Mr. Tiddeman has recently made some dis• coveries which will throw great light on the structure of the country, and it may turn out that the above-mentioned appearance of a fault is deceptive. I shall therefore merely give a brief statement of observed facts, without drawing any inference from them. The limestone is everywhere precisely similar in external appearance to the massive thick-bedded white scar-forming limestone, which forms the main portion of the carboniferous limestone of the Yorkshire Dales, and is very fossiliferous. It forms five striking hills, more or Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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less conical, that stand out abruptly from the general level of the ground lying at the foot of the Gritstone Fell. The names of these hills are Skelterton, Butter Haw, Stebden Hill, Elbolton, and Keal Hill. On Skelterton the beds have an easterly dip. Butter Haw shows an anticlinal structure. On the north side of Stebden the beds dip N.W. at 40°, but no good dip could be got on any other part of the hill ; on the south side the limestone is disturbed, and here too the basemeut beds of the millstone grit strike at the lime• stone. As to Elbolton I found it quite impossible to make out how the beds are running ; at the foot of the hill I got dips which would imply that the hill is a dome with a quaquaversal dip : but on the hill itself I could get no dips at all; so being baffled outside I tried the inside ; for the hill is traversed by veins and pipes of galina, and entrance into the very heart of the rock is to be had by the mine adits, but I met with no better success inside than out; everywhere alike the limestone seems to be an amorphous mass. The same may be said of Keal Hill, where also I could get no dips. On the east side of the Wharfe a very good section of the lime• stone is to be seen in Skyreholme Gill. The beds flatten as we go up the gill, and at length turn over and dip north, so that we come to the top of the limestone on the north side of the anticlinal. On this side there is a bed of encrinital and cherty limestone between the main mass of limestone and the millstone grit of Fancarl Crag, which is an outlier, bounded on the north by the Craven Fault. I will now give the evidence for the position of this fault. On the west its line is plainly marked from Bordley to Threshfield by the opposition of the limestone of Malham Moor and Skirethorns Wood on the north, to grits and shales on the south of the hollow running from Bordley to Skirethorns. It was for a long time a matter of uncertainty where the fault crosses the Wharfe, but a heavy flood one winter exposed a bed of coarse grit in the river just below the Linton Stepping Stones. This gave a point on the fault. Between the Wharfe and the River Dibb the position of the limestone top is very uncertain, as the beds are quite hidden by drift; but the fault must pass north of the grit outlier on Ratlock Hill, near Thruskeld. The strong spring, whence the place takes its name, is probably on Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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the fault. In the River Dibb the position of the fault is fixed approximately just above Dowscar Nook by the fact of there being- grit in place with limestone on either side. A mile further east the position is fixed exactly by the abrupt termination of the grit of Pancarl Crag against limestone on the north ; and similarly a mile and a half further east by the end of the millstone grit escarpment at High Crag. On the north side of the Craven Fault we have, east of the River Dibb, massive white limestone, dipping north at 19° under a thin band of shale, above which comes the millstone grit of Grimwith Fell. Greenhow Hill is the dome-shaped end of this band of lime• stone, and is an anticlinal broken by the Craven Fault. Between the River Dibb and Grassington the ground is very obscure ; but the millstone grit seems to be separated from the limestone by a great thickness of shales with but poor limestone bands. At Grassington, however, the limestones swell out, so that with the exception of the Dirt Pot grits there is solid limestone from the millstone grit of Grassington Moor down to the River Wharfe. Northwards this thick limestone splits up, and finally takes on the Yoredale type. At Kettlewell upwards of 775 feet of carbon• iferous limestone are seen. This mass consists of solid limestone, forming scars, but without any interbeds of plate or sandstone. The overlying Dirt Pot grit can be distinctly traced from Grassington to Kettlewell by reason of its throwing out the water percolating the limestone above it. At New Kake vein the section is as below :— Bearing Grit. Limestone encrinital. Thin Sandstone or Shale Band. Limestone. Dirt Pot Grit. Carboniferous Limestone. Northwards the uppermost limestone runs away from the mill• stone grit, the intermediate space being occupied by plate with a thin limestone. The limestone above the Dirt Pot grit, which is here the lowest Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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of the Yoredale Beds, is that which we call the Simonstone, and which Phillip's called the Simonside Limestone. It is about 16 yards thick near Kettlewell. It is overlaid by plate, and the plate by a thick limestone, Phillips' Middle Limestone, which is about 32 yards thick near Kettlewell. Over the Middle Limestone there comes in the Providence mine a series of alternating beds of plate and limestone, upwards of 36 yards thick. There is no recognisable bed answering to the Underset or Main Limestome ; but these impor• tant beds soon make their appearance as we go north. The Main or Coverhead Limestone begins to put in a respectable appearance at Caseker, and soon swells out to an important rock, forming a plateau at the head of Coverdale with a fine escarpment towards Wharfedale. It is immediately overlaid by the Bearing grit; but northwards a set of cherty beds comes in between the pure limestone and the grit; at first, as at Coverhead, this is merely a thin chert top to the limestone, but this gradually develops into a series of cherty beds, sandstones, and shales, known as the Swaledale Black and Red Beds, and further north as the Coal Sills. East of the Wharfe the Millstone Grit Series generally consists of the following members :— Shale. Sandstone. Shale. Sandstone. Shale. The Brim ham Grits. Shale. The Shell Beds. Shale. The Upper Grit of Follifoot Ridge. Shale. The Lower Grit of Follifoot Ridge. Shale. A Thin Limestone. Kinderscout Grit in several beds. Pendle Grits, thin away north, or so coalesce with the beds above as to be inseparable from them. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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The Brimham rock consists generally of coarse grit, with some• times a flaggy base ; the shell beds are cherty sandstones full of shells. This is a very valuable set of beds, as from its peculiar character it can be readily identified, and thus affords a good horizon. The Lower Follifoot grit forms Henstone Band and the top of Meugher. In placing the top of the Kinderscout grit at the horizon of the little limestone next below the Lower Follifoot grit, I mean that it cannot be lower, though it may be higher, than that horizon. The Brimham grit is supposed to be the third grit of Lancashire ; and, according to this view, the shell beds and Follifoot grits come between the third grit and the Kinderscout grit. In Upper Wharfedale the Kinderscout grit consists of the following members :— The Red Scar Grit. Measures. Sandstone. Measures. Sandstone, of Priest Tarn, probably equals grit of Pinlow Pike. Measures. Coal 0 to 6 inches. Top Grit of Grassington Moor. Shale, with a coal, 6 to 10 inches. Bearing Grit. The Bearing Grit is so-called because the lead veins are very rich in this bed. The Red Scar Grit is a coarse felspathic grit of a red tinge, which is apt to form such conspicuous red scars that it can be recognised miles away. It often consists of two members parted by a shale band containing a coal seam. It generally has on or near its top a thin bed of peculiar limestone, which has the appearance of a tesselated pavement owing to its close jointing. It is also noteworthy that bands of calcareous sandstone occur in Gatcup, near the base of the Red Scar Grit. Similar bands have been found by Mr. J. E. Goodchild, generally underlying the rock Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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which, in Wensleydale, we identified on purely strategraphical grounds as the equivalent of the Red Scar Grit. This grit is the middle grit of Phillip's mentioned on page 65 of his Geology of the Mountain Limestone district, where he is quite right in saying that " it corresponds in position with the top grit of Penhill." In Coverdale the upper part of the grit is a white siliceous rock with rootlets, like ganister. Similar ganister like rocks with Stigmaria also occur higher in the series. The frequent occurrence of ganister above the Red Scar Grit is important, and it is worthy of note that even as far south as Derbyshire ganister beds are apt to occur about this horizon, i.e., over the Kinderscout grit. In Cover- dale these ganister beds begin to be very numerous and characteristic of the beds. The lowest millstone grit is at its outcrop throughout Wharfe- dale a coarse and massive grit; but Mr. Eddy tells me that in following the lead veins eastward in the Bearing grit the rock was found to degenerate into a mass of sandy shales and flags. At the head of Coverdale these lowest grits are in full force ; but they rapidly deteriorate down dale into a mass of sandy shales and thin poor sandstones. This change sets in immediately east of Crab Gill. A similar change in character takes place as one follows the grits down Walden. I have given above a brief sketch of the chief changes which the Lower Carboniferous Rocks of Yorkshire undergo from south to north. These may be summed up as follows :— 1. The simple fourfold division of the millstone grit prevalent in Derbyshire ceases to be applicable northward, owing to the setting in of several fresh beds of sandstone. 2. The Yoredale type of beds can hardly be said to exist south of Kettlewell. From Grassington northwards the Carboniferous Limestone becomes split up by beds of sandstone and shale; and north of Kettlewell important rocks, to wit, the Underset and Main Limestones set in, so that finally we have in Yoredale the well-known type of beds that goes by that name. 3. In the southern part of its course the Main Limestone is imme- B Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on May 2, 2015

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diately overlaid by the Millstone Grit; this begins at Lower- head merely as a thin cherty top to the limestone : but the chert gradually develops into a series of cherty beds, shales, and sandstones, known as the Black and Red Beds in Swaledale. Still further north the cherty beds change into a set of water• bearing sandstones, grits, ami shales, known as the Coal Sills, overlaid by a thin but persistent bed of limestone, known us the Little Limestone. Owing to the deterioration of the lowest Millstone Grit in Walden and Coverdale and on the flank of Penhill, it is somewhat uncertain what line should be taken further north as the Mill• stone Grit base, so as to keep to the same horizon. But in my opinion the best line (at least the most certain line) to take is the top of the cherty series and its equivalent, the Little Limestone. I am aware that lithologically this would not be a good line in some parts of Northumberland ; but then we should at all events keep to une and the same horizon. It is important to notice that the silicious grits and ganister-like beds that occur in the Millstone Grit series above the Kinder• scout grits become more pronounced northwards, so that at length they become regular ganister measures, similar to those that occur in the lower part of the .