Doncaster Scientific Society
Interesting Paper by Mr. H. Culpin.
A Survey of the District.
A meeting of the members of the Doncaster Scientific Society was held in the Science Room, in the Guild Hall Yard, on Wednesday in the last week, when there was a large attendance to hear a lecture by Mr. H. Culpin upon the Local Rocks recently exposed, which proved to be of absorbing interest, and at the same time demonstrated beyond doubt that Mr. Culpin has devoted much time and trouble in the prosecuting of scientific research in the immediate locality. He has already an enviable reputation in the Society as a member of great promise, and his lucubration’s upon a subject so immediately associated with the products with which the district abounds could not fail to be a great attraction.
In introducing the subject, Mr. Culpin said : Doncaster geologists have been favoured during the last two years with exceptional facilities for studying the local rocks. Fresh sections have been made within easy reach of the town by cuttings on the new railways, and these have been supplemented by the colliery sinkings at Bently and Brodsworth.
There have been two striking discoveries, one of which has taken place in the oldest rocks of the district, and the other in the most recent rocks. At Cadeby proofs, the first undoubted proofs, have been obtained of the existence of the existence of Upper Coal Measures in Yorkshire. At Tickhill and at Bentley, evidences have been found of an unexpected extension of the ice-sheets to which our local glacial deposits are due.
But it is not only in the Coal Measures and the glacial debris that the new railway and collieries have been of assistance. They have also furthered a closer examination of the relations of the coal measures to the Permian rocks above them. They have provided fresh sections of the beds immediately overlying the Permian. They have shown where the Bunter or variegated sands of the Triassic period occupy a valley in the Permian rocks, and they have given indications elsewhere of the subsequent removal of those sands.
Light has been thrown on the gravels which cover a great part of the Triassic area east of the town; and the position of the Sandall clay with regard to the Trias, and to the glacial material scattered here and there on the surface of the Trias, has been clearly demonstrated.
If we had before us a geological model of England, it would be seen that the oldest rocks – the Cambrian, Silurian, and the Devonian – are on the west, in the Lake District, in Wales, and in Devon and Cornwall. The newest rocks are on the east and south-east. Down the centre run the Carboniferous rocks, consisting of the Mountain Limestone, the Millstone grit and the Coal Measures.
These are very much faulted and broken. And have undergone great denudation since their upheaval. In these respects, they are very different from the later rocks, which are comparatively so little faulted and disturbed that a Lincolnshire geologist look upon a displacement of a few feet as a rarity. Contrast with such slight dislocations, the southerly Don fault which extends from Sheffield as far as, and probably beyond, Cusworth Park. At Cadeby this fault, which is only one of a series of faults in the Don Valley, shows a vertical movement of 750 feet.
Lying on both sides of the Carboniferous rocks are the Permian and the Triassic series. The Permian rocks on the east side consist chiefly of the Magnesian Limestone familiar to us all in the Warmsworth Cliffs and on Hexthorpe Flatts. Above these are the Bunter sands of the Trias on which Doncaster is built.
Our geological model is one which can be stripped by taking off the newer rocks. Before doing this we observe that the Pennine Range stands out as a long wide north and south ridge, and that as we pass from ridge eastwards, the older rocks dip or slope below the newer ones, so that we cross, after leaving the Mountain Limestone, first the Millstone Grit, then the Coal Measures, then the Permian Limestone, next the Trias, and so on over the Lias, the Oolites, and the Chalk.
Going Southwards from Doncaster, we get a similar experience. The outcrop, or appearance, of the rocks at the surface runs in a south-westerly direction from Yorkshire, and consequently when traveling from Leeds to London by the Great Northern railway the whole series is crossed from the Coal Measures to the Chalk, beyond which the Eocene of the London Basin is entered.
On stripping the newer rocks from the model, we find as we approach the underlying Coal Measures that an east to west ridge runs through Market Weighton, about ten miles north of the Humber, and abuts on the Pennine ridge north of Leeds and Bradford. On the South, a north-west to south-east ridge, known as the Charnian axis, tuns from the south of the Pennines through Charnwood Forest.
In the neighbourhood of Louth, not far from Lincolnshire Coast, there are indications of a less marked ridge running north and south. These various ridges surround a basin, of which the Pennines are the western rim, the Market Weighton ridge the northern rim, the Charnian axis the south=eastern rim, and the Louth ridge the eastern rim. The Yorkshire and Derbyshire Coalfield lie in the western part of this area, and the interest in our local geological work during the last few years has been intensified by its bearing on the character of the Coal Measures below the more recent rocks to the east.
In the masterly report on the concealed portion of the Coalfield of Yorkshire, Derbyshire and Nottinghamshire, which Professor Kindall, of the University of Leeds, prepared for the Coal Commission, the conclusion suggested was that the Coalfield extended eastward to the neighbourhood of Louth, and south-eastwards into Cambridgeshire. Professor Kendall think the axis of the coalfield basin lies near Doncaster somewhere between Haxey and Arksey, and that the coal seams, which are getting deeper and deeper as they approach Doncaster from the west, are rising to the surface on the eastern side of the district.
He points out that the boring at Haxey proved the Barnsley bed, which is the principal seam I the southern part of the Yorkshire Coalfield, at a depth of 1,454 feet below the base of the Permian, and that the measures were reported as “perfectly flat.” At Arksey, the Barnsley bed was reached at a depth of 1,320 feet higher than at Haxey. At Cadeby, which is on the down throw side of the southerly Don fault, the depth to the Barnsley seam is 2,250 feet, and it is in the Cadeby Cliff, as exposed by a cutting for the Dearne Valley Railway on the north side of the Don, that our most important contribution to the subject was discovered.
For it is there that we found a characteristic fossil of the Upper Coal Measures in the form of a fresh-water snail known as Anthracomya Phillipsi. This occurs plentifully in a thin red layer of ironstone some 30 feet above the top of the Cadeby shaft, and about six feet below the base of the Permian. The depth, therefore, at Cadeby from the Permian base to the Barnsley bed is 2,286 feet, or 966 feet more that at Arksey. The difference is mainly due to the position of the Cadeby shaft on the downthrow side of the great fault, and to the denudation of the top beds of the Coal Measures on the other side of the fault before the Permian rocks were deposited.
If the beds so worn away included the Anthracomya layer, the Middle Coal Measures, which are the most productive of the series, will probably be pierced at workable depths below the newer rocks. If, on the other hand, the Anthracomya series still lie above the Middle Measures, the more productive coal seams mat be at too great a depth to be readily worked.
We are now waiting to see whether this interesting red band will be found in the Bunter sinking. At Brodsworth, where the shaft is well into the Coal Measures, there has been no sign of the red band, but some dark shales at a depth of about 350 feet below the Permian base have yielded specimens of the characteristics shell.
In the chart prepared by Dr. Wheelton Hind and Mr. J. T. Stobbs of the fossil shells found in connection with seams of coal and ironstone in North Staffordshire, this particular fossil is shown above the Bassey mine ironstone is a black band, which Mr. Stobbs tells me has its laminoe crowded with Phillipsi. The matrix of the specimens sent him from Cadeby has a look about it, he says, of the Etruria Marl series. It is interesting to note that the base of the Etruria Marls is some 300 to 450 feet above the Bassey Mine coal, and that the Bassey seam is near the top of the grey or chief coal bearing measures in Staffordshire.
Soon after this fossil band had been seen at Cadeby, Mr. A. Jordan was fortunate enough to find similar shells on the south side of the Don in some grey shales at the bottom of the clay pit at Conisbro’ Brick and Tile Works. In Green’s memoir on the Yorkshire Coalfield, the beds exposed in this pit were referred with some hesitation to the Upper Coal Measures, and it has since been claimed by other experts that the fossils from a plant bed about 25 feet below the base of the Permian, are proofs, not of Upper but of Middle Coal Measures. The occurrence of the Anthracomya Phillipsi at a lower depth now places the point beyond dispute.
The description of this shell, in Dr. Wheelton Hinds’ monograph on the “Carbonicola, Anthracomya, and Naiadites,” is as follows : –
“Specific Characters:
Shell transversely obliquely oval, modioli form, elongated in a diagonal direction. The anterior end is small, its margin rounded. The posterior end is compressed, expanded downwards and backwards, while above it is rapidly compressed into the upper border, which is elevated posteriorly. The hinge line is straight, about one-half the length of the diagonal of the shell. The ventral margin is convex, passing with a gentle curve into the anterior end, and becoming straight shortly before it reaches the posterior end. The umbones are anterior and directed forwards, very blunt and gibbose, the beaks themselves inconspicuous. The shell itself is fairly tumid, and the valves are gibbose. There is no sign of an oblique constriction anterior to the gibbosity, which is itself very gradual in its form. Behind the gibbosity the valves are so rapidly compressed as to become hollow on the posterior slope.
Interior : As far as can be seen,” from the type specimen, “ which is a cast, the interior is normal, but the anterior adductor scars are not seen owing to damage to the specimen.
Exterior : The surface is covered by fine and course striae and lines of growth, which have the general arrangement which obtains in this genus. Periostracum thick and wrinkled.
Dimensions : The type specimen measures greatest diagonal, 20 m.m.; greatest dorso-ventral, 12 m.m.”
The way in which this fossil seems to have thrust itself under our notice since we first met with it at Cadeby is remarkable. Remember, please, that it had not been previously known as occurring in Yorkshire. Yet soon after it had been discovered in the railway cutting, next at the Brick and Tile Works, and then in the core of a boring near the Red House, Mr. Grace found it in some grey boulders which were turned out at Bentley: and it has since been seen in some grey rocks from the Balby boulder clay. These two latter finds show that it is somehow in situ in grey matrix in the course taken by our glacial debris. Within the last month it has been found, as previously stated, in the Brodsworth sinking in a dark shale about 350 feet below the base of the Permian.
The Coal Measures in the Cadeby cutting have an apparent dip or slope of 7 degrees to the south-east. The dip of the Permian beds above them is a trifle less. The fossiliferous layers characteristic of the of the lowest beds of the Permian limestone in this district are found at Cadeby about 8 ½ feet above the base, which consists in that section of 4 ¾ feet red and grey sandstone, ¾ feet grey sandstone, and 3 feet yellow sandy limestone. Some 40 feet higher, with pink and grey limestone intervening, are fossiliferous beds similar to those in Edlington Wood.
It is instructive to compare this section with Green’s record of the Permian base in the Conisbro’ claypit. What he saw was 2 feet very pale grey marl and shale, with a sandy micaceous bed, then 2 inches of yellow sandy limestone, above which was 1 foot 7 inches of marls, and then another inch of limestone. As recently measured, at a point further back than seen by Green, the clay pit shows 4 feet pink and grey sand with irregular beds containing small pebbles and bits of clay, above which is 18 inches of red, grey and blue clay, followed by 18 inches of yellow sandy limestone. Then there is 16 feet of grey shales surmounted by 11 feet of limestone, the top of which is fossiliferous.
In the Brodsworth sinking, the Permian base was a highly fossiliferous grey limestone. At Watchly Crag, between Hickleton and Hooton Pagnell, the Permian base is a quicksand exceeding 17 feet in thickness. These particulars, which have been obtained within an area of eight square miles, show considerable variations in the Permian base, and suggest that at the time of its formation the floor was shallow and undulating, and probably faulted, and that some of the early muds and sands were washed away before the limestone was deposited. At Brodsworth there is no sand or shale, at Watchly Crag and at Cadeby there is sand and no shale, whereas at Conisbro’ there are the sands, then shale and limestone, and above the first limestone some 16 feet of evenly bedded shales.
On the south side of the don, which is crossed by an impressive viaduct, the Dearne Valley line cuts deeply into the limestone below the Conisbro’ road, and within the next half mile it shows two noteworthy features. One of these is some thin-bedded limestone in troughs at the top of the massive rock. The lower limestone in the Doncaster district is typically massive, whereas the upper limestone, separated from the lower by the middle marls, is usually thin-bedded. In this section, however, some of the lower limestones show the thin-bedding characteristics of the upper limestone. These thin beds in wedge-like patches within troughs in the surface of the massive rock, and they pass into the thin beds forming ridges on either side. The whole section is bent in gentle curves in various directions, and the thin bedding in the troughs is probably due to bending, just as a many ply cardboard when bent to and fro may split into thin layers at the acute part of the bend.
The other special feature is a large mass of pulverulent or friable limestone. Small quantities of such material are a common feature in the Magnesian Limestone in this district, the numerous cracks and joints being often filled with it. Large masses of such material are frequently found in the north, but it has not previously been seen to anything like the same extent in this neighbourhood. The cutting shows large irregular dykes and sills of it. Two of these dykes are 10 and 15 feet thick, respectively, and they communicate with a sill 150 feet long, and from 6 feet to 8 feet thick. The dykes start from the surface and are evidently due to percolating moisture acting on the stone, and working horizontally on reaching a level at which the composition or condition of the rock favoured the process.
A little further east the cutting crosses a fault which has thrown the upper limestone almost against the lower, leaving between them only a thin band of middle marls with traces of gypsum.
Green and red marl bands occur in wide sweeping arches and troughs in this section, which is transversed twice by shallow valleys, and twice by a deep winding valley partially filled with silt.
The next cutting eastwards is on the Loversal road near St. Catherine’s, where there are 22 ½ feet of the middle marls with gypsum bands, and about 60 feet of Upper Limestone. In the highest part of this limestone is a fossiliferous band, which has been traced from Tickhill through Hexthorpe Flatts and Newton to Scawthorpe and the Woodlands, and thence to Burgwallis. The discovery of the fossiliferous band in this cutting was the more satisfactory as it had been looked for in vain in the adjacent quarry west of Loversall road, its absence from which is due to denudation acting on the valley slope.
Between Conisbro’ road cutting and the St. Catherine’s cutting, at a point about a quarter of a mile north-east by north of Alverley Grange, an excavation for a culvert disclosed Triassic sand. It had previously been suggested that the sand in the north of th plantation below Edlington Crag was Trias, but the evidence was uncertain. The Alverley excavation confirms the suggestion, and shows that the conjunction, horizontally, of Trias and Permian at Balby and Hexthorpe extends westwards.
On the further, or eastern, side of the St. Catherine’s cutting, where the upper Limestone dips into the low-lying lands of Potteric Carr, there is again some interesting evidence regarding the Triassic sand. This consists of a band not more than a few inches thick, but it is sufficient to show that the Triassic beds once lay at a high level on the limestone in Potteric Carr, and that they were subsequently swept away, leaving only this narrow fringe, like the film of cream round an emptied milk bowl, as a reminder of their former presence.
Crossing from the Dearne Valley Railway to the South Yorkshire Joint Railway near Wadworth, we again touch the eastern edge of the Upper Limestone, and then find in the cuttings between Wadworth and Tickhill that the limestone is covered in some places by the Upper Permian marls, and in others by bands of grey and red clayey sands, above which lie sands of many colours well deserving the name of the Bunter or variegates series. These sands, too, occur in areas which had previously been mapped as Upper Limestone. Such is notable the case at Gallow Hill on the south side of the Tickhill Road, where 16 feet of red sands rest on grey and red clayey sands which are exposed to a depth of 10 feet. This hill forms an outlier, that is a deposit cut off by more ancient rocks from the formation to which it belongs, such isolation being due to the denudation or wearing away of the once intervening beds of sand. The limestone floor round this and other sand hills shows the shell beds in many places; and in one of the cuttings there is a fine example of little hollows and ridges having been worn in the surface of the limestone before the clayey sands were washed on to it.
The excavations for the bridge by which the Rossington bridle way crosses the railway exposed a pronounced bend in the limestone subsequent to the deposition of the marls which for a few feet upwards are bent in precisely the same way. These marls are there covered by contorted marls and sands, through which a small stream subsequently hollowed its way, afterwards filling the hollow with silt and gravel. In the limestone floor of the adjacent cuttings an arch or anticline has been uncovered with its axis from north to south. The western side of this arch is abrupt, with a dip of 30 degrees. The eastern side has a long slope with a dip of 15 degrees.
On the limestone, and on the superincumbent marls and sands, lie the Wadworth and Tickhill glacial deposits, the description of which forms the third and final division of my subject.
But before dealing with them, I must remind you where we were in regard to out knowledge of the glacial and more recent deposits in this district before the new railways and collier sinkings were commenced. The Balby boulder clay – one of the best examples of boulder till in Yorkshire – was considered the most southerly deposit of glacial debris in the country. The discussions as to the route by which it reached Balby were wont. Like most debates on glacial problems, to become somewhat warm.
Boulders from the Lake district had been found between Cusworth and Sprotbro’ and within a short distance south-east of Balby. Carboniferous grits and gannisters were known to exist in great numbers in the fields between Armthorpe and Cantley. Dr. Corbett had mapped these gravels and had shown that the carboniferous type such as known at Heck, and the Triassic type such as known at Retford, met each other on the watershed of the Don and the Trent. But in describing them had refrained from any suggestion as to the causes which had brought them there, and he had not expressed any view as to their age.
The clay at the Sandall Brickyard had been mapped as “laminated clay, ancient warp” and its borders had been drawn with an accuracy very creditable to the skill of the geological surveyor, but there was some doubt as to its relations to the gravels and the glacial deposits. If we went outside our own district, we had to travel to Escrick and to York to find the nearest moraines to the north. Southwards there was a patch of clay with boulders at Kneesall on the border of the Dukeries, but otherwise one had to go beyond Grantham for any traces of glacial remains. There one found the chalky boulder clay which tops the 400 foot contour near the Great Northern Railway Company’s Stoke tunnel. The cutting at both ends of the tunnel gives sections in this clay, one of the boulders being a mass of rock 430 feet long, and some 30 feet thick.
So impressed was Mr. Harmer, the Eastern Counties glacialist, by the mass and the wide extent of the Grantham clay, and by its position on the hills south of the Trent valley, That he insisted the Yorkshire glacial men must find proofs of the Vale of York ice sheet having reached Grantham, where it was wanted to push the eastern ice sheet on to the Grantham hills. Failing traces of glacial remains in the Trent valley his demand for this extension was so urgent that he pleaded the work was done by clean ice, that is, ice free from the fragments of rock such as proved in the case of the York, the Escrick, and the Balby moraines, that far-travelled ice really reached those places.
I sympathise with Mr. Harmer, because the position of the Grantham debris, its great thickness, and its wide extent in south-west Lincolnshire and beyond the border of the county, offer a puzzling problem; and if the power Mr. Harmer wants from Yorkshire is really necessary, it may be said in his favour that dirt-free glaciers are not a novelty, that the bulk of moraine stuff is usually local, and that sands and gravels of the Trent valley between Doncaster and Grantham would not lend themselves to permanent records of ice-movement.
We started then, when the railway and the pit sinkings began, with two momentous questions, or, at least, we thought they were momentous. We wanted to know what were the relations of the glacial deposits to the Sandall clay and the watershed gravels, and from where, and in what direction the glacial materials had travelled.
The Bentley pit sinking gave great help. If its revelations when the coal measures are reached are as interesting as those it has provided in regard to the superficial deposits of the district, there is a good time before us in the near future. And here let me say how much we are indebted to the courteous managers at the colliery, Mr. Clive, and Mr. Prior, for the opportunities afforded for the examination of the tips. Mr. Bunting and Mr. Shaw for the Brodsworth Colliery, Mr. Clayton and Mr. Lovatt for the Dearne Vallet Railway, Mr. Whittaker for the South Yorkshire Joint Railway, have equally kind in the facilities given for watching the works in progress under their control.
At Bentley the superficial deposits, that is, the deposits above the Triassic sand, were 100 feet thick. Only 25 feet of this 100 feet is above sea level. The first point, therefore, to notice is that the old valley floor is here 75 feet below sea level. At Barnby Dunn the old floor is 170 feet below sea level. Sinkings further north give similar results. At Selby, the superficial deposits are about 70 feet thick and at Cawood, north-north-west of that place, they measure 94 feet. In fact, wherever a boring is made in the Vale of York there is proof that the ancient floor of the valley is below sea level. This indicates that the land was once higher than now, otherwise water could not have run down the valley and excavated it. It also reminds us that if the valley had not been subsequently dilled with glacial debris and river warp, its smiling pastures and rich arable acres would now be watery wastes. The City of York itself is built on a moraine, and owes its commanding position to the elevation this moraine gives it above the surrounding country.
The first 80 feet of the Bentley sinking shown several feet of laminated clay of similar character to the Sandall clay. Below this clay there as silty clay and warp plentifully sprinkled with bits of coal such as would be washed down by the don and Hampole beck from the coal seams outcropping on their banks. Then at a depth of 80 to 100 feet the surface there was a mass of glacial rubbish containing ice-scratched boulders up to a cubic foot and more in size. These boulders were mostly Magnesian Limestone. There were also carboniferous grits and ganisters, and a few carboniferous or mountain limestones. I have already mentioned the coal measures shale with Anthracomya Phillipsi. The presence of the latter shows that the boulder clay did not travel via York, for there is no Anthracomya Phillipsi to be obtained in that direction. We can only look for it in the west in the don or Hampole valleys, from which direction the other boulders in the Bentley assemblage can very well have come. It may be urged, on the strength of a few fragments from the Balby clay, that there was a mingling of the ice-sheets at Doncaster, and that the western ice and the northern ice, and possibly the eastern ice, shot their burdens in the corner of the Vale of York. What more likely, in deed, in view, first, of the huge mass of ice which filled the Vale of York in the north, then of the evidence of the ice having filled the valley of the Dearne in the west, and next of the eastern ice pushing its way through the Humber gap. But, be that as it may, our recent discoveries support the north-western route.
Bentley, then, settled one matter for us, and threw light on the other. It showed the Sandall clay was post-glacial, and it suggested the western origin of the boulder clay. It also suggested that sinkings further north in the Vale of York may reveal boulder clay below the superficial clays and gravels. Borings are not likely to do this as the cores are small, and the boring tool pushes the stones on one side in such material as boulder clay instead of bringing them to the surface.
Th railway cutting through Shaw Wood , about half a mile south-east of Sandall Brick Yard, showed 19 feet of bluish-grey clay similar to that near the top of the Bentley sinking. It was a finely laminate clay, the laminae or leaves being as thin as tissue paper. Each layer represents a flood of muddy water from which the clay settled to the bottom, covering the previous flood and in its turn being covered by the clay from subsequent floods. This clay resting on its southern margin on a shelving bank of Triassic sand. Above the clay was 6 feet of sand and gravel, consisting of gannisters, grits, cherts, and quartzites.
On the south side of Armthorpe road the ridge of gravel and sand which stretched from the Balby tram terminus to Hatfield, is pierced by the cutting. There are numerous excavations elsewhere in this ridge and in all of them the gravels are strongly current bedded, having evidently been washed now this way now that way by converging streams of considerable velocity. The Armthorpe cutting, however, revealed an additional feature. If first showed 16 feet of the gravels in wedge-like masses dipping in all directions. Below these were 14 feet of sands and gravel, also current bedded, bur with gentler slopes suggestive of less powerful streams, and under these was 4 feet of grey sand and clay with quartzite pebbles and grit and gannister boulders up to a cubic foot in size lying on the Triassic floor. Such boulder material has not been seen elsewhere in the gravel pits in the ridge, but this is possibly due to the excavations not being sufficiently deep. If not actually deposited in its present position by a glacier, it can have been washed only a short distance from the termination of one. Its appearance reminded me more than other glacial remains in this district have done of the debris one sees in the “Gletsch” below the tongue of the Rhone glacils.
From the glacial debris, and the overlying clays and gravels at Bentley and Armthorpe we pass to Wadworth and Tickhill deposits, noting on the way that the deep cutting in the Triassic sand at Rose Hill, south of the Race Course, is covered by some 8 feet og gravels and sand similar to the gravels and sand I Shaw Wood, and that the Triassic floor in the Carr lands, south of Doncaster and Balby, is only three or four foot below the surface. This surface, as a rule, consists of amount nine inches of peaty soil, below which is a foot of wet blown sand, and then a foot or so of clay. Near the water courses the clay is frequently five or six feet thick. Professor Kendall, who has devoted much attention to the ancient floor of the Vale of York, and its remarkable contract with the higher level of the sea floor of Holderness prior to the glacial period, asked that special attention might be paid to the depth of the superficial deposits on the Carr, and the observations made show that the old hollow of the Vale of York did not extend more than a very short distance south of the Don.
Near Wadsworth, at the spot where the Rossington bridle road meets the slope of the Upper Magnesian limestone, we enter the series of cuttings which have revealed the most southern accumulations of glacial debris yet seen in Yorkshire. There are four cuttings through glacial matter, the most southern being at All Hallows hill, three-quarters of a mile north-west of Tickhill Church. The first excavation is roughly triangular, being, so far as the exposure of boulder clay is concerned, some 20 to 120 yards wide, and about 200 yards long. It shows a mass of sandy clay, red in some parts and grey in others, sprinkled throughout with large and small boulders.
The deposit rests in places directly on the limestone, and in others on Upper Permian marls and red and grey Triassic sands. In the deepest part of the cutting it is 24 feet thick, and from it have been obtained magnesian limestone boulders of all sizes up to 12 cubic feet. Many of these boulders are deeply scored with ice scratches. There are also blocks of coal measure sandstones, some gannisters, and a fair number of carboniferous limestones, measuring up to a foot and a half cubed.
The next cutting through boulder clay is near the Wellingley road, but it shows only two feet thick of clay with limestone fragments and a few grits lying on variegated sands with marl bands.
Then near the Tickhill road there is a cutting through some 20 feet of boulder debris, from which, in addition to the usual heap of Permian stones, some fossiliferous limestones were obtained. These contained Productus Cora, P. longispinus, P. scabriculo-costatus, and Aviculopecten. Encrinital blocks were also seen.
At All Hallows hill, which is marked on the map as Magnesian Limestone, a cutting went through 180 yards of tough red boulder clay, 19 feet thick in its deepest part. The clay rested on and against grey and red marls and sands, The clay was so tough as to require blasting for its dislodgement. It contained Magnesian Limestone boulders as large as those near Wadsworth, grits up to half a foot cubed, and well-polished and scratched mountain limestone up to a foot and a half cubed. A piece of shaley limestone yielding specimens of Derbyia, Camarophoria, Spirifer bisulcatus, and Productus punctatus probably came , Dr. Wheelton Hind tells me, from the Harrogate district. In one place was a patch of grey sand about 2 feet in diameter, which had been rolled up in the clay. The bulk of the boulders were from the lower Magnesian limestone, and probably came from the western escarpment of that rock, or from either sides of the valleys, such as the Don and Hampole valley, which cut the Magnesian Limestone transversely. The coal measure sandstones and the mountain limestones again suggest a western or northwestern origin. The debris may have come down Airedale or Wharfedale, but how is it that it rests on the slopes of the hills on the western edge of the low-lying Triassic country?
If it came down the Vale of York it must have been pushed against this western edge by ice acting from the east. There are now no traces of such eastern ice, unless the boulders at Gringley-on-the-Hill, of which there are a fair number, are the relics of an ice sheet which stretched across the ten miles of country inventing between that place and All Hallows. I am inclined to view that the All Hallows ice came over the limestone country west of Wadworth; that the Triassic lands were then the floor of a wide lake which was held up on the east by the North Sea ice and was fed from the south by the waters of the Trent, and from the north by the melting edge of the Vale of York glacier; and that the western ice shot its debris on the sloping shore of this lake in fairly deep and quiet waters. For if the ice had rested on a slope, down which the water from its melting edge could have flowed rapidly, the fine material in which the boulders were encased would have been washed away. This, I think, also applies to the tough till of the Balby deposits.
Nothing similar to the characteristics of the Balby and Tickhill boulder clay is seen in the material at the foot of a Swiss glacier. The fine mud which might form accumulations of clay is being carried away in streams of turbid water, and when the glaciers retreat the moraine rubbish left behind consists of boulders and heavy particles of sand, The fine mud, such as forms the greater part of the Balby and Tickhill moraines is in Switzerland carried down the Rhine, the Rone, and the Reuss to settle free from glaciated boulders in the depths of the Bodensee and the lakes of the Geneva and Lucern.
If we Proceed to summarise the different formations recently exposed in our local rocks, we are reminded in the first place of the lagoons and estuaries in which the sands and clays of the coal measures were deposited, As the mud and sand banks rose above the waters they were covered by luxuriant and wide-spreading growths of vegetation, These sank again and again below further accumulations of sand and mud, and the thicker growths of vegetation ultimately formed coal seams. Sometimes the vegetation was carried into its present position by floods. Such are the canal coals of irregular structure with fish remains entangled in them. Now and again the sea broke in, and left its traces in bands of salt water molluscs. But the predominating character of the shell beds in the measures is their fresh-water aspect.
After the close of the coal measures period the rocks were uplifted, being much faulted in the process, as also beforehand and subsequently. An episode of denudation followed, and they then sank below the waters of the Permian period which formed an inland sea under arid and climate suggestive of Caspian conditions. Owing to rapid evaporation the concentrated waters deposited the magnesian and calcium carbonates of our local limestone. This phase gave place to the desert conditions under which the Triassic sands and marls accumulated. The position , however, of the Balby and the Alverley sands show that there was a local upheaval and denudation of the limestone before the Triassic sands were laid upon it. There is no evidence locally of the Lias, the Oolites and the Chalk having rested on the Trias. For that we must go eastwards or southwards beyond the Trent. But the glacial debris reminds us of the immense sheets of ice which in a comparatively recent period spread themselves from the Lake district and from the Pennine Range, the Shap Granite and volcanic rocks of the former, and the carboniferous limestone boulders of the latter. In our gravels, we see evidences of the great floods which poured into the Ouse and Trent valleys in glacial and post-glacial times; and on measuring the silts and warps north of the Don we realise that the depression of the Vale of York once formed an area of the sea bounded on the west by the Permian rocks, and on the east by the Yorkshire Wolds; and that its present habiteness is due to the moraines of the ice age, and to the sediments washed from them or accumulated when they blocked the discharge of the waters eastward.
Finally, what are the present problems for local investigations?
The most urgent are in the Coal Measures. We want more precise information as to the character of the beds forming them. We want to know what faults have disturbed them, and how far the direction of these faults and the influence of corresponding monements and subsequent denudation, can be inferred from the positions of the overlying rocks. We want to know what fossils the coal measures contained, and at what depths they have been found.
A fossil chart similar to that prepared by Dr. Wheelton Hind and Mr. J. T. Stobbs for North Staffordshire is also wanted for Yorkshire. In addition, the marine bands characteristic of other coal-fields need searching for.
A more extended examination and Correlation of the various aspects of the Permian base is wanted. The fossil lists for the local Magnesian Limestone are not so full or so precise as is desirable. Fortunately there is some hope of Mr. W. S. Bisat taking this in hand.
Our upper Limestone is absent from the main Permian series of Nottinghamshire. It should be followed southwards for the purpose of seeing whether it can be connected with, and is there represented by, some other rocks, such as the Marls occupying a similar position.
The chemical composition of the Lower and the Upper Magnesian Limestones, particularly of the numerous varieties making up the former, offer an attractive task for the chemical section of our Society. The physical section and the microscopists will find an inviting field in the comparison of the Permian marls and sands.
The mapping and classification of the gravels in the northern Trent valley, and their relations to the Triassic sands also deserve attention. The examination of the sands would throw light on the desert conditions under which they were accumulated, and it is possible the enterprising student might find some footprints in them similar to those discovered in Triassic districts elsewhere.
The tracking of glacial boulders southwards is an urgent piece of work, which can very well be combined with the other subjects of research.
Northwards, the Askern and the Kirk Smeaton gravels, which chiefly consist of Magnesian Limestone, offer an inviting problem, the answer to which will elucidate the history of many of the valleys in the Permian rocks, and will show how far they are due to the varying positions of the ice in the glacial period.
I have sometimes heard it suggested that the geology of Doncaster is uninteresting. One rash person, indeed, warned me at the commencement of my local geological rambles that the district could be exhausted in a couple of days. Now the fact is, there is an infinite variety of attractive geological detail in this district, which custom cannot stale; but the leading features have a simplicity in the leading features is an advantage to the field student, who thereby sees the effects of simple causes on a wide scale, and is then led to the study of the more complicated phenomena of which, as I have attempted to show to-night, the district offers a rich harvest for cultivation.
Dr. Corbett, Mr. Jordan, Mr. Stiles, and the President (Mr. T. Watson), took part in an interesting discussion.
[A cutting from the Doncaster Chronicle]