# Midland Naturalist/Volume 01/Some New Features in the Geology of East Nottingham (continued)

Some New Features in the Geology of East Nottingham.
By J. Shipman, Esq.
(Continued from page 20.)
Not the least important respect wherein my map differs from the Government map is the much less area covered by Upper Keuper marl. The Geological Survey supposed that one effect of their two faults was to throw in between Lower Keuper a patch of Upper Keuper extending from Cranmer Street to Red Lane—that is, the space between the two faults. If their supposed curved fault had really existed I believe this would have been correct; but, as it is, the Upper Keuper, of which the Reservoir Hill consists, is cut off on the north side by No. 2 fault, and does not come in again till the ground rises to form Mapperley Hills. Then they mapped the Hunger Hills as being to a great extent composed of Upper Keuper. This is not so, however. The flat-topped appearance of these hills is caused, apparently, by a bed of sandstone, three or four feet thick, seen also in the cliff of Lower Keuper on Coppice New Road; and the Upper Keuper may be traced by the sudden rise of the ground, ​it a more rounded contour, and by its finely laminated character and bright red colour, as contrasted with the purplish and dull red of the highest beds of the Lower Keuper.
We come now to the most interesting feature of all that may he said to be new in the geology of this part of Nottingham. Running along the boundary line separating the Lower Keuper from the Bunter (f2) on the new map you will observe a narrow band coloured blue. That is the conglomerate forming the lowest bed of the Keuper in this district. It was seen at short intervals along the boundary all round the double tongue of Banter in the St. Ann's Valley; and, although tolerably persistent, it is sometimes represented by a mere string of pebbles. The tracing of this conglomerate along the base of the Hunger Hills and round the opposite side of the valley to where it was cut off by No. 2 fault in Dame Agnes Street fairly did away with the theory of the curved fault; for, according to the Survey map, this valley ought to have been in Lower Keuper. The best exposures of this conglomerate were in Turner Street and on Hunger Hill Road, the section in Turner Street having the advantage of showing a perpendicular section, while on the Hanger Hill Road it had to be studied during the process of excavating. In Turner Street its greatest thickness was 22in., and it there consisted of rounded and partially rounded pebbles of all sizes up to boulders five or six inches long, consisting for the most part of quartz and quartzite, with a few bits of brown magnesian limestone, volcanic ash, basalt, greenstone, chert, slaty rock, and Coal Measure rock, the whole being firmly compacted together by lime and magnesia and oxide of iron, the latter giving it a strongly ferruginous aspect. Such is its compactness, indeed, that navvies who happen to have to excavate it have learnt to dread it, and affirm it to be the toughest rock they ever met with. It rested in the shallow cavities of an eroded surface of the Bunter, sloping to the east at an angle of about 5°, and was surmounted by first about 18in. of coarse mottled sandstone, then beds of finely-laminated brown and light olive-green sandstone, with thin partings of red marl. At its outcrop on the top of the low rounded hill of Bunter on Hunger Hill Road, the conglomerate, which, with its associated beds, formed a band at the surface about 50ft. broad, had much the same composition as in Turner Street, only there was more chert and a good deal of white limestone in lumps and ground-up, there being also calcite in minute crystals, and as a thick coating to some of the pebbles; it was about eight inches thick, and covered by first a thin bed of greenish grit, cemented into cakes by calcareous matter, then by an irregular series of bods about three feet thick, consisting chiefly of unconsolidated white (bleached) sand, false-bedded, and streaked with pate green and yellow, with occasional strings of pebbles enclosing lenticular beds of sand, of a ferruginous colour. The whole, though very irregularly bedded, had a general inclination to the north-east, passing under the Keuper. When a perpendicular section of these beds was exposed further wider the Keuper, they presented a peculiar variegated wavy appearance, being streaked with red, yellow, and pale green. I was struck by the remarkable resemblance between these beds and the raised beaches I had seen on the sea shore, the only difference that I could perceive being the complete absence of any traces of life. Among the pebbles forming the conglomerate at this spot, I found what appears to have once formed the extremity of a sea-worn pinnacle of greenish fine-grained (Silurian?) sandstone, such as may be seen at the present day along coasts where Silurian or Cambrian rocks are exposed. That this was its origin seems to me to be indicated by its peculiar water-born aspect, and by the lateral grooves along the lines of stratification.
A very instructive section has lately been exposed in Ford Street, ​nearly along the dip of the Keuper, The conglomerate was here seen just before it crops out, occupying cavities in a gently sloping plane of the Bunter. The pebbles of the conglomerate blended with the overlying sandstone and marl, and the variegated beds swelled out slightly in the direction of the outcrop. The accompanying woodcut is from a sketch taken on the spot.
Junction of Keuper and Upper Bunter, Ford Street, Nottingham.
* e. Thick-bedded soft brown, yellow, and light green sandstone, with red and green finely-laminated marls (Lower Keuper.)
* d. Ferruginous band (6in.)
* c. Soft sandstone, streaked with green, red, and yellow.
* b. Conglomerate, forming base of Lower Keuper (f5), filling eroded cavities in the Bunter (f2), 20in.
* a. Bunter sandstone, yellow, "false-bedded," with a few pebbles,
In this section the Keuper appears to dip to the south, the true dip, however, being south-east,
The conglomerate was twice passed through in Dame Agnes Street during the excavations for the culvert, caused by a fault, as shown in section No. 1, wend was there found to be divided into two strings of pebbles by a lenticular mass of coarse greenish-while sandstone about 4ft. thick. I met with a similar development of sandstone at the base of the Lower Keuper at the bottom of the new road through Patchitt's Park from the Reservoir to Red Lane, about 5ft. of unconsolidated yellow sandstone, streaked with red, and passing up into soft red marl, coming immediately above the conglomerate. The most easterly spot where I have seen the conglomerate is near the Westminster Abbey Tun, where the pebbles were embedded in a coarse red sand overlaid by greenish-gray marl. It has been met with as far east, however, as the first brickyard on Carlton Road, where it was penetrated after passing through 105ft. of Lower Keuper. The only localities where this conglomerate may now be seen to any advantage are in Calcutta Street, where the brown sandstone cropping out of the sloping ground from above the Bunter is studded as thickly as it will hold with pebbles, forming a band 22ft. across, with a thickness of about 3ft.; and in Red Lane, where it is seen encrusting the old surface of the Banter. Although this section was carefully examined by Aveline, and described in his "Memoir on the ​Nottingham District," (Sheet 71, N.E.,) he either did not observe this conglomerate at all, or mistook it to belong to the Bunter, for he mentions a less important conglomerate, about 16ft. higher up in the Keuper, but says nothing about the conglomerate at the bottom. This second conglomerate is well exposed in the section in Turner Street, also in the open ground at Belle Vue Terrace, at the top of Calcutta Street. Its maximum thickness is 12in., and it consists of small white and pink sub-angular quartz pebbles, flakes of fine red marl, pebbles of pink and white limestone, fine-grained light green sandstone, and bits of rock embedded, in one spot in calcareous fine yellow sand, in another in Indeed, I found quartz pebbles calcareous greenish-white sandstone, distributed more or less throughout the lower beds of the Keuper sandstone along Blue Belle Hill.
With regard to the origin of the conglomerate forming the base of the Keuper, it is, of course, well not to attempt to draw conclusions in geology from too limited an area. There can be no doubt, however, that in this conglomerate, with its associated irregularly-stratified beds of sandstone, we have the remains of an ancient sea-beach the shore of the sea in which the Keuper sandstone and clay were deposited. The pebbles composing the conglomerate are all such as may be seen in the underlying Bunter the partially consolidated sandstone is easily recognised as Bunter sandstone that has been bleached, then re-deposited, and subsequently tinged with colouring matter. We know that the Bunter sandstone formed the land surface over a large part of England during what was probably a long interval, while the Muschelkalk of Germany was being deposited. Thus the conglomerate probably represents a great break in time in this part of England and the fact that the plane of Bunter on which the conglomerate rests is inlined at a greater angle than the dip of the Bunter, as far as that dip can be ascertained, leads me to infer that the old Bunter land was gradually submerged from an easterly direction, during which the pebbles which probably more or less covered the land-surface came to be re-deposited and cemented with carbonate of lime and magnesia, and partially interstratified with bleached sand derived from the receding shore line.
This work was published before January 1, 1930, and is in the public domain worldwide because the author died at least 100 years ago.
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