Charnwood Forest Research Articles

Letters to Editors

THOUGH the discussion of the age of the rocks of Charnwood Forest is not likely in the present state of our knowledge to lead to any useful result, there are still a few points in Prof. Hull's letter on the subject which seem to call for remark. In the first place the late Prof. Jukes was by no means so strongly in favour of the Cambrian age of these rocks as Prof. Hull states. Prof. Jukes' words, in Potter's (not Porter's) “History of Charnwood Forest” are as follows:—“It is therefore uncertain whether they (the rocks of Charnwood) belong to the Devonian, Silurian, or Cambrian systems, the probability only being in favour of the latter.” Secondly, the Cambrian of Sedgwick includes a great deal more than the Cambrian of the Geological Survey, and therefore there is not the perfect unanimity between these two authorities that Prof. Hull's remarks would lead us to believe. Thirdly, if lithological resemblance is to go for anything, it may be used directly against the Cambrian age of the rocks. On the western side of the forest we find sheets of crystalline rock and beds of highly altered conglomerates and breccias, which have a suggestive likeness to the lava flows and ash beds of the green slate and porphyry series of the Lake District. I don't say the resemblance proves anything, but it is worth quite as much as the similarity between the slates on the east side of the forest and the slates of Llanberis. Mr. Bonney has also called attention to the fact that the strike of the Charnwood Forest rocks is the same as that of the Volcanic Series in the Lake Country, when that group is last seen. Again, it is far from certain that the rocks of Charnwood Forest are all of the same age. I recollect seeing many years ago some sections (of which I am afraid I have kept no record) that seemed to show that some of the bosses of Dioritic rock near Markfield were older than the slates that surrounded them. If this be so, perhaps these crystalline hills may be the projecting points of a nucleus of similar rock that underlies the whole area, and which may be Laurentian in age. The rocks are not gneiss, but I know of no reason why the equivalents of the rocks of the Hebrides must be gneiss all the world over; they are, however, rich in hornblende, and so are the Hebridian rocks. With all these possibilities before us, I am afraid it will be hard to arrive at that enviable state of security which Prof. Hull seems to have been in when he penned his letter.

The Age of the Rocks of Charnwood Forest

IT is no doubt to be regretted that Mr. Woodward, misled by insufficient authority, should have introduced, in his excellent work on the geology of England and Wales, still further confusion into the maltreated old rocks of Charnwood Forest, but I doubt whether their age is quite so certain as Prof. Hull seems to think. I fully agree with him that there is not a particle of evidence for their Laurentian age, and that their syenites and hornblendic granites cannot be correlated with the hornblendic gneiss of the Malverns, but I must demur to his grouping them with the Cambrian rocks of the Longmynds or of Llanberis. The authority of Prof. Sedgwick is great, but it must be remembered that the term Cambrian with him included far more than in the nomenclature of the Geological Survey, and I am not aware that he ever committed himself to the Charnwood rocks being equivalent to his Lower Cambrians. Except a slight lithological resemblance of some Charnwood rocks to those of Harlech and Llanberis, and a still slighter to Longmynd rocks, there is really nothing in favour of this special correlation. One point, however, there is which may give some clue to their age, which does not seem to have been much noticed hitherto, probably because the facts have been strangely overlooked in the Geological Survey description of the district. It is that beds of coarse volcanic agglomerate and ash abound among the Charnwood series. Further, the resemblance of the rocks as a whole (when not unusually metamorphosed) is very close to the “green slate and porphyry series” (or Borrowdale rocks) of the Lake District. Compared with the Welsh rocks, they are far more like those of Cader-Idris than of Llanberis. With these there is scarce any lithological resemblance, but if I mixed my Charnwood collection with those from the other two localities, especially the former, I should have great difficulty in separating many specimens. It seems then to me far more likely that this great volcanic activity in the Charnwood district should have corresponded in time with that in the Lake District or with some part of that in Wales, than that it should have happened in the age of the Harlech, Llanberis, and Longmynd groups, where we have no evidence of any volcanic disturbance. The argument may be summed up thus, as it seems to me:—The Charnwood rocks are old, so are both the competing groups; they are unfossiliferous, so are both; they are cleaved, so are both; they contain evidence of great volcanic action, so do the Borrowdale series, and not the Welsh Lower Cambrians. One point for the former. The general correspondence of their strike with that of the Borrowdale series under Lagleborough may also perhaps count for something.

The British Coal-Fields

ONE distinguished geologist, at least, disbelieves in the speedy exhaustion of our coal-measures, so frequently predicted of late. At the annual meeting of the Dudley and Midland Geological and Scientific Society, Prof. Ramsay delivered an address on the existence of coal beneath the New Red and Permian strata, in the course of which he observed that for fifteen years he had been preparing to attack this subject, but it was not until he became a member of the Royal Coal Commission he had given it a really searching consideration. There could be no doubt that the various coal-fields of the Northern and Midland districts once formed one great coal-field, but had been separated by extensive denudation. Another great coal-field was formed by the now distinct fields of Devonshire, South Wales, Somersetshire, and the Forest of Dean. Between these two great divisions, the north and the south, there was no connection formed by the coal-measures, the poorer measures possibly having been deposited there, but not the rich deep ones in the carboniferous era. Referring more especially to the Midland district, he thought it highly probable that coal-measures would be found to exist between the present boundary of the South Staffordshire district and the Forest of Wyre; but it was questionable whether it would be of a workable depth. On the west side of the South Staffordshire boundary, in the direction of Bridgenorth, Shropshire, he also believed coal to exist beneath the Permian strata, at a depth of 1,500 feet, or possibly more in some places. At the north of the South Staffordshire boundary, a line drawn from Wyrley right across to the Shropshire district would, he believed, include some valuable coal-beds, a considerable part, but not all, of which would be at a workable depth. He entertained no doubt that the coal-measures were continuous between the South Staffordshire and Shropshire districts, which, although in some places disturbed by denudations, might, throughout the greater part of the area, be profitably worked. In the North Warwickshire coal-field were found, in the direction of the Staffordshire boundary, five beds of coal, which gradually amalgamated, until on nearing Coventry they formed only two measures. The shale and sandstone were split up in like manner. These features constituted most important evidence in support of the theory that the Warwickshire, Staffordshire, and Shropshire districts were united by continuous coal-measures, the peculiarities referred to in the coal, shale, and sandstone strata being identical in all three districts. In that theory Prof. Ramsay was a firm believer. From Warwickshire to the south end of the South Staffordshire boundary, there was, he believed, coal, but not profitable. Towards the northern end of the South Staffordshire boundary, however, a line drawn from Coventry would include rich and valuable coal-measures. Between Staffordshire and Leicestershire the measures were also, he believed, continuous. From Wales to the Forest of Wyre there was profitable ground; but from Wyre on to Charnwood Forest, and east of that, there were no coals of value. The speaker expressed opinions equally assuring as to the presence of coal under the area lying between the north of the South Staffordshire boundary and the mountain limestones of Derbyshire. In one part of that district—viz., north-west of Cannock Chase—Prof. Ramsay said he should not feel the slightest hesitation in recommending a search for coal; and his belief in the presence of coal at a workable depth in the neighbourhood of Uttoxeter was equally strong. Now, supposing that his calculations were only approximately correct, the result would be surprising. It would amount to this—the coal now reckoned as available in the South Staffordshire and Shropshire districts was, in round numbers, 3,201,000,000 tons. If his belief were. a true one, this supply would be further augmented by 10,000,000,000 tons. In Warwickshire the proved coal-measures are estimated to yield 458,000,000 tons, and the measures he believed to exist in addition would be 2,494,000,000, or five times more than the present estimate. The Leicestershire field was calculated to possess 836,000,000 tons, and this would be supplemented to the extent of 1,790,000,000. What was the case in regard to these districts was, he believed, equally applicable to many other parts of Great Britain. The South Wales, Forest of Dean, Bristol and Somerset districts were exceptions to this rule, the coal there lying in basins caused by denudations, the surrounding measures being destroyed. In the Midland districts these small basins are not found, the whole forming one great basin. Lancashire, Derby, and the Yorkshire coal-fields were, however, subdivided by the process of denudation. Still, he had no hesitation in believing that the estuary of the Dee and the Mersey have lying between them beds of coal, although probably at too great a depth to be of practical value.

II.—Notes upon the Occurrence of the Post-Pliocene Drift of Charnwood Forest

During the investigations I made on the “Post-Pliocene Gravels of the Severn, Avon, and Evenlode, and their extension over the Cotteswold Hills,” the result of which I embodied in a paper read before the members of the Cotteswold Club in the early part of 1869, and is now published in their “Proceedings,” many of the boulders found by me, on examination by R. Etheridge, Esq., of Jermyn Street, were determined to be syenite and granite from Charnwood.

Scientific Serials

THE November number of the Geological Magazine (No. 77) opens with an article by the editor, Mr. H. Woodward, on Fossil Crustacea from various formations. The species described and figured by the author are Scyllaridia bellii from the London clay of Sheppey, and Palœga carteri from the lower chalk. One of the most important papers in the number is on the coal-bearing rocks of Southern Chile by MM. Lebour and Mundle. The coal appears to be only a kind of lignite; it is found in beds of tertiary age. Mr. Lucy contributes a paper on the Post-pliocene Drift of Charnwood Forest; Mr. H. F. Hall, a note on the Glacial and Post-glacial deposits in the neighbourhood of Llandudno; Mr. L. C. Miall, a paper on the formation of swallow-holes in mountain limestone; and Mr. E. Wilson, a notice of some altered clay-beds and sections in Tideswell Dale, Derbyshire. The remainder of the number is occupied as usual by reviews, notices, and miscellaneous matter.

Baden Powell and Charnwood Forest

Baden Powell and Charnwood Forest

The Trias of Charnwood Forest

The Trias of Charnwood Forest

II.—On the Igneous Rocks of Charnwood Forest and its Neighbourhood

The geology of Charnwood Forest appears to have been first systematically investigated by Professors Sedgwick, Whewell, and Airy in 1833. A very brief notice of their labours by C. Allsop, Esq., is appended to the history of Charnwood Forest by J. R. Potter, 1842, as is also a valuable and detailed memoir on the geology of the district, by J. B. Jukes, Esq.

V. Notes on Charnwood forest

In the midst of a comparatively tame and highly cultivated plain of New Red Sandstone near the centre of England, there rises up a part of the under crust of the earth which presents so much the appearance of an island as to lead the imagination at once to those remote ages when its porphyritic Peaks and Syenitic Knolls were surrounded by the sea. The geological history of this celebrated spot has been skilfully unravelled by Professors Sedgwick and Jukes (Article in Potters's Charnwood Forest); the Rev. W. H. Coleman (Article in White'Directory); Mr. Edward Hull (Memoirs of Geol. Survey); and others.

Guide to the Geology of Scotland, with a Geological Map and Plates

The next chapter gives a geological account of the road from London to Brighton, and the structure of the Brighton Cliffs ; we then have a few notes concerning the Great Western Railway and the neighbourhood of Bath, and next, a series of excursions in Derbyshire, commencing with a notice of that portiofi of the Birmingham and Midland Counties Railway between London and the station at Amber Gate, by way of Leicester. This latter trip is illustrated by a number of engravings and is given in some detail, and the chapter concludes with a short notice of the vicinity of Charnwood Forest.

XVIII. Observations, in objection to some new arrangements, and simplifications of the strata of England, proposed by Mr. Bakewell.—A defence of the reality and circumstances stated, respecting three great Faults or dislocations of the strata in and near Derbyshire.—On Mr. Silverwood's intended section of all the Derbyshire strata.—On Mr. Hall's Survey and Models of the high Peak of Derbyshire.—The Slate

XVIII. <i>Observations, in objection to some new arrangements, and simplifications of the strata of England, proposed by Mr.</i> B<scp>akewell</scp>.—<i>A defence of the reality and circumstances stated, respecting three great Faults or dislocations of the strata in and near Derbyshire.—On Mr.</i> S<scp>ilverwood's</scp> <i>intended section of all the Derbyshire strata.—On Mr.</i> H<scp>all's</scp> <i>Survey and Models of the high Peak of Derbyshire.—The Slate