Stonesfield Slate.-Report of the Committee, consisting of Mr. H. B. WOODWARD (Chairman), Mr. E. A. WALFORD (Secretary), Professor A. H. GREEN, Dr. H. WOODWARD, and Mr. J. WINDOES, appointed to open further sections in the neighbourhood of Stonesfield in order to show the relationship of the Stonesfield Slate to the underlying and overlying strata. (Drawn up by Mr. EDWIN A. WALFORD, Secretary.)

THE basement beds of the Great Oolite in the Midlands and in the southwest counties of England have been hitherto supposed to be well defined. For in all the records of the many writers on this geologic subdivision, to the Stonesfield Slate has been assigned the line of separation from the Fuller's Earth or Inferior Oolite, or, where the Stonesfield Slate is absent, as in the extreme west, to the Minchinhampton beds has been given the same position. Undue prominence has been given to so inconstant a series of beds as the Slate, as much from the ease with which fossils for its study have been collected as from the varied character of the fauna and flora found in it. From the days when the finding of the mammalian remains in the Slate called the attention of geologists prominently to it, every text-book of geology has found a place for it at the bottom of the Great Oolite limestones. Though, however text-books and papers have defined the lower boundary of the Great Oolite so clearly, the officers of the Geological Survey in their work in the neighbourhood of Stonesfield found the lines so difficult to define that it became necessary, where the Slate had disappeared, to adopt an intermediate colouring, a kind of no-man's-land. Since then an argillaceous stratum, 'the Rift bed,' has been recognised as the lowest of the Great Oolite beds in the Banbury and Hook Norton area.

2

The endeavour of the work, for which the British Association made a money grant in 1893, has been to ascertain the thickness and composition of the beds underlying the Slate, for hitherto no account of these beds has been obtainable, Professor Ed. Hull's record of 70 feet being the only assumed thickness of the Great Oolite, and to this he adds 30 feet for the Inferior Oolite. Though their thicknesses seem to be over-estimated, no correction or account of a series of rocks so important has since then beeu written. Nearer Chipping Norton, however, Mr. J. Windoes, Mr. W. H. Hudleston, and your Secretary 3 have worked at some of the debatable beds above the Clypeus grit, one of the highest of the Cotswold divisions of the Inferior Oolite. To the bulk of these beds has been given the name of the Chipping Norton Limestone' by Mr. Hudleston, and though the beds have not been reached in the section, they may be seen in the lane sections and near the spring on the banks of the Evenlode, south of Stonesfield. Your Secretary in 1892-93 sank a shaft near Ditchley, Oxon, to find out the true position of the Slate beds there; but of this an account will be published elsewhere.

2

The progress of the work, so far, at Stocky Bank, Stonesfield, has

Report Brit. Assoc., 1860, p. 82 (Sectional Proceedings).

W. H. Hudleston. Proc. Geol. Assoc., vol. v. No. 7.

E. A. Walford, On the Relation of the so-called. Northampton Sand of N. Oxon to Clypeus Grit,' Q.J. G.S., vol. xxxix. p. 235.

consisted in scarping the bank for 33 feet, and in continuing the section by carrying a shaft of 20 feet in depth through the lower bank. The purpose of the work has been so far successfully carried out by showing the existence of 30 feet of rock with some thin clay courses below the Slate. These limestones and clays (see accompanying section on p. 306) are of Great Oolite type. To reach the Clypeus grit will need an extension of time.

Your Secretary has, by the discovery of numerous species of corals on the ploughed fields on the bank top, been able to define the coral bed (Rift bed) so prominent a feature in the near section at Ashford Bridge. Seventeen feet below the coral bed a course of Slate is met with, almost thinned out at that point, and only from 5 to 7 inches in thickness; the total thickness of it and the associated beds (10, 12, 13 of the section) being about 5 feet. The usual fossils, Trigonia impressa, &c., occur. the lower limestones, 15 and 17, are greenish clay inclusions.

The great mass of buff limestone below the slate is almost unfossiliferous, and neither its mineralogical character nor its few fossils give sure evidence of its relationship to neighbouring beds.

Prominent in the lower half of the section is the breaking up of the calcareous series by small clay beds, and of these No. 23, with its dark compact clays, is in part made up of oyster-shell fragments. It contains numerous compressed shells, Perna quadrata, Nucula, &c., but washings of the beds yield hardly any microzoa. The limestone above the clay yields wellknown Great Oolite shells, Mytilus Sowerbyanus, Rhynchonella concinna, and Ostrea Sowerbyi. The shelly limestone below the clay is in part an Oyster lumachelle, and passes into a blue-hearted limestone with Perna quadrata, large Cyprinc, Corbula, and Macrodon. Here, again, both petrological facies and fauna are dissimilar to any of our known Oxfordshire Oolitic rocks, and, like each of the succeeding lower beds, should be classed as Great Oolite; one of the latter, a hard very oolite freestone, has also as distinctive a character.

In conclusion, it should be stated that though, when Professor Ed. Hull reported to your Association at its Oxford meeting, thirty-four years ago (1860), the presence of seventy feet of Great Oolite limestone under the Stonesfield Slate, it seemed to be an over-estimate, yet the result of the present investigation has been to prove the presence of an important and overlooked section of the Great Oolite, and to entitle place for it in future accounts of that subdivision. That Professor A. H. Green doubted the existence of so great a series of beds as those quoted by Professor Hull is proved by the absence of any account of them in his excellent memoir On the Geology of the Country round Banbury, Woodstock, Bicester, and Buckingham,' published in 1864.

Mr. James Windoes, Mr. Wilfred Hudleston, Mr. H. B. Woodward, and your Secretary have also worked in later years at the determination of the equivalent of these lower Bathonian beds in the neighbourhood of Chipping Norton.

To his Grace the Duke of Marlborough, to the Right Hon. Lord Dillon, to Mr. John Barrett of Stonesfield, and to Mr. S. Shilson of Charlbury, the thanks of your Committee are due for aid in this and other relative work.2

The probable extension of a lower division of the Great Oolite below

'E. A. Walford, Q.J.G.S., vol. xxxix. p. 230.

2 Mr. R. F. Tomes has kindly named the corals.

1894.

Χ

the limit reached by us, large enough with that already discovered to entitle it to a place as a sub formation, makes a continuance of the work a necessity for the right understanding of the lower Jurassic rocks of Great Britain.

Section at the S. W. end of Covert, Stocky Bank, Stonesfield, Oxon, 1894.

1. Humus with limestone fragments containing Nerinæa, Cryptocania Prattii E and H, Cryptocania sp., Isastræa microphylla Tomes, Isastræa limitata Lamx., Isastraa near to limitata Lamx., Thamnastraa Lyelli E and H and Epismilia sp. 'RIFT BED'

Ft. In.

09

2. Grey Marls with Ostrea, Placunopsis, and Rhynchonella concinna 40 3. Fawn-coloured Sands and Marls-oyster bed

4. Grey shelly compact Limestone weathering cream-coloured
5. Hard grey Marls with Rhynchonella concinna
6. Shelly Limestone

7. Marl

8. Limestone

9. Marls with Oysters, &c. .

.9 in. to 1

2 0

6426000

10. Limestone, shelly oolitic and cream-coloured 'Roof' of Slate . 11. Stonesfield Slate, 'Top hard,' compact, grey crystalline 5 in. to 0 12. Soft fissile Sandstone Pendle' 13. Limestone, coarsely fissile and oolitic, with clay inclusions, concretions, black carbonaceous markings and fragments of Rhynchonella and Trigonia impressa

14. Marl, brown fissile and sandy

15. Shelly Limestone, laminated and banded with clay inclusions in the upper part; fawn coloured with Oysters

16. Soft fissile Sandstone with carbonaceous markings

17. Limestone, compact, close-grained, fawn-coloured with carbonaceous markings and clay inclusions

18. Limestone, close-grained, buff-coloured

19. Clay

20. Limestone, compact, buff-coloured

1 3

2 6

1

7

21. Marl

22. Limestone, white, shelly and crystalline, with Mytilus Sowerbyanus, Rhynchonella concinna, and Ostrea Sowerbyi

1 3

23. Black Clay, crowded with Placunopsis in places, with Perna, Nucula, and Ostrea

1 7

24. Shelly earthy Limestone, made up mainly of Oyster fragments, and passing into a brown, blue-hearted Limestone crowded with shells, Perna quadrata, large Cyprina, Corbula, and Macrodon

26. Hard oolitic Freestone, blue-hearted, made up of whitish oolites

Character of the High-level Shell-bearing Deposits at Clara, Chapelhall, and other Localities. (Chapelhall Section.) Report of the Committee, consisting of Mr. J. HORNE (Chairman), Mr. DAVID ROBERTSON, Mr. T. F. JAMIESON, Mr. JAMES FRASER, Mr. PERCY F. KENDALL, and Mr. DUGALD BELL (Secretary).

APPENDIX-On the Chapelhall Clay, by D. ROBERTSON

I. LOCALITY AND PREVIOUS NOTICES.

Page 313

CHAPELHALL is a little mining village situated in the north-eastern part of Lanarkshire, about twelve miles east from Glasgow and two miles south from Airdrie. Its name has been well known to geologists for more than thirty years past from its being usually mentioned in works relating to the science as the highest locality in Scotland where' shelly clay' has been found (510 feet above the sea). That of Clava, near Inverness, which the Committee reported upon last year, is of more recent discovery, and has not been so generally referred to.

་

It may be useful, first, to present a summary of the hitherto existing information regarding this 'deposit.'

(i.) Mr. Smith, of Jordanhill. The 'shelly clay' at Chapelhall was first brought into notice by Mr. Smith, of Jordanhill, in a paper read to the Geological Society in 1850, and republished in his well-known little volume of Researches in Newer Pliocene and Post-Tertiary Geology,' in 1862. The following is the passage referring to this 'deposit: '

'Having been informed by Mr. John Craig, F.G.S., that a bed of shells had been discovered near Airdrie, much higher than any previously found in Scotland, I considered it of importance to ascertain the exact amount of the elevation above the present level of the sea, as well as the species of the shells, and the nature of the deposit in which they are found. Mr. Craig kindly accompanied me to the locality, which is near the Monkland Iron Works, and about fourteen miles to the south-east of Glasgow.

The shelly deposit in question proved to be a bed of the Tellina proxima, Brown (7. calcarea? Linn.), an Arctic species extremely abundant in the Clyde Pleistocene beds overlying the till, and which I had formerly procured from a brick-work in the same neighbourhood.' The shells in the present instance were discovered by Mr. James Russell, an operative miner, in digging a well.'

Mr. Smith then states that he ascertained the elevation of the place to be, on the surface, 524 feet above the sea, which is 'at least 150 feet higher than the highest level at which any shelly deposits have been hitherto discovered in Scotland.' He continues :

The most remarkable circumstance attending the present discovery is that the shells were imbedded in the stratified clay below the till.

'Mr. Russell states that at the depth of 14 feet from the surface, after passing through the till, he came to a bed of brick-clay containing

1 This refers to shells previously stated to have been found by Mr. Craig near Airdrie, at a height of 350 feet. See Researches, &c., p. 17. (The place, an old brickfield, has long been filled up.)

the shells, which were therefore 510 feet above the level of the sea. I could entertain no doubt as to the nature of the superincumbent matter, as that part of it which had been thrown out was left lying at the mouth of the well. It was unquestionably the true till. Indeed, if I had entertained any doubt as to this point, it would have been removed by the discovery of a small granite boulder, which was found about 2 feet above the bottom of the till. The nearest granite rock in that direction (N.W.) is at Cruachan, about sixty miles N.W. of Airdrie.

'I may add that Mr. Russell states that after passing through the shelly bed of brick-clay, he came again to the till, thus proving indisputably what has always been suspected, that there has been more than one deposition of the till or boulder-clay.'1

(ii.) Sir Archibald Geikie.-In the preparation of his valuable memoir on 'The Phenomena of the Glacial Drift of Scotland,' published in 1863,2 Sir Archibald Geikie visited the spot, also under Mr. Russell's guidance. He described it as situated on the crest of a ridge which, rising high above the surrounding country, commands an extensive view across the lower part of the basin of the Clyde. On the water shed of this highlying ridge a well was sunk some years ago, and while the excavations were in progress the shells were found.' Sir Archibald then gives particulars corresponding with those stated by Mr. Smith, adding that the till underneath the shelly clay was 'about 24 feet thick, and lay directly on the Carboniferous strata of the district. The brick-clay at its thickest part,' he continues, 'measured 2 feet 1 inch in depth, but thinned away rapidly on every side, so as to allow the upper and lower till to come together. From a number of additional wells, sunk on purpose, Mr. Russell ascertained that the clay lay in a hollow of the undermost till, and that this hollow measured about 19 feet long by about 5 feet broad. Pits which were dug beyond the boundary of this little trough showed a great depth of the usual till, but without a trace of brick-clay. The shells consisted entirely, I believe, of Tellina proxima. Usually the specimens were broken, but a good many were taken out entire, with both valves together.'3

(iii.) Dr. Crosskey.-About the same time as Sir A. Geikie's visit, or apparently before it (though the account was later in being published), Dr. Crosskey visited the locality, and made some observations which were communicated in a paper to the Geological Society in January 1865. He remarked: 'One of the most perplexing cases in Scotland, upon any theory of the formation of boulder-clay, has been the alleged occurrence at Chapelhall, near Airdrie, of a bed of clay containing Tellina calcarea, intercalated between the masses of true boulder-clay.

'The facts relating to the discovery of these shells have been recorded by Mr. Smith. . . . The present paper will simply examine the question whether the superincumbent matter was, without doubt, the true till.'

After defining what he means by the term 'a compact, unstratified clay, with a large proportion of striated stones, chiefly of local origin,' and stating that the glacial shells in the west are never found within the boulder-clay proper,' but invariably above it,' Dr. Crosskey proceeds: 'Mr. Russell (the original discoverer of the shells) reports that the

'On the Occurrence of Marine Shells in the Stratified Beds below the Till." Op. cit. pp. 139–142.

2 Trans. Geol. Soc. Glas. vol. i. part 2. Quar. Jour. Geol. Soc. vol. xxi.

Ibid. pp. 58-9.