BRICKEARTH AND CLAY- WITH-FLINTS FROM KENT

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1 BRICKEARTH AND CLAY- WITH-FLINTS FROM KENT By P. A. SABINE, B. R. YOUNG and J. DANG~RFI~LD Geological Survey and Museum, Exhibition Road, London. [Received 3rd January, 1963] ABS~CT Particle-size analyses of brickearth and Clay-with-flints from Kent, England, are presented. A calcareous sample of brickearth is comparable to loess. In th~ clay fraction, there is more illite (or glauconite) than kaolin; and there is some chlorite. The clay fraction of the Clay-withflints consists of smectite, illite and quartz and is probably derived directly from the Chalk. Black sand-grade nodules are manganiferous. INTRODUCTION Arising from the primary six-inch geological survey of the district around Canterbury and Folkestone, Kent, a number of specimens of brickearth and Clay-with-flints were collected by Mr J. G. O. Smart. There are few data available on the composition of either of these British deposits, and to help fill this gap this note presents some of the results of the examination of these specimens. The term brickearth is applied to superficial buff, brown, or red deposits, which are essentially fine sands and silts with some clay and are so called as they have long been used for making bricks (Dines, Holmes and Robbie, 1954). The formation which has the same name (Brickearth), occurs mantling Mesozoic and Tertiary strata or other Drift deposits and is mainly of Pleistocene age (Loveday, 1962). The name Clay-with-flints was applied by Hull and Whitaker (186l} to a deposit which caps the Chalk and is mainly of Pleistocene age. It is aptly named. Both the reddish-brown clay and the large flints enclosed by the clay are thought by many authors to have been derived as a residue after solution of the Chalk. Others have challenged this view, and recently Loveday (1962) has reviewed the nomenclature and theories of origin, and described deposits from the Chiltern Hills north of the London Basin. BRICKEARTHS In Table 1 are shown particle-size analyses of the brickearths~ Since the results depend partly upon the analytical methods used, it is necessary to specify them. The field samples were broken up by hand and each one was split until a fraction of suitable size for analysis was obtained. The fraction to be analyzed was broken down further by hand and by use of a rubber pestle, and when necessary by gentle pressure with a ceramic pestle. It was then dry-sieved through a 300-mesh B.S. sieve. Material retained on the 300-mesh sieve was 248

$7 to No. 300) listed in Table 1, using distilled water. A sub-sieve particle-size analysis was carried out by the pipette method on a weighed portion of each < 300-mesh fraction.$

2 BRICKEARTH AND CLAY-WITH-FLINTS 249 placed in a very weak solution of Calgon (sodium hexametaphosphate), warmed and gently stirred to complete dispersion. Next it was washed through the B.S. sieves (from No. 7 to No. 300) listed in Table 1, using distilled water. A sub-sieve particle-size analysis was carried out by the pipette method on a weighed portion of each < 300-mesh fraction. The apparatus used and methods adopted were those described by the British Standards Institution (1948), exc~pt that sodium hexametaphosphate was used instead of sodium oxalate. Figures are expressed to two places of decimals to allow summation to 100 per cent., but the individual results are probably accurate to a smaller number of digits. Dispersed iron oxide is included in the clay fraction and calcite (some extremely fine) is present in one sample (No. 3). Glauconite is common in the medium and fine sand, and perhaps also in the clay fraction. British and other brickearths have been compared with the loess deposits of Europe and elsewhere. Pitcher, Shearman and Pugh (1954), who showed that much of the Pegwell Bay Brickearth (Kent) was a loess, accepted the essential criteria for loess postulated by Russell (1944), including the presence of at least 50 per cent. of particles between 0-05 mm and 0-01 mm in size, and the presence of calcareous tubular concretions often enclosing rootlets. Half the present samples fail these criteria on grain size, and only the cal careous brickearth (No. 3), which has rootlet tubes remaining and has 50 per cent. within these size limits, is closely comparable with loess: the others may be weathered types but the evidence available does not allow decisive argument. The clay fraction of the calcareous sample (Table I, No. 3), wh;ch is rich in calcite, and four others (Nos. 4, 5, 7 and 8) were examined by X-rays in an cm diameter powder camera fitted with a beam trap which enabled spacings up to about 25 A to be recorded with Co Ks radiation. All the samples contain illite (or glauconite), kaolin and quartz, and by visual comparison with patterns of standard mixtures prepared from reference clay minerals* it was estimated that illite is three to four times as abundant as kaoljn. All the samples gave a very weak line at 14 A which remained after heat treatment at 550~ for 2 hours, and is presumably due to a little chlorite. CLAY-WITH-FLINTS The results of particle-size analyses of the matrices of the Claywith-flints samples prepared in a similar way to those of the brickearths, are also shown in Table 1. They reveal the very poor sorting of the deposit and contrast with the results of Loveday (1962). Black nodules, abundant in the sand grades (specimen No. 14) were *The reference minerals used were Fithian illite and kaolinite from Lamar Pit, Bath, South Carolina. Almost certainly the illite (or glauconite) will not have the same composition (and particle size) as the Fithian illite, and for this reason the ratio quoted is to be taken only as a rough guide.

3 250 P.A. SABINE,, B. R. YOUNG AND J. DANGERFIELD TABLE 1--Particle-size analysis B.S. Gravel Sand Classification Fine Coarse Medium Particle diam. mm ~2-411 >1.2(14] >0.599 >0.422 >0.296 >0.211 Meshes to oneinch >7 > 14 >25 >36 >52 >72 Brickearths No.* 1 0' " " Nil ,55 0"59 0" ' " '05 0' Nil 0' " Nil " " " " " " "67 0" ' "11 Clay-with-flints ' , ' * For details of samples see following page.

4 BRICKEARTH AND CLAY-WITH-FLINTS 251 of brickearths and Clay-with-flints. Silt Clay Fraction Fine Coarse Medium Fine '-- > >0.076 >0.053 >0020 >0.006 >0-002 i O-05mm <0.002 (approx per > 1 O0 >200 > 300 < 300 (Sub-sieve) cent.) i ' " ' ' ' " " " "77 8'86 73"80 2'15 2"75 8" "30? 2"02 5,63 37 " '59 25 " '23 1 " ' "16 28" "87 ~ 1" "10 3" "45 2'06 2"76 26" ' ' "43 5" "43 4" "65 41 "47 3 "90 2" ' " "30 1 " " " I " I t Total > 100 mesh.

5 252 P.A. SABINE, B. R. YOUNG AND J. DANGERFIELD TABLE 1--Continued. KEY TO SAMPLES. [The locality is followed by the British National Grid reference (TR--) and the the specimen number in the Geological Survey and Museum. All localities are in Kent.] 1. Brickearth on Woolwich Beds. 275 m (300 yd.) N of White Wall, Dunkirk~ TR M.R Brickearth on Thanet Beds (near Chalk boundary). 415 m (450 yd.) N 74 ~ W of Staple Church. TR M.R Calcareous brickearth on Thanet Beds (near Chalk boundary). 460 m (500 yd,) E 65 ~ S of Wingham Church. T.R M.R Brickearth on Thanet Beds. 370 m (400 yd.) W 40 ~ S of Denstead Farm, TR M.R , 5. Brickearth on Thanet Beds. Road cutting 275 m (300 yd.) E 20 ~ S of Preston Farm. TR M.R Brickearth on Chalk and Clay-with-flints. 90 m (100 yd.) E of Inn at Stelling Minnis. TR M.R Brickearth on Chalk and Clay-with-flints. Hawkinge Brickworks, Folkestone, TR M.R, Brickearth on Chalk. 460 m (500 yd.) E 40 ~ S of Canterbury (South) Station. TR M.R Brickearth on Chalk. 460 m (500 yd.) N 31 ~ W of Petham Church. TR M.R Brickearth on Gault. 735 m (800 yd.) W 40 ~ S of Horton Park. TR ~ M.R Brickearlh on Folkestone Beds. 370 m (400 yd.) E 40 ~ S of Church at Brabourne Lees. TR M.R Matrix of Clay-with-flints. Trench 165 m (180 yd.) S.W. of Wytherling Court, Molash. TR M.R Matrix of Clay-with-flints. 185 m (200 yd.) S.W. of the Inn at Stelling Minnis. TR M.R Matrix of Clay-with-flints. Sewer Trench at Capel Street, S.E. of Couldham. TR M.R Matrix of Clay-with-flints. 275 m (300 yd.) S.W. of the Inn at Stelling Minnis. TR M.R Matrix of Clay-with-flints. 460 m (500 yd.) N 31 ~ W of Petham Church. TR M.R

6 BRICKEARTH AND CLAY-WITH-FLINTS 253 confirmed by spectrographic analyses by K. L. H. Murray to be manganiferous, but as commonly happens with some manganese minerals they yielded only a very poor X-ray pattern. In thin section (No. E 30670) there is no structure discernible in most of the grains, but a few enclose quartz grains. The manganese in these nodules was probably derived from the Chalk, where it occurs in small quantities. Examination of the clay fraction from No 14 showed it to consist of a smectite, illite and quartz. The smectite gives a strong 060, 330 reflection at 1.49 A and by visual comparison with films of standard clay mixtures* is probably montmorillonite. It appears to be present in about the same amount as the illite. That smectite and illite are commonly present in the Middle and Upper Chalk (Perrin, 1957; Avery et al., 1959) has recently been confirmed by examination of Chalk from the Geological Survey's Fetcham Mill Borehole, Leatherhead, Surrey. Clay fractions of residues insoluble in dilute acetic acid (ph 3) from the Middle and Upper Chalk were composed mainly of illite and smectite. In the Lower Chalk, iuite was abundant, kaolin present in all samples, and smectite abundant in the uppermost and lowermost beds but only a minor constituent in the intervening ones. Acknowledgement.--This paper is published by permission of the Director, Geological Survey and Museum. REFERENCES AVERY, B. W., STEPHEN, I., BROWN, G., and YAALON, D. H., J. Soil Sci., 10, 190. BRmSH STANOARDS INSTITtrrION, Brit. Stand., DINES, H. G., HOLMES, S. C. A., and ROBmE, J. A., Geology of the Country around Chatham. Mere. geol. Surv. U.K. HULL, E., and WmTAI~ER, W., The Geology of Parts of Oxfordshire and Berkshire. Mem. geol Surv. U.K. LOV~DAV, J., Proc. Geol. Ass., Lond., 73, 83. PERPaN, R. M. S., Clay Min. Bull., 3, 198. PITCHER, W. S., SHERMAN, D. J., and PUGH, D. C., Geol. Mag., 91,308. RUSSELL, R. J., Bull. geol. Soc. Arner., 55, 1. *The reference minerals used were Fithian illite and Ward's montmorillonite (No. 19) from Polkville Mine, Polkville, Mississippi.

THE USE OF PIPERIDINE AS AN AID TO CLAY-MINERAL IDENTIFICATION

THE USE OF PIPERIDINE AS AN AID TO CLAY-MINERAL IDENTIFICATION By J. M. OADES* and W. N. TOWNSEND Department of Agriculture, The University of Leeds. [Received 30th August, 1962] ABSTRACT It is suggested