1136 THE COLLIERY GUARDIAN. November 29, 1918. KIMMERIDGE OIL SHALE,* By A. Strahan, Sc.D., LL.D., F.R.S. The Kimmeridge clay crops out at intervals in Dorset, Wiltshire. Oxfordshire, Buckinghamshire, Cambridgeshire, Norfolk, Lincolnshire and Yorkshire, and has been proved to exist, at a considerable depth, in parts of Kent and Sussex. The lack of continuity in the visible outcrops is due to the fact that the Kimmeridge day, with the overlying members of the oolitic group, was subjected to denudation, probably at more than one period, before the upper cretaceous rocks were deposited. The area originally occupied by it was cut into and curtailed, and the patchy mode of occurrence which is observable along the margin of the cover of later formations is likely to continue beneath that cover. It has been known for centuries that the Kimmeridge clay contains bands of inflammable shale in Dorset, and for many years that somewhat similar material exists in Norfolk, Lincolnshire and Yorkshire. Until lately, however, no attempt had been made to utilise the material except in Dorset, where a band known as the Blackstone or the ‘‘Kimmeridge coal” has been worked at intervals for use by cottagers as fuel, and has been experimented upon for other purposes. The principal oil shales occur in the upper division of the Kimmeridge clay, but beds containing more or less bituminous matter are not confined to this division or to one horizon in it, for thin and inferior bands occur lower down in the formation near Abbots bury and doubtless elsewhere. That the principal development occurs on or near the same horizon is indicated by the fossils, Saccocoma especially being a highly characteristic constituent. In the oil shales at Kimmeridge and Corton it appears to be confined to a narrow horizon, ranging at Kimmeridge from the Blackstone to a level about 13 ft. below ; and it should prove a useful datum guide in future borings in the Kimmeridge clay. The “ Blackstone,” therefore, is probably the same as the “ Main Bed ” of Corton, and not improbably as the bed observed elsewhere in Dorset. Its distance, however, below the top of the Kimmeridge clay varies considerably. In Kimmeridge Bay the distance is estimated at 556 to 580 ft., between Upway and Abbots- bury at 430 ft., and in Portland Island at 300 ft. The outcrop of “ Blackstone ” in Kimmeridge Bay would be ranging from a few feet to upwards of 300'ft. below the base of the Spilsby sandstone. As regards the area concealed by newer formations, the Kimmeridge clay has been proved in some of the borings made in search of coal in Kent and Sussex. It extends as far north as a line drawn a mile south of Dover, five miles south of Faversham and four miles south of Rochester. North of this line its absence has been proved in all the borings in Kent and Middlesex and in the borings at Streatham and Richmond in Surrey. At a boring at Little Missenden in Bucking- hamshire the record was too imperfect to show whether the Kimmeridge clay was present or not. It was absent at Ware, near Hertford, but it may have been present in the boring at Saffron Walden in Essex. On the other hand, it was absent at Culford and Lowestoft in Suffolk, at Harwich in Essex, and in the borings in and east of London. As regards the south of England, nothing is known of it between the boring at Penshurst in Kent and the outcrop in Dorset. From the results of various borings, it appears that the north rn limit of the Kimmeridge oil-shale field of Sussex must run south of Dover, Brabonrne and Pluckley, but north of Penshurst and Battle. The absence of bituminous beds towards the north is asso- ciated here, as in Oxfordshire and Berkshire, with attenuation of the formation as a whole. The bitu- minous matter, which is wholly of animal origin, was concentra’ed, or perhaps escaped removal, only in the deeper parts of the Kimmeridge sea, not towards its margins—the reverse of what takes place in the case of lignites and other drifted materials of vegetable origin. Uses and Values. Methods of utilising the oil in the bituminous bands of the Kimmeridge clay have been under consideration for many years. In 1848 the Bituminous Shale Company erected works at Weymouth, and produced varnish, lubricating grease, naphtha, pitch and paraffin wax. In 1854 the company was wound up, and Messrs. Ferguson and Muschamp took over the property for the purpose of preparing a manure from the shale. It was stated that a ton of the shale produced 74 gals, of naphtha, 10 gals, of lubricating oil, 1 cwt. of pitch and 114 cwt. of residue, together with some fine white paraffin wax and gas. In 1858-186- a company con- sisting chiefly of French gentlemen drove several adits, In the Kimmeridge holes Nos. 1 and 2 the shales of interest commence about 60 ft. where a section known as the “ Short Joint ” was passed through. This section has a thickness of about 10 ft. and an oil value of 14 gallons per ton. Below the “ Short Joint,” clays and inferior shales alternate for 20 ft., until the “ Blackstone ’ is jeached. This is a well-defined bed, from 2 ft. to 2 ft. 6 in. in thickness, and averages for the three holes 37’6 gallons of oil per ton; sulphate of ammonia, 28 6 lb. per ton. The “ Rudicum ” section lies about 5 ft. below the “ Blackstone.” It is under 2 ft. in thickness, of which about 1 ft. is of inferior shale. The tube tests gave 22*6 gallons of oil per ton; sulphate of ammonia, 18 4 lb. per ton. On the assumption that in mining the Blackstone a thickness of the overlying inferior shale sufficient to make up a total of 4 ft. would also be ra:sed, the extraction was estimated at 284 gallons of oil per ton and 234 lb. of sulphate of ammonia per ton. The examination in the laboratory of specimens from the boreholes, etc , gave yields of od varying from 13’9 to 40'5 gals, per ton, and 11'8 to 32’4 lb. of sulphate of ammonia per ton. The yield of oil in these results falls far short of the estimates and statements made by Mr. Heyl and Mr. Manfield, who asserted that by their method of distillation they secured from Corton shales a yield of 40 gallons of oil per ton and over when working a thickness of upwards of 4 ft. From a report furnished by Mr. A. C. V. Berry to the Ministry of Munitions in February 1918 it appears that the oil distillate from the Main Bed in Corton No. 2 borehole contains 7'20 per cent, sulphur; that from the “Blackstone ’’ of Kimmeridge No. 1 borehole, 6'16 per cent, sulphur; and that from the “ Short Joint” section of the same hole (at a depth of 65 ft.), 5'12 per cent, sulphur. In reporting on methods of opening out a mine at Kimmeridge, Mr. Joseph Stevenson suggests the sinking of shafts about 4,700 ft. east of No. 3 borehole. The area recoverable would be 1,900 acres, with an additional 1,000 acres on the deep side, obtainable by extending levels in a northerly direction. The dip is estimated to be 1 in 30, in a direction E. 10 N. The estimate of the amount of Blackstone and of the over- lying shale-bed, 1 ft. 11 in. thick, recoverable from this INDEX PORTLAND BEDS KIMMERIDGE CLAY 'COAL' CROP £ Cj • • • • i ' WORTH WEALDEN BEDS ANO Map of Kimmeridge Clay Outcrop FPOM ABBOTSBURY TO — UPWAY junction’ BURNING CLIFTj H/mmeridqeI Mam 0il-8haie CLAY I WEALDEN BEOS ANO PURBECK BEDS t POXWELlJ I Fig. 1.—Map of the Kimmeridge Clay Outcrop near Kimmeridge. Fig. 2.—Map of Kimmeridge Clay Outcrop from Abbotsbury to Burning Cliff. the natural outcrop for gas or liquid petroleum if any existed. It is situated not only on the crest of an anticline, but in the region where that crest attains its greatest elevation. Neither gas nor oil has been observed. Having regard to the fact that the principal oil- shales occur in the upper part of the Kimmeridge clay, they must not be assumed to exist in all the outcrops of that formation. In some the upper division is missing, owing to the unconformable superposition of later formations; in others it is present but concealed. There is also reason to believe that the oil shales were never developed as such, over much of the distance between Dorset and Cambridgeshire, for they have not been found in normal form even in those outcrops where the upper division is present. As a fact, the Kimmeridge clay as a whole becomes greatly attenuated in the central parts of England, and it is only in the more normal developments to the north of that area that the oil-shales re-appear, and there only in degenerate form. In Dorset, the thickness of the Kimmeridge clay has been estimated at 900 ft. In Wiltshire and the adjacent part of Dorset the whole formation, with the overlying Portland beds, crops out, but there is no record of the occurrence of oil shale. In Oxfordshire and Berkshire, where the Hartwell clay forms the highest member of the Kimmeridge clay, the thickness has been estimated at 100 to 60 ft. Shale containing a mere trace of oil has been noticed in excavations for the Great Western R lilway bridge over the Thames, near Abingdon, but the fossils suggested that the shale occurred near the top of the lower division of the Kimmeridge clay. In Buckinghamshire, where also the upper beds include the Hartwell clay, the thickness is not known. In Cambridgeshire the upper division is known for a thickness of 15 ft,, but its top is not seen. The lower division is estimated to be 80 to 90 ft. thick. Traces of bituminous shale occur in Roslyn Hole, near Ely. In Norfolk, the existence of bituminous shales at Southrey was recorded in 1835. Farther north, near King’s Lynn, are the recent explorations described later, In Lincolnshire and Yorkshire the bituminous shales have been recognised at such frequent intervals as to suggest th it they are continuous wherever the Upper Kimmeridge division exists. The thickness of the Kimmeridge clay in Lincolnshire is estimated at 320 ft., but the upper- most beds are missing, having been denuded away before the Spilsby sandstone was deposited. Thin bituminous shales have been observed at horizons * From Special Reports on the Mineral Resources of Great Britain, Vol. vii„ Part I. and exp >rted the shale to various parts of the world. This was followed by the Wareham Oil and Caudle Company, and later on, from 1872-1876, by Messrs. Emmens. The Sanitary Carbon Company wus then formed, with a view to producing a sanitary agent from the residual coke, with properties resembling those of animal charcoal. It was succeeded by Messrs. De Grelle and Company in 1879, and afterwards by the Kimmeridge Oil and Carbon Company, who established works at Sandford, near Wareham. With regard to the occurrence of bituminous shale near Portisham, about 1884, a shaft was sunk, and 109 tons or more of shale was sent to Scotland to be retorted. The result did not indicate that a remuner- ative price could be obtained. In 1903 a quantity of shale was sent to Scotland, and, though the yield of oil and sulphate of ammonia was regarded as satisfactory, it was found that the high sulphur content would have to be reduced before the oil would be saleable. In the evidence before the Royal Commission, it was stated by Sir Boverton Redwood that it had been estimated that there were over 1,500,000 tons of shale, yielding about 50 gals, of oil and 38 lb. of sulphate of ammonia to the ton. He referred to the fact that the oil has an offensive odour and is difficult to refine; and Sir George Beilby confirmed .the earlier unfavourable reports. The revision made in 1912 of the Admiralty specification for oil fuel, whereby the proportion of sulphur permissible was raised from 0'75 per cent, to 3 per cent, led to the renewal of attempts to reduce the sulphur-content of the Kimmeridge product, but hitherto without success except at a prohibitive cost. Reduction to the stipulated 3 per cent, has been effected only by mixing in other material of low sulphur- content. The oil obtained by retorting Kimmeridge shales contains fiom 6 per cent, to 7 per cent, of sulphur. The extent and value of the Kimmeridge oil shale in Dorset and Lincolnshire was made the subject of inves- tigation by the Department for the Development of Mineral Resources (Ministry of Munitions) in the years 1917-18. The following account of the research in Do set has been summarised from a report bv Mr. W. T. Anderson, Chief Technical Adviser, by permission of Sir L. Phillips. Controller. In August 1917 the boring of a series of holes near Kimmeridge and Corton was commenced. The positions of the holes are indi- cated on the accompanying maps (figs. 1 and 2). Boreholes Nos. 1, 2 and 3 at Kimmeridge showed beds of 2 ft. 6 in., 2 ft. 24 in., and 2 ft. 24 in. thick respectively, and Nos. 1, 2, 3a and 4 at Corton beds respectively, 2 ft., 2 ft., 1 ft. 9 in. and 2 ft. 1 in. thick. area of 2,900 acres is 23 million tons, furnishing 455 million gallons of oil, and 250,850 lb. of sulphate of ammonia. In the Corton area the dip is northwards, at an angle of 15 degs. 15 min , and the driving of inclines in the Main Bed, from the outcrop to the Ridgeway Fault (fig. 2) is suggested. On the supposition that an area of 1,500 acres would be recoverable, the amount of shale is estimated at 32 million tons, with 442 million gallons of oil, and 183,000 lb. of sulphate of ammonia. The specimens obtained by the Ministry of Munitions from their boring at Donnington-on-Bain were found on analysis to yield 1'3 to 16'4 gals, of oil per ton of dry shale. The sulphur-content of oil obtained from tube- test of two of the samples was 3‘89 per cent. Occurrences. In Dorset there are four separate outcrops of Kimmeridge clay, and in all of them the existence of bituminous shales has been recognised. The following account takes the-e outcrops in order from east to west:— Kimmeridge.—In this bay were situated the earliest, and for many years the only, workings in the Kimmeridge “coal.” Cement from some of the argil- laceous limestones and alum were also made. The outcrop is illustrated by the map forming fig. 1. It is traversed by an anticline, which ranges nearly east and west, and the crest of which passes a little north of Worth, through Swyre Head to the shore in Kimmeridge Bay. At its eastern end the anticline takes the form of a gentle arching up of the strata, but in Kimmeridge Bay it is a more pronounced fold, marked by a greater elevation of the strata and with dips ranging up to 16 dcgs. and 20 degs. in its northern limb. In pro- ceeding westwards along the shore from the eastern end of the outcrop, a descending section in the Kimmeridge clay is crossed, and in more than two miles further on, after passing over a thickness of beds esti- mated at 550 to 580 ft., the bituminous beds emerge from beneath the foreshore. At Clavell’s Hard, 200 yds. east of the emergence, the well-known “ Blackstone” or “ Kimmeridge coal,” has been worked by levels in the face of the cliff. Rising at an average gradient of 1 in 24, the outcrop gains the top of the cliff 3,700 ft. west of the point where it first emerges, and then passes inland, where it has been opened up, in past times, in small slants and pits. All these are situated on the south side of the anticline and between where they cease and the village of Kimmeridge, runs the crest of the fold. In the northern flank of the fold the outcrop must run nearly east and west with a dip to the north, but it has not been explored, probably for a reason which appears on examinatian of the cliff west of Kimmeridge Bay.