NATURE 



[July 31, 1890 



turbed. He concludes, further, that the coal-fields which 

 now lie buried beneath the newer rocks are probably- 

 equal in value and in extent to those which are exposed 

 in Somerset and South Wales on the west, and in Belgium 

 and France on the east. 



We will now proceed to test these theoretical conclu- 

 sions by the light of recent observations. 



(6) The coal-fields of Somerset and Gloucester were 

 .proved by the labours of Prof Prestwich and the Coal 

 Commission of 1866-67 to be small fractions of the great 

 coal-basin which lies buried beneath the Triassic, Liassic, 

 and Oolitic rocks, from the Mendip Hills northwards 

 past Bristol to Wickwar. On the west also three small 

 isolated coal-basins occur — those of Nailsea and Portis- 

 head, which are partially, and that of Aust, which is 

 wholly, concealed by the newer rocks. The coal-mea- 

 sures are folded and broken, and traversed by great 

 " overthrust " faults, which at Kingswood give the same 

 series of coals twice over in the sinkings of one colliery. 

 Their southern boundary is the line of the Mendip Hills. 

 They also probably occur at a depth which remains to be 

 proved, still further to the south, in the valley of the 

 Axe and the district of Glastonbury, the most southern 

 boundary being the mountain limestone of Cannington, 

 near Bridgwater. The great Somerset and Gloucester 

 field may extend to the east under the newer rocks, 

 between Freshford and Beckington, in the district south 

 of Bath, 



The value of the evidence of the coal-fields of the 

 west of England on the general question consists in the 

 fact that they may be taken as fair samples of those 

 which lie concealed along the line of the buried ridge 

 through South-Eastern England in the direction of France, 

 Belgium, and Germany. 



(7) One of these concealed coal-fields has been struck 

 in a deep boring at Burford, near Witney, in Oxfordshire, 

 at a depth of 1184 feet, under the following rocks : — 



Oolites ... 

 Lias 

 Rhsetic 

 Triassic rocks 



Feet. 

 148 

 598 

 10 

 428 



The sandstones and shales of the coal-measures were 

 penetrated to a depth of 225 feet (De Ranee, Manch. 

 Geol. Soc, March 26, 1878). 



These coal-measure rocks form, as suggested by Hull, 

 one of the same series of coal-basins as those of South 

 Wales and the Forest of Dean, and probably mark the 

 line of the continuation of the South Wales syncline in 

 the direction of Harwich, where Carboniferous shale has 

 been struck at a depth of 1052 feet from the surface. 



This boring proves not merely the presence of coal- 

 measures at a workable depth in Oxfordshire, but also 

 the important fact that the Triassic rocks, which are of great 

 thickness further north, have dwindled down to an unim- 

 portant thickness in their range southwards and east- 

 wards. Further, that south, in the London area, these 

 rocks are wholly absent ; and farther to the east, at 

 Harwich, the Liassic and Oolitic strata and Lower 

 Greensand are absent, and the Gault rests on the eroded 

 Lower Carboniferous rocks, inclined at a high angle. 



(8) The water-worn surface of the folded rocks, which 

 are older than the Carboniferous, has been repeatedly 

 struck in deep borings for water in the neighbourhood of 

 London, at depths ranging from 839 feet at Ware to 1239 

 feet at Richmond. They consist of Silurian strata in the 

 north at Ware, and of Old Red Sandstone or Devonian 

 rocks in the other localities. From their high angle of 

 dip, as in the case of similar rocks underlying the coal- 

 fields of Somerset and Northern France and Belgium, it 

 may be inferred that coal-fields lie in the synclinal folds 

 in the neighbouring areas. 



From the fact of the Silurian rocks being in the north, 



NO. 1083, VOL. 42] 



while all the rest of the borings to the south terminate ir> 

 the Devonian or Old Red rocks, it may be inferred that 

 the chalk of the North Downs probably conceals the coal- 

 measures. It must also be noted that there are no 

 Wealden rocks in the London area, and no Lower Green- 

 sands, and that the Lower Oolites at their thickest are 

 only 87 feet. The secondary rocks, which are of great 

 thickness in the midland and northern counties, thin off 

 as they pass southwards towards London, against the 

 ridge of older rocks, as both Austen and Prestwich have 

 pointed out. 



It is therefore in the area south of London, rather than 

 in that immediately to the north, that the coal-measures 

 are to be looked for at a workable depth beneath the sur- 

 face, and underneath the chalk of the North Downs. It 

 must, however, be noted that the line of the South Wales 

 syncline through Burford passes to the north of Ware,, 

 and that there may be coal-measures in the northern 

 parts of Essex and of Hertfordshire at a workable depth. 



(9) The Report of the Coal Commission was published 

 in 1 87 1, and in the following year the Sub-Wealden Ex- 

 ploration Committee was organized by Mr. Henry Willett, 

 to test the question of the existence of the Carboniferous 

 and pre-Carboniferous rocks in the Wealden area by an 

 experimental boring. The site chosen was Netherfield,. 

 about 3 miles south of Battle, in Sussex, where the lowest 

 rocks of the Wealden formation constitute the bottom of 

 the valley. The rocks penetrated were as follows : — 



Section of Netherfield. 



Purbeck strata... 

 Portland strata 

 Kimmeridge clay 

 Corallian strata 

 Oxford clay 



Feet. 



200 



57 



1073 

 515 

 60 



1905 



This boring showed that the coal-measures and older 

 rocks are, in that region, more than 1900 feet from the 

 surface of the ground. We may also infer, from the fact 

 of the bottom of the bore-hole being in the Oxford clay, 

 and from the known thickness of the Bath Oolitic strata 

 in the nearest places, that it lies buried beneath consider- 

 ably more than 2000 feet of newer rocks. With this 

 valuable, though negative result, the Sub-Wealden ex- 

 ploration came to an end. It was a purely scientific 

 inquiry, paid for by subscription, and largely supported 

 by those who had no pecuniary interest in the result. 



The experience of the boring at Netherfield showed 

 that the search for the coal-measures and older rocks of 

 Godwin-Austen's ridge would have to be carried out at 

 some spot further to the north, in the direction of the 

 North Downs. In the district of Battle the Oolitic rocks 

 were proved to be more than 1700 feet thick, and the 

 great and increasing thickness of the successive rocks of 

 the Wealden formation above them, which form the sur- 

 face of the ground between Netherfield and the North 

 Downs, rendered it undesirable to repeat the experiment 

 within the Wealden area proper, where the Wealden 

 rocks presented a total thickness of more than 1000 feet, 

 in addition to that of the Oolites. My attention, there- 

 fore, was directed to the line along the North Downs, 

 where Godwin-Austen believed that the Wealden beds 

 abruptly terminated against the ridge of coal-measures 

 and older rocks, and where, therefore, there would be a 

 greater chance of success. 



(10) The evidence, also, of the French, Belgian, and 

 Westphalian coal-fields pointed in the direction of the 

 North Downs. 



The Carboniferous and older rocks, which we have 

 hitherto traced only as far as the area of London from 

 their western outcrops in Somerset, Gloucestershire, and 

 South Wales, reappear at the surface in Northern France, 



