April i8, 1872] 



NA TURE 



491 



Coal Measures causing this difference, and rising in the midst 

 of the unconformable newer strata. This shows that in the 

 English Chalk area we may possibly find irregular old surfaces of 

 this kind, so that the Coal Measures may exist at places nearer 

 the surface than we have estimated. 



We have alluded before to the great length and narrow width 

 of the Belgian coal-fields. That of Liege is forty-five miles 

 long, witli a mean width of less than four miles, whilst that of 

 Hainaut and Valenciennes is 119 miles long, with a width 

 scarcely greater. The presence of lo«'er Carboniferous rocks 

 under Harwich, and the wider range north and south of the 

 Bristol coal-field, renders it possible that the trough in the inter- 

 mediate area may have a greater expansion than in Belgium ; 

 but we have nothing else to guide us. unless it be that the lateral 

 pressure in the intermediate ground was probably less than in 

 the Ardennes and the Mendips, where it has exercised its maxi- 

 mum elevatory force. In that case the coal-trough in tliis inter- 

 mediate area would be les j compressed and more expanded ; so we 

 might consequently here look to find larger coal-basiusthan either 

 those of Somerset or Liege. The position of these basins I am 

 disposed, for reasons given in my Report, to place farther north 

 than Mr. Godwin-Austen, and should therefore look for them not 

 in the valley of the Thames, or on the line of the North Downs, 

 but under South Essex, Middlesex or Hertfordshire, Oxford- 

 shire, and North Wdtshire. 



The strata on the south side of the Liege coal-field rise abruptly 

 against highly inclined and faulted Devonian rocks, and the 

 north side they rise at a less angle beneath Cretaceou; or Ter- 

 tiary strata. In the Hainaut coal-field the overlying have a 

 greater extension. Under these strata the Coal Measures are 

 succeeded by the Mountain Limestone, and then by Devonian or 

 Silurian strata; but with one or two limited exceptions their 

 outcrop is hidden by the newer strata which stretch uninter- 

 ruptedly northward over the rest of Belgium. The Palaeozoic 

 strata have, however, been met wifh near Brussels, under 

 Tertiary strata, at a depth of about 600 feet, and at Ostend at a 

 depth of 9S5 feet, of which 682 consisted of lower Tertiary 

 strata, 210 feet of Chalk, and 93 of coloured marls. It appears, 

 therefore, not improbable, that tlie Tertiary and Cretaceous 

 strata of all Belgium may repose directly on a floor of Paleozoic 

 rocks ; and as there is reason to suppose that all these rocks have 

 a strike parallel with that of the Ardennes, folds in the strata 

 may bring in some under-ground coal-basin or basins in parallel 

 lines to the north, in the same way that small troughs of Coal 

 Measures are brought in again in the Ardennes to the south of 

 the great coal-trough. On the other hand, the great Palaeozoic 

 axis of the Ardennes, consisting of Silurian and Devonian rocks. 

 Mountain Limestone, and Coal Measures, passes westward under 

 the Chalk of the north of France, and has been followed under 

 gi-ound as far as to Calais, where it lies at adepth of 1,032 feet ; 

 while in the direction of Boulogne it keeps nearer the surface, 

 outcrops from beneath the Chalk downs surrounding the Boulon- 

 nais, and disappears westward under an unconformable series of 

 Jurassic and Wealden strata. 



We may, I think, look for a prolongation of this old Palaeo- 

 zoic surface of highly inclined, contorted, and faulted rocks at 

 no very great depth under the same Wealden, Chalk, and 

 Tertiary area of the south of England. For, although the old 

 Palaeozoic surface descends rapidly from about 300 feet above the 

 sea-level in the Boulonnais to 1030 feet below it at Calais, it 

 rises at Ostend 47 higher than at Calais, and crossing the 

 Channel, it is found at Harwich within a few ffet of the same 

 depth as at Calais, from which it is eigliiy miles distant in a 

 northerly direction. Passing westward from Calais, we find 

 the Palaeozoic rocks under London 105 miles distant, and 102 

 feet higher than under Calais, and 106 feet higher than at 

 Harwich. Allowing for irregularities of the old surface as 

 evinced by the well at Crossness, near Plumstead, which was 

 still in the Gault at a depth of 944 feet, or some 14 feet below 

 the level of the Palccozoic rocks at Kentish Town, we may still 

 consider that in the area between these three points, and pos- 

 sibly throughout the south-east of England, the Palaeozoic rocks 

 will probably be found not to be more than from 1,000 to 1,200 

 feet beneath the sea-level. 



Projecting the line another 100 miles westward, we reach the 

 neighbourhood of Bath and Frome, where the Coal Measures 

 are, as before mentioned, lost at a depth of about 450 feet, 

 beneath Liassic and Jurassic strata. In the intermediate area 

 between that place and London no trial-pits and no wells have 

 b?en carried to a depth of anything like 1,000 feet beneath the 



sea-level. The deepest well with which I am acquainted is one 

 near Ch ibham, in Surrey, through Tertiary strata and Chalk 

 to a depth of about 800 feet, or of 550 leet beneath the sea-level. 



There are, however, in all this area certain indications of the 

 proximity of old land and of pre-Cretaceous denudation, in the 

 presence of qurrtz and Lydian pebble-stones, accompanied by 

 Secondary ro^k fossils in the Lower Greensaiids of Surrey, and 

 in the like old rock pebbles, with the additim of slate pebbles, 

 in that formition in North Wiltshire ; while the banks of shingle, 

 Bryozoa, and sponges of the same age at Farringdon, point to 

 still and sheltered waters, probably of no great depth, and to 

 adjacent dry land. Again, on the north of London, we have in 

 the Lower Greensand of Buckinghamshire and Bedfordshire 

 shingle beds consisting almost entirely of fossils derived from 

 Jurassic strata, with a remarkable collection of larger quartz, 

 quartzite, and other rock-pebbles, derived probably from the old 

 Palaeozoic axis. 



On the south also of the great Mendip and Ardennes axis 

 coal strata may possibly be found just as they are found on both 

 sides of the Pennine chain ; for in either case the measures are 

 cut off and broken through by these chains of hills. In South 

 Wales certain folds of the older strata seem to render it probable 

 that tlie Coal Measures may pass under the Bristol Channel, 

 forming a trough wliich prolonged eastward would pass along the 

 south side of the Mendips'. Trials in the latter area, have, how- 

 ever, shown that the New Red .Sandstone, Lias, and Oolitic series 

 attain an infinitely greater thickness than on the north flank of 

 that range, so that it is not likely that the Coal tMeasures would 

 lie at a less depth than from 1,500 to 2,000 feet. 



On further consideration ot the subject, it seems to me a 

 question whether we should not take a still bro.ader view of 

 this great east and west axis, and assign to it a width varying 

 from thirty to eighty miles or more, looking at the Mendips and 

 Exmoor hills as the bounding flexures north and s mth of the 

 same line of disturbance in .Soutii-western England, while the 

 ridges of the Ardennes, the Eifel, and the Hundsruck (in part ?) 

 are exhibitions of the same parallel series of anticlinals. In that 

 case the great coal-basins of South Wales and Somerset would 

 represent the synclinal trough on one side of the axis of dis- 

 turbance, and on the other side we should have the Lower Calr- 

 boniferous or Coal Measures of Devon ; while on the Continent 

 the deep, narrow synclinal trough of the Liege and Aix-la- 

 Chapelle basin may be considered as lying on one side of the 

 arch, and the great coal-basin of Saarbruck on the other. This 

 important coal-basin has already been followed under the New 

 Red Sandstones of the Vosges for a distance of from twenty-four 

 to thirty miles in the direction of Metz, still on the strike of the 

 Ardennes. Further westward, a trial for coal near Doncherry 

 led to the discovery of Palaeozoic rocks, at a depth of 1,090 feet 

 under that thickness of Lias and Infralias ; but the line of the 

 coal-trough should, I think, pass a few miles to the south of this 

 spot. Thence this underground coal-trough would range in an 

 irregular east and west line, keeping parallel, or nearly parallel, 

 with the Mons and Valenciennes troughs, under the north of 

 Champagne, Normandy, the Channel, between the Isle of Wight 

 and Cherbourg, Dorset, and cropping out again in North Devon. 

 The only deep sections that I know of on this line are those 

 furnished by a well sunk many years since, nine miles east of 

 Dieppe, to a depth of 1,092 feet in the Kimmeridge clay and 

 other strata ; and another by a boring at .SotteviUe, near Rouen, 

 through a thin capping of Cre'aceous strata, to a depth of 1,050 

 feet in the same Kimmeridge clay — in either case without reach- 

 ing the Palaeozoic rocks. At Paris no Palaeozoic rocks have been 

 reached at a depth of 2,000 feet. 



In this country the newer strata, overlying the Palaeozoic rocks 

 on our presumed anticlinal line, have been sunk through, with- 

 out result, in the lowest beds of the Wealden at Hastings to a 

 depth of 4S6 feet, in the upper beds at Earlswood, nearReigate, 

 to a depth of about 900 feet, and, on the presumed synclinal 

 line of Carboniferous rocks, through Chalk at Chichester, to a 

 deptli of 945 feet, and at Southampton, through Tertiary strata 

 and Chalk to a depth of 1,317 feet. 



To the south of all the area we have now described, there 

 existed during the Carboniferous period, the ranges of the older 

 Palaeozoic strata of the Hunsdruck andVosces — ol the old crystal- 

 line rucks of Central France, fringed on the east and north with 

 small outlying coal basins of the old Palaeozoic rocks of Brittany — 

 and of the Silurian rocks of South Cornwall — forming the old 

 land-surface, fringed by the great coal-growths subtended north- 

 wards throusjh Northern France, Western Prussia, Belgium, and 



