?86 



NATURE 



^August i8, 1904 



approach we may notice in the first place that the subsidiary 

 axes which form the northernmost part of the Devonshire 

 disturbance in South Wales die away one after the other 

 towards the east. Thus an east and west disturbance at 

 Llanelly runs a few miles and disappears. The more 

 important Pontypridd anticline, which traverses the centre 

 of the coalfield, fades away near Caerphilly, while the 

 coalfield itself terminates a little further east, its place on 

 the same line of latitude being taken by the Usk anticline, 

 which trends southwards and south-westwards. So far it 

 might be inferred that the east and west folds die away on 

 approaching the north and south iVIalvernian a.xis. But 

 the Cardiff anticline, which lies south of and was more 

 energetic than those mentioned, crosses the Bristol Channel 

 and, emerging on the other side in a complicated region 

 near Clevedon and Portishead, passes to the north of 

 Bristol and holds its course right across the coalfield at 

 Mangotsfield. The coalfield, however, lies in what is part 

 of the .Malvernian disturbance, for it occupies a syncline 

 running north and south along the west side of the main 

 axis of upheaval. Though the interruption is local and 

 the strata recover their north and south strike to the south 

 of it, yet the east and west a.xis obviously holds its course 

 right through the Malvernian structure. 



Still further south in the direction in which the east and 

 west movements graduallv increase in energy a series of 

 sharp folds is well displayed in the const of South Wales 

 and in an island in the Bristol Channel, ranging for that 

 part of the east and west disturbance which is known as 

 the Mendip axis. This name has been applied to a series 

 of short anticlines which are arranged en echelon along a 

 line ranging east-south-east, but each of which runs east 

 and west. .Among them we mav distinguish the Black- 

 down anticline, the Priddy anticline, the Penhill anticline, 

 north of Wells, and the Downhead anticline, north of 

 Shepton Mallet. With one exception they all die out east- 

 wards after a course of two to ten miles, but the Down- 

 head anticline holds its course into the Malvernian dis- 

 turbance, the two engaging in a prodigious melie south 

 of Radstock. From that much shattered region the Down- 

 head anticline emerges, but the Malvernian axis is seen 

 no more, and. so far as can be judged under the blanket 

 of Secondary rocks, comes to an end. 



Mention has been made of the fact that many of the 

 subsidiary east and west folds die away on approaching the 

 Malvernian axis. In a general way we may attribute their 

 disappearance to the influence of the north and south move- 

 ment, for it is commonly to be observed in these great 

 belts of disturbance that they are composed of a number 

 of parallel anticlines or elongated domes of upheaval, con- 

 stantly replacing one another ; it is a common feature also 

 that these subsidiary folds replace one another not exactly 

 in the direction in which they point, but that they lie en 

 Echelon along a line slightly oblique tn it. The behaviour 

 of the South Wales and Mendip folds is in accordance with 

 these observations, and may be taken to indicate that the 

 effects of the east and west disturbance reached further 

 north in .South Wales than they did in Somerset, or, in 

 other words, that thev failed to penetrate as far into the 

 region where north and south movements were in progress 

 as in the region where there were no movements of that 

 direction. 



The fact that the east and west folds keep their course 

 across the north and south wherever the two actually meet 

 comes out prominently, and supports the inference that they 

 dominate the structure of the Pal.Teozoic rocks which lie 

 hidden beneath the Secondary rocks of the south and south- 

 east of England. Somewhere under this blanket of later 

 formations the east and west axis presumably intersects 

 the other disturbances which traverse the Midlands. To 

 ascertain where and how the intersections take place will 

 be going far towards locating any concealed coalfields 

 which may exist ; but the knowledge can be obtained only 

 by boring, and the number of such exolorations as vet 

 made is wholly insufficient. The majority have been 

 made in search of water, and have been stopped as soon as 

 a supplv was secured. Near Northampton the older rocks 

 were reached at a small depth on what Is believed to be the 

 underground continuation of the Chninian axis, and n 

 borine at Bietchlev traversed what is thoug-ht to have bc-- 

 a great boulder of Charnian rock, suggesting that the axis 



NO. 18 I 6, VOL. 70] 



is not far off ; but with these exceptions the counties of 

 Oxford, Buckingham, Bedford, Huntingdon, Cambridge, 

 and Norfolk are unknown ground. Yet under these 

 counties the axes must run if they keep their course. 

 Where exposed at the surface each post-Carboniferous 

 syncline between two a.xes contains a coalfield. It remains 

 to future exploration to ascertain whether similar condi- 

 tions hold good under the Oolitic and Cretaceous areas of 

 Central England. 



In speaking of the north and south disturbances I have 

 in more than one case stated that the post-Carboniferous 

 movement was but a renewal of activity along an old line 

 of disturbance. The fact is proved by the unconformities 

 visible among the pre-Carboniferous rocks, and it is 

 important for the reason that the geography of this part 

 of the globe at the commencement of the Carboniferous 

 period had been determined by these movements. It has 

 long been known, for example, that the parts of the 

 counties of .Stafford, W^arwick, and Leicester traversed by 

 the axes of upheaval were not submerged till late in the 

 Carboniferous period. On the other hand, some of the 

 area lying immediately west of the Malvernian axis was 

 submerged at an earlier date, as is shown by the existence 

 of Carboniferous Limestone at Cleobury Mortimer and, in 

 greater development, in the Forest of Dean. The borings 

 near Northampton also proved the presence of Carboniferous 

 Limestone, a fact which is in favour of the occurrence of 

 concealed coalfields, in so far as it indicates that the whole 

 Carboniferous series may have once existed there. It is 

 remarkable that none of the borings in the south and east 

 of England have touched Carboniferous Limestone, all 

 having passed into older or newer rocks. The existence 

 of that formation is neither proved nor disproved. 



The determination of the age of these disturbances and 

 a discussion of the pre-Carboniferous geography may seem 

 at first sight to be only of scientific interest, but that 

 problems of great economic importance are involved has 

 been shown recently. It has long been known that the 

 principal coal-seam of South Staffordshire deteriorates west- 

 wards as it approaches the pre-Carboniferous ridge evidenced 

 in the neighbourhood of Wyre Forest. There seemed, how- 

 ever, to be no theoretical reasons why it should not keep 

 its characters on either side of the fault which forms the 

 western boundary of the .South Staffordshire Coalfield, in- 

 asmuch as that fault came into existence after the deposition 

 of the Coal Measures. .\ shaft recently sunk has proved 

 the correctness of the inference. The seam has been found 

 to be well developed to the west of the fault, and a consider- 

 able addition has been made to our productive coalfields. 



So much has been written about the range of the Devon- 

 shire disturbance under the south of England that I shall 

 add no more than a brief comment on some of the evidence 

 on which reliance has been placed. We have seen that 

 there has been some post-Triassic movement along old lines 

 of disturbance in North Wales and the Midlands and along 

 the Malvern axis. It is suggestive therefore to find that 

 in the region which we believe to be underlain by the east 

 and west disturbance, east and west folding forms the 

 dominant structure of the Secondary and Tertiary rocks. 



The anticlines of the Vales of Pewsey and Wardour, the 

 London syncline, the Wealden anticline, the Hampshire 

 syncline, and the anticline of the Isles of Wight and Pur- 

 beck, not only lie in the range of the axis, but show an 

 increasing intensity southwards, towards what we may 

 suppose to have been the most active part of that axis. A 

 similar structure prevails in the Oolitic rocks also. They 

 too had been thrown into east and west folds before the 

 Cretaceous period, and this earlier set of movements also 

 grew in intensity towards the south. It would seem then 

 at first sight that the structure of the later rocks gives an 

 easy clue to the structure of the older rocks buried beneath 

 them. This is by no means the case. That the movements 

 manifested in the Oolitic and Cretaceous rocks followed the 

 same general line as the older movement admits of little 

 doubt, but that the later structures correspond in detail with 

 the earlier is improbable. 



A brief examination of the region where the Carboniferous 

 rocks disappear under the Secondary formations will give 

 the grounds for this statement. There we find that the 

 Trias passes over the complicated fle.xures of the Mendip 

 axis in undulations so gentle as to prove that those flexures 



