August i8, 1904] 



NA TURE 



385 



been found to possess the structure of a broken monocline, 

 a fold with fracture such as may be regarded as an early 

 stage in the formation of an ovcrthrust from the east. Jt 

 runs through the coalfield in a direction slightly east of 

 south, and then passing under the Trias of Stafford ranges 

 for Wolverhampton ancl Stourbridge. This fault is mainly 

 pre-Triassic, but what Mr. Gibson believes to be a con- 

 tinuation of it, following the same direction as far south 

 as Hanbury, certainly effects a great movement in the 

 Trias. 



The third disturbance runs on the east of the Korest of 

 Wyre Coalfield in a direction a little west of south. Here, 

 as I learn from Mr. '1". C. Cantrill, the thrust from the east 

 is obvious, for Old Red Sandstone has been pushed from 

 that direction against and even over Coal Measures, while 

 the strata have been forced up into a vertical position for 

 some miles. In South Staffordshire all the Carboniferous 

 rocks, including the "Salopian Permian," are involved in 

 Ihis and the previously mentioned movement, proving ihnt 

 both disturbances were of post-Carboniferous date. 



Traced southwards this disturbed belt leads to Abberley, 

 and there connects itself with the well-known Malvernian 

 axis. The broken belt known by that name runs north 

 .-ind south, and may he followed almost continuously from 

 Worcestershire to Hrislol. It presents evidence of having 

 been a line of weakness through a large part of the world's 

 history, as shown by I'rof. Groom, and of having yielded 

 repeatedly to earth-stresses; but there is seldom dilVicully 

 in distinguishing the movements which were effected 

 during the period under consideration. I'or example, near 

 and south of .Abberley the Coal Measures are clearly in- 

 volved in a thrust from the east, which was sutlicienlly 

 energetic to turn over a gfeat belt of Old Red .Sandstone 

 and other rocks beyond verlicality for some miles. Further 

 south, again, among repeated proofs of the ridging up of 

 the old axis in several pre-Carboniferous periods, we find 

 evidence of post-Carboniferous elevation along the same 

 general line. Throughout this same region there has been 

 also post-Triassic dislocation, which, however, is on a com- 

 paratively small scale. That the Carboniferous rocks were 

 greatly disturbed before the Trias was laid down is proved 

 by the great unconformity between the two formations. 



The Malvernian axis continues southwards by Newent, 

 but perhaps with diminishing intensity. On its west side 

 a broad syncline rolls in the tract of Carboniferous rocks 

 which underlies the Forest of Dean. The syncline trends 

 north and south, and is shown to be of pre-Triassic age 

 by the fact that the Triassic strata on the banks of the 

 Severn do not share in the synclinal structure. Here ue 

 must leave the Malvernian axis for the present. 



The fourth disturbance ranges along the I.ickey Hills, 

 which, diminutive as they are, tell a slory of great geo- 

 logical significance. They range in a south-south-easterly 

 direction, and in the fact that they are formed of extremely 

 ancient rocks furnish evidence of immense upheaval. From 

 the relations of these ancient formations to one another we 

 may gather also that the upheaval was due to a recurrence 

 of movement along the same axis at more than one 

 geological date, but at the same time we find no difliculty 

 in distinguishing that part of the movement which took 

 place between Carboniferous and Triassic times, for the 

 Coal Measures are tilted up on end along the flanks of the 

 axi-, while the Trias passes horizontally over all the tilted 

 rocks. \ clue to the southward extension of the axis under 

 the Secondary rocks is furnished by some faulting as far 

 as Redditch, here also there having been a renewal of 

 Tiiovement on a small scale in post-Triassic times. 



The fifth disturbance runs through Warwickshire, and 

 includes the low ridge of ancient rocks which ranges 

 through .\therstone and Nuneaton in a south-easterly direc- 

 tion. .About fifteen miles to the north-east .Archai^an rocks 

 form the parallel ridge or series of ridges of Charnwood 

 Forest, while the intervening space is overspread by Trias, 

 resting partly on Carboniferous and partly on older strata. 

 The structure of the Carboniferous and older strata is 

 dtjminated by what is known as the Charnian movement, 

 which includes disturbances of .several ,-iges ranging in a 

 south-easterly direction. That part of the movement which 

 was post-Carboniferous is identifiable by the fact that Coal 

 Measures are tilted on either side of the ridges of old 

 rocks. Thev once overspread both ridges, but were 



NO. 1816, VOL. 70] 



removed by denudation as a consecjuence of upheaval before 

 the Trias was deposited. It has been found also in working 

 the coal, as I am informed by Mr. Strangways, that there 

 are large faults having the south-eastward or Charnian 

 direction which shift the Coal Measures, but do not break 

 through the overlying Trias. The evidence, therefore, of 

 a great Charnian movement having taken place during the 

 period under consideration is conclusive. The disturbance 

 ranges as a whole in the direction of Northampton, where 

 in fact borings have reached the Charnwood rocks at no 

 great depth. 



The five great disturbances which I have briefly indicated 

 tend to converge northwards, but their exact connection 

 with the Pennine axis is not known. What may be only 

 a part of that axis trends for Charnwood through a tract 

 of Lower Carboniferous rocks exposed at Melbourne, 

 between the Yorkshire and Leicestershire Coalfields, but 

 Ihe Triassic channel I have ;dready mentioned intervenes, 

 and the structure of the rocks underlying the red marl is 

 unknown. The channel itself appears to be of Triassic 

 age, for not only is the depth of marl in it suggestive of 

 its having been a strait in the Triassic waters, but its 

 northern margin has been found by Mr. Gibson to coincide 

 with, and perhaps to have been determined by, faults 

 known to be mainly of pre-Triassic age. One of these, 

 with a downthrow of 400 yards to the south, runs from 

 Trentham through Longton, and south of Cheadle, while 

 another ranges from near Nottingham to the north of 

 Derby. 



We come now to the south-west of ICngland, where we 

 find striking proofs of a still more energetic movement 

 than any yet mentioned having intervened between the 

 Carboniferous and Triassic periods. The central part of 

 the .Armorican axis, as it has been called, after the ancient 

 name of Brittany, trends nearly east and west, and keeps 

 to the south of our South Coast ; but we have opportunities 

 in Devon and Cornwall of seeing some of the stupendous 

 effects produced along its northern side. A belt of country 

 measuring some 130 miles in width has been completely 

 buckled up. Slaty cleavage was superimposed upon the 

 intricate folds into which the strata were being thrown, 

 while after or towards the close of these phenomena 

 granite was extruded at several points along the belt of 

 disturbance, a little north, however, of the line along 

 which the oldest rocks were brought up lo the surface. In 

 Devon the Culm-measures are fully involved in the move- 

 ment, but on the other hand the Permian strata, while 

 containing fragments of the cleaved and metamorphosed 

 rocks, are themselves wholly free from such structures. 

 The age of the folding, cleavage, and extrusion of the 

 granite is thus definitely fixed as having been subsequent 

 to the deposition of the Culm-measures, but previous to 

 that of the Permian rocks. 



But we may fix the age still more closely. A broad 

 .syncline of Carboniferous rocks traverses Mid-Devon, and 

 is succeeded northwards by an anticline and by an extru- 

 sion of granite at Lundy Island, the age of which, how- 

 ever, has not yet been definitely ascertained. Still further 

 north in a series of folds and overthrusts which traverse 

 the southern margin of .South Wales we can recognise the 

 last effects of the great Devonshire movement at a distance 

 of not less than 130 miles from the central axis, the 

 ground-swell, so to speak, subsidinir as it receded from 

 the distant storm-area. Here the higher Carboniferous 

 rocks are involved, and thus prove that this oart at least 

 of the .\rmorican disturbance was of post-Carboniferous 

 age. 



In Dorset, Somerset, and Gloucestershire the Pakeozoic 

 rocks pass eastwards under Secondary formations, and are 

 seen no more in the south of England. That the disturbance 

 continues, however, is inferred from the fact that it has 

 been traced across a large part of the continent of Europe 

 in the one direction and across the south of Ireland in the 

 other. The determination of its position therefore, and 

 especially of the effects of its intersection with the Midland 

 disturbances, is of the greatest importance in view of the 

 possible occurrence of concealed coalfields under the 

 Secondary rocks. One such intersection is open to observa- 

 tion. 



The Malvern and Devonshire disturbances intersect in 

 .Somerset. On investigating their behaviour as they 



