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 A HISTORY OF LANCASHIRE POST-CARBONIFEROUS CHANGES The causes which have operated in altering the character of the Lancashire Coal Measures since their deposition are of three kinds, viz. flexures or folding, denudation, and faulting. FORMATION OF SYNCLINES AND ANTICLINES 1. Careful mapping has shown that the whole of the Carboniferous system of Lancashire has been thrown into a number of anticlines and synclines along a line running west of north and east of south, the axes of the folds being north of east and south of west. This folding caused the separation of the Burnley Coalfield from that of South Lancashire, the crest of the intervening arch, ' the Rossendale Anticlinal,' being afterwards denuded down to the Millstone Grit Series. The former field owes its preservation to the formation at this time of the Pendle Hill Range, in which the lower beds are brought up again to the north of the coalfield in a line parallel to the Rossendale anticlinal. The approximate age of this system of folds is indicated by the occurrence of Permian deposits in the Pendle range lying upon the upturned and denuded edges of the Coal Measures, and even overlapping on to the Millstone Grit.^ This evidence shows that the development was post-Carboniferous and pre-Permian, and that denudation of the Coal Measures preceded the deposition of the Permian. 2. The high ground on the east of the Lancashire Coalfield, in which the Millstone Grit Series outcrops, owes its origin to a simple fold formed subsequently to those we have considered, and developed along a north and south line. The fold as a whole gave origin to the Pennine chain of hills now forming the main axis of elevation in the north of England. This huge fold cuts off the Lancashire Coalfield on the west from that of Yorkshire on the east. That the two were formerly continuous is abundantly proved by the close correlation which can be established between them, and the regularity of succession upon each side of the axis of upheaval. The age of this north and south flexure is not by any means clearly determinable. That it was formed before the deposition of the Trias is proved by the latter lying upon the Lower Carboniferous along the southern extremity of the Derbyshire hills,' but that it was post-Permian, as is supposed by Professor Hull, rests upon the belief that a great anticlinal fault traversing Lancashire and contem- poraneous in its development with the upheaval of the Pennine chain is older than a second fault which it meets to the south of Staffordshire. The anticlinal fault fractures the Coal Measures, and passes under the Trias in Staffordshire without fracturing them, but the second fault which it joins fractures both. Immediately to the south of the Lancashire Coalfield the anticlinal fault is accompanied by a parallel series, one of which, known as the ' Red Rock Fault,' throws in the Permian Sandstone against the Carboniferous. If the anticlinal fault and the parallel system above mentioned are of the same age, as seems most probable, it follows that the former, as well as the latter, is of post-Permian age ; and since the anticlinal fault is directly connected with the upheaval of the Pennine Chain, the age of the latter appears to be established as post-Permian and pre-Triassic. It would thus appear that the dominant features of the topoL^raphy of Lancashire were determined by the formation of two systems of folds and the denudation of their crests before the commencement of the Mesozoic. FAULTING 3. The third change which was induced in the Lancashire Coal Measures was caused by the great system of faults which strike across the coalfield from N.N.W. to S.S.E. That these are post-Triassic is shown by their continuance into the Trias of the Cheshire plain. That they are possibly post-Jurassic is assumed, because the continuity of deposition was not interfered with from the top of the Trias to the close of the Jurassic so far as is known. The more important of these faults will be dealt with under their respective districts. Oldham District Several faults start in the neighbourhood of Ashton-under-Lyne and range north-west as far as Rochdale and Heywood, with downthrows of from 100 to 200 yards. Immediately to the east of this district in the Millstone Grit country runs the great Pennine Fault, passing almost north and south, and bringing up the Pendleside (' Yoredale ') shales against the Millstone Grits. 1 Hull ' Observations on the Relative Ages of the Leading Physical Features and Lines of Elevation of the Carboniferous District of Lancashire and Yorbhire,' Quari. Joum. Geol. Soc, xxiv. 323 (1868). 2 Hull, op. cit., p. 329. 20