GEOLOGY The basin-like area of this coalfield causes the mines lying above the Arley to have a much diminished superficial area, so much so that Professor Hull calculated that the Mountain Four-Feet Mine, which passes under the whole of the Middle Measures, may yet be made to yield 100,000,000 tons, or more than the whole of the seams of the Middle Series. , UPPER COAL MEASURES These measures are better developed in the Manchester area than in any other part of Englaiid. The development is, however, altogether local, the other areas of Upper Coal Measures in Lancashire being of insignificant proportions. A small patch of shales and flaggy sandstones in the Wigan area, overlying a coal supposed to be the Worsley Four-Feet, belongs probably to the lower part of the Upper Series. Another small patch occupies the southern border of the South Lancashire Coalfield in the neighbourhood of Leigh, Worsley, and Pendleton. A portion of the same measures forms a similar border to the Middle Series from Kingley to Prestwich, but has been carried to the north by the great Irwell Valley Fault. The Upper Coal Measures along the southern border are partially concealed by the overlap of Permian and Trias. Since they are mainly unproductive, they have not been exploited. They consist of reddish shales, clays, and sandstones with thin bands of limestone and a calcareous hasmatite, worked at Patricroft. They also contain a coal known as the Yard Coal of Pendleton. MANCHESTER COALFIELD This small coalfield has already been mentioned as one in which the Middle Coal Measures are still untouched, the rocks nearest the surface belonging solely to the upper series. Considerable light has been thrown upon these by the construction of a new line of railway along the eastern outskirts of Manchester in 1890-91. The succession of beds belonging to the Upper Coal Measures was exposed, as well as their junction with the Permian. Full details of the sections are to be found in papers of C. Roeder, C. E. De Ranee and J. W. Brockbank.i The series as a whole consists of reddish mottled clays, shales, and sandstones, with thin bands of limestone. At Ardwick, near the centre of the coalfield, and in the railway section to the south, twelve beds of limestone are shown, the total thickness in the former case being 29 feet, in the latter 21 feet 4 inches. The general dip is southwest, the lowest members of the series cropping in the north-east of the district, and being succeeded regularly by others until the thin limestones of the upper part come in along the southwest border. Below the lowest limestone are about 200 yards of strata under which the following section was obtained at the Bradford Colliery : — ^ Bradford and Clayton Coal Series Ft. In. Ft. In. Openshaw Mine 3 o Four Feet Mine .... 3 10 Strata about 135 o Strata 108 o Charlotte Mine 20 Yard Mine .... J to i o Strata 210 o Strata 210 o Three Quarter Mine ... 17 Two Feet Coal 20 Strata i5 O Strata 120 o Coal o 10 The total thickness will not fall far short of 2,000 feet. All the seams have now been worked out, but twenty years ago several collieries were busily engaged. It must not be supposed however that the coalfield is exhausted, for underneath the 2,000 feet of Upper Measures is a rich Middle Series similar to that of Oldham, Ashton-under-Lyne, and Dukinfield, and it is very probable that this will eventually be sought for and mined. Should this ever be the case, and the Middle Coal Measures be reached, another 80 feet of coal, spread over nearly 4 square miles, will be added to the coal resources of Lancashire. 1 Trans. Manch. Geol. Soc, xxi (i 890-1-2), and Pm. Lit. and Phil. Soc, Manchester, for same year. 2 ' Geology of Country around Oldham, including Manchester and its suburbs,' Mem. Geol. Survey (1864), p. 35. 19
