PROCEEDINGS OP GEOLOGICAL SOCIETIES. 



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"On theWigan Coalfield." By Mr. S. B. Jackson. — The area treated 

 of was illustrated by Farrimond's valuable mining map and list of strata. 

 These served also to indicate the multitudinous " faults " and dislocations 

 of the district, and the " outcrops " of the numerous seams of coal by 

 which it is enriched. The Wigan coal-field contains the lower and middle 

 series of the Lancashire coal-measures. The former are thrown up at 

 Billinge and Tip-Holland, present a lofty range of hills, and divide the 

 Wigan from the St. Helen's coal-field. With this exception, the superficial 

 aspect of the region is undulating, and presents no remarkable natural 

 feature. The Millstone Grit constitutes the lowest known rock in the dis- 

 trict, and the portion exposed at Grimshaw Delf is about 100 feet thick ; 

 resting upon it are the lower coal-measures, 1800 feet in thickness. They 

 consist of a series of micaceous flags, shales, and thin beds of coal, with 

 their floors of underclay, containing Gannister, a peculiarly hard siliceous 

 stone, which, in the first instance, gave the name of " Gannister beds " 

 to the series in which it is found. They contain six seams of coal, de- 

 signated " Mountain Mines," having an aggregate thickness of about nine 

 feet. Only two of the seams have been found worth working, and those 

 to a limited extent. The sandstones of this series are even-bedded, show- 

 ing ripple-marks and sun-cracks, and are very extensively used for flagging 

 and roofing-purposes, splitting along planes, formed of micaceous flakes. 

 A good section of the lower measures may be seen in the cutting of the 

 Lancashire and Yorkshire Railway between Pimbo Lane and Up-Holland 

 Stations. Resting upon the micaceous flagstones, just referred to, is the 

 base of the middle coal-measures, which attain a thickness of about 2400 

 feet. They consist of an alternating series of reddish-grey and yellow 

 sandstone, shales of various character, and beds of coal, with their 

 underclay. This series is the most prolific of coal, containing not less 

 than forty-five seams, with an aggregate thickness of 100 feet. Two- 

 thirds of the number of seams, ranging from two to thirty-two inches, 

 with a total thickness of thirty-three feet, are either impure or too thin 

 to pay for working. The remaining fifteen seams contain about sixty- 

 seven feet of coal, and are those which are exclusively worked in the 

 Wigan coal-field. These range from about two to ten feet in thickness. The 

 properties and qualities of the respective seams of coal differ considerably, 

 as do also remote and detached areas of the same seam. Generally speak- 

 ing, the whole may be grouped into three classes, viz. the Free-burning, 

 the Bituminous, and the Cannel Coals, of each of which this field furnishes 

 an ample and excellent supply. As a rule, the seams which exceed four 

 feet in thickness are inferior in value to those which are four feet or under, 

 and in most cases the quality near the outcrop is not so good as in the 

 deep. The most valuable seam in this series is the Cannel Coal, and next 

 to it the Orrell Four Feet, or Arley Mine, which at Wigan closely re- 

 sembles the famous Wallsend of the Newcastle field. This seam being the 

 lowest, is sometimes worked at a great depth. At the centre of the Wigan 

 basin (say under Wallgate), it is about 863 yards from the surface. Our 

 limits preclude a particular description of the several seams. Notwith- 

 standing differences of thickness in strata, and of the quality of the vari- 

 ous seams of coal in the two districts, there exist such analogies between the 

 coal-beds of Wigan and those of St. Helen's that miners entertain no doubt 

 of their identity. Indeed, the prevalence of a thick bed of Anthracosia 

 robusta, commonly called the " Cockle-shell Bed," occurring upon a sub- 

 stratum of under clay, about sixty feet above the Arley mine, taken in con- 

 junction with the nearness of the Gannister beds below, enables the geolo- 

 gist to identify the strata at the base of the Middle Coal-measures of Lan- 



