PROCEEDINGS OF GEOLOGICAL SOCIETIES, 
4G3 
*' On the Wigan 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 Up-Holland, present a lofty range of hills, and divide the 
Wigan from the St. Helen's coal-field. 'W ith, 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 sandiitoues 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 LTp-Holland 
Stations, llesting 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 
under clay. 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 thieknet^s of thirty-three feet, are either impure or too tliin 
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. Tbe 
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 Gannel Coals, of each of which this field furnishes 
an ample and excellent su])ply. As a rule, the scams 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 diff erences 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 
rohusta, 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- 
