464 
TUE GEOLOGIST. 
cashire T\liereYer they occur. A series of great " faults," or dislocations, 
running almost parallel with each other in a X.N.W. direction, and nearly- 
equidistant, divide the coal-field of Wigan into a succession of belts. Minor 
faults branch away from the main faults in all directions, and break up the 
strata into numerous subdivisions. Moreover, each fault and branch fault 
has a certain and considerable inclination to one side or another in its 
course, varying from one to three vertical to one horizontal. Hence every 
locality requires to be " proved," either by boring or by the sections of ad- 
jacent collieries, so that in sinking a shaft the miner may avoid faults, and 
"win," at the least outlay, the greater number of seams of coal. The forces 
which occasioned the dislocations have diminished in power northwards, 
and the extent of their ''upthrows" and '* downthrows " vary over the 
field in question from a few yards to upwards of six hundred. The effect 
of great upthrows has been the loss of many valuable seams in some loca- 
lities, and that of downthrows to preserve them, while their combined re- 
sult has been in one part of the field or another to cause every seam to 
have one or more " outcrops." The courses of these " outcrops " are clearly 
traced on the recently-coloured maps of the Geological Survey, and some 
of the most favourable situations for viewing them, as well as sections of 
the district, are given in the memoirs of that survey, by Mr. Hull. The 
coal-bed roofs of the lower measures of Wigan include remains of drifted 
plants and Sigillariae, and, in the under-clays, Stigmaria. The " floors," 
or under-clays of the coal-beds of the middle measure abound with Stig- 
marise, or the roots of Sigillariae, the stems of which occasionally intersect 
a coal-bed, but are generally found in the roof. Especially is this the case 
in the roof of the Four Feet Ince Mine, where, from their upright position 
and ponderous weight, and the nature of the roof itself, they are the fre- 
quent cause of melancholy accidents. The coal-beds themselves are vast de- 
positories of fossil vegetation, the forms and tissues of which are for the most 
part obliterated ; but in the roofs are found, beside Sigillariae, numerous 
Ferns, Asterophylites, Calamites, Lepidodendrons, and Coniferse. The 
fauna of the Lower Coal-measures of Wigan furnish Anthracosia, Modiola, 
Gonudites Listeri, and AvicuJo-pecten papyraceus. In the roof of the 
Lower "Mountain Mine " is a fish-bed containing bands, full of Cypris or 
Cythere, Microconchus carhonarius, Anthracosia, and more rarely Gonia- 
tites, fish-bones, scales, teeth, etc. The middle series QOTdmn Anthracosia 
rohiista in abundance, and the varied remains of two fish-beds, one over 
the Arley and the other over the Cannel mine. From Mr. Hull's memoirs 
we learn also that the late Mr. Peace, mining-agent to the Earl of Bal- 
carres, collected from the latter bed beautiful specimens of fish, of the 
genera Megalichthys, Holoptychius, Diplopteris, Ctenoptychius, and some 
large dorsal rays. Some idea of the immense value of this coal-field may 
be deduced from Mr. Hunt's Mineral Statistics for 1861. He gives the 
total quantitA'- of coals raised that year in the United Kingdom as 83,635,214 
tons, of which 12,195,500 tons were raised in Lancashire. The number of 
collieries (not pits) then in Lancashire was 375, the proportion in the 
Wigan district being 78. An uniform average quautitj^ for each colliery 
would show the produce of the Wigan coal-field that year to be about 
3,000,000 tons. Eight shillings per ton at the pit's mouth, — a low enough 
estimate for Cannel and all sorts, — would give £1,200.000 as the produce of 
the mines for one year. The facilities at some of the Wigan collieries for 
executing extensive orders for shipment in a very short time are surprising. 
.At Rose Bridge Colliery, for instance, the property of Messrs. Case and 
Morris, Mr. Bryham, the able and obliging manager, states they can raise 
with ease a thousand tons per day, or fifteen hundred tons in the twenty- 
four hours, by working night and day. 
