C. EH. de Rance—Sections around Southport. 503 
The following table gives the general thickness :— 
Below the Arley Mine. 
Bittner District. Horwicu District. 
Heet oa Feet in. 
lack Shales i501) cs) saa ke 210 Sandy Flagstones so) Sos l0 
Lower Coal-measures (Upholland 
os 
Flags and Shales)... 850 0 Lower Coal-measures... 852 0 
Upper Mountain Mine’.. 2 0 = 4) ards MGC ee ace 1 4 
Fire Clay and Shales see eee LOMO 
Fire Clay Coal baie 10 Measures: +) 2th See Lea) 
phalesyand Bullion: 250.05. .05, 245) +0 
Bullion Coal ... ane 8 = Upper Foot Mine. 
Shales and Flags goo) doog Boo) eon I IMCASUIKES aun piece) ieosuo ONO, 
Gainister’ Coat i... ces Ms 2 = Gannister Coal. 
aVRCASURCSHMNen yh exes fesse ecaks aes OST NS IMfeasures: 22.89 oh Sos Oo GenO 
PED GH CORI  Wisae) Vice: | Wade 1 33 =Lower Foot Mine ... 136 
CAS URES Mh Pepe; haces! leSei a. waay Uioe VO, 
Lower Mountain Mine ... 2 S| S950 Micasutes, ) UGay eas ea OOOO 
Lower Coal-measures... ... ... 836 4 
hough Roce... i. rs 100 ough: Rocks). 62.) 1 200m 
Between the Middle Coal-measure-black shale at Bury and the 
underlying Lower Coal-measure-flagstones occurs a physical break. 
There is little doubt that the Middle Coal-measures are everywhere 
unconformable, but it is difficult to make out the relation. 
The Lancashire Coal-basin, by faulting and subsequent denudation, 
has become separated into four distinct districts; the largest and 
most important of them is the Wigan and Bolton field; to the north- 
east is the Burnley Coal-field; to the south-east is the Manchester 
Coal-field, which at present is confined to working Coals in the 
Upper Coal-Measures. 
I have found it convenient to divide the Middle Coal-measures 
of the Wigan area into the following groups, for the purpose of 
comparing them with the adjacent areas, as follows, in descending 
order :— . 
Groups. From To the 
F. Tue Ince. the Ince Yard Coal. Pemberton, 5 feet. 
EK. Tor PemMBerton. the Pemberton, 5 feet. Wigan, 5 feet. 
D. Tue Wiean. W. 5 feet. Wigan 9 feet. 
C. Tur Cannet-Kina. W. 9 teet. Yard Coal. 
B. Tue Bone. Yard Coal. Orrell 5 feet coal. 
A. THE ORRELL. Orrell 5 feet. Orrell 5 feet, or Arley 
Mine. 
Following these groups from Prescot to Wigan, the vertical 
thickness between the Arley mine and the Ince Yard mine is found 
to increase from 1400 feet to 2200 ft., the measure having thickened 
50 feet per mile, for each of the 16 miles traversed, the rate of in- 
crease of the first 4 miles being at the rate of 82 feet per mile, the 
average being reduced by the last 6 miles increasing only at a rate 
of 20 feet per mile. On the eastern margin at Burnley, in which 
the attenuation of the thickness of the measures from the centre of 
the basin is still more marked, the vertical thickness here being 
1 The word ‘‘ Mine” is used in parts of Lancashire, instead of ‘‘ Coal,’’ for certain 
seams. 
