444, SECTIONAL TRANSACTIONS.—C. 
The Coal Measures in this area are covered by 
(3) Bunter Sandstones ; 
(2) Permian Marls with Limestones ; 
(1) Collyhurst (? Permian) Sandstones. 
The Collyhurst Sandstones are mainly confined to the area around Man- 
chester and Stockport, and their rapid and irregular variation in thickness 
(from 0 to 1,500 feet) within that area is only intelligible on the supposition 
that they are separated from the overlying Permian Marls by a strong un- 
conformity. They appear to be separated from the Coal Measures below by 
a further unconformity. There is no definite evidence in this area of uncon- 
formity between the Bunter and the Permian Marls. 
The Lancashire Coalfield occupies the N.E. angle of the rhomb-shaped 
‘ Cheshire basin,’ which may be regarded as bounded by the Ribble anticlines 
(N.E.-S.W.) on the north-west, the Audley anticline (N.E.-S.W.) on the south- 
east, the Pennine elevation on the east, and the Clwydian elevation on the 
west. The basin was probably subdivided in pre-Triassic by an E.-W. elevation 
passing a little south of Macclesfield and Chester, while the northern part of the 
basin is further subdivided by the Rossendale anticline (E.-W.), cutting off the 
Burnley basin, with the Knowsley anticline (N.E.-S.W.), which continues it 
to the south-west. A minor anticline of the N.E.-S.W. series modified the 
eastern side of the basin near Stockport. 
The Lancashire Coalfield is probably separatcd from the Flint Coalfield by 
the N.-S. anticline which passes near Prescot, and which is probably con- 
tinued under the Triassic cover to the south. 
The partial basin with the limits just defined has a diameter of about 
thirty miles, and an area about three times that of the exposed coalfield. 
This basin is further modified by two very pronounced troughs, due princi- 
pally to faulting, which cross the exposed coalfield—the Irwell Valley trough 
and the Wigan trough. Both trend N.W.-S.E., and within each there is minor 
folding, which appears to be related to the faulting. In each case the depth 
of the trough increases towards the margin of the basin. A third trough 
between St. Helens and Prescot has exactly the same characters, except that 
its boundary faults trend N.-S. 
The detailed study of the faulting of this area fully substantiates the recogni- 
tion of two main groups N.W.-S.E. and E.-W. The former series includes all 
the largest faults. A third series trending nearly N.-S. is almost restricted 
to the eastern and western sides of the basin. While these directions are on 
the whole clear and distinct, and the dominance of the N.W.-S.E. series is very 
pronounced, there appears also some tendency to a convergence of these latter 
faults towards a point on the buried extension of the Ribble anticline about 
five miles south-west of Preston, suggesting a possible torsional strain. 
The great majority of the faults are very regular planes, cases of apparent 
irregularity being due as a rule to combination of several faults. In the 
middle of the coalfield are several very instructive cases where displacement 
has attempted to follow a line midway between the N.W.-S.E. and the E.-W. 
fractures; the result being a zigzag fault following first one direction, then the 
other. Only one notable case of a fault following a curved course (turning 
through some 80°) has been met, the Bickershaw Lane fault. 
The faulting is on a larger scale than in any other British coalfield. The 
1,000 yards fault (Irwell Valley) is famous. There are seven or eight with 
throws exceeding 500 yards, and as many again nearly approaching that figure. 
One fault mapped may have a displacement of 1,500 yards or more. 
The hade of the faults can be demonstrated only in a minority of cases. 
It is very variable in large and small faults alike. Several of the largest 
have a hade of 45° or more, while others are nearly vertical. The average hade 
is probably not far from 30°. Most of the E.-W. faults appear to be very 
steep, but with that exception there is no apparent relation between the trend 
or direction of throw and the hade. 
A rough estimate of the lateral expansion of the area necessary to allow 
for the formation of the faults met with between the east and west ends of 
the coalfield gives a minimum increase of 21 miles in a present length of 
