TRANSACTIONS OF THE SECTIONS. 83 
tent than the cross faults which run respectively S.E. and S.W.; and 
they also form, in many instances, the terminations of the cross faults, 
being rarely, if ever, crossed by them. The average ‘throw’ of the 
_ principal or northerly faults is about 340 yards, whilst that of the 
cross faults is only about 44 yards. Beginning at the easterly side 
of the map, which comprises about 50 square miles of the district, 
_and proceeding to the westward, the 
1st principal fault throws down the strata to westward . 171 yards 
- 2nd do. do. do. about 500 do. 
8rd do. throws up do. do. 340 do. 
4th do. throws down do. do. 440 do. 
5th do. throws up do. do. 540 do. 
and the sixth throws the strata up to the westward about 220 yards, — 
_ the average distance between them being about 1200 yards. The 
level and dip of the coal vary in each belt of strata respectively in- 
cluded between the main faults. Between the two most easterly of 
them the dip is nearly south, whilst between the second and third it is 
west, or at right angles to the former. The plan shows the variations 
of the dip and level in each belt of strata, the directions of which are 
indicated by blue lines. The lines of the subsidiary or cross faults 
generally form angles of from 30 to 60 degrees with the main fault, 
and searcely ever form right angles. The fault, or plane of dislocation, 
is rarely, if ever, found to be vertical, but deviates generally from that 
position from 20 to 40 degrees. It is also invariably found that the 
inclination of the plane of dislocation indicates the direction in which 
_ the strata are displaced. If, for instance, the vein of the fault slopes, 
forming an inclined plane, the foot of which is nearer the observer 
than the summit, the strata are in that case removed upwards; if, on 
the contrary, the plane of dislocation slopes from the observer, the 
strata are removed downwards, as shown by the Section. In all the 
seams of coal subjacent to the district comprised in Mr. Peace’s map, 
the direction of the cleavage of the coal strata in every seam is inva~ 
-riably N.W., and varies but a very few degrees; and in this important 
characteristic they correspond with many observations the author has 
- made in the coal districts of Yorkshire, South Wales, and elsewhere, 
which induce him to believe that it is an effect of one and the same 
_ cause acting simultaneously on the whole of our coal strata during 
_ their deposition. 
3 On that part of the South Welsh Coal Basin which lies between the Vale 
of Neath and Carmarthen Bay. In explanation of a geological map 
of the district, laid down by the author on the sheets of the Ordnance 
Survey. By Mr. Locan. 
The map exhibited the outcrops of the various seams of coal in the 
district in question, and the dislocations they suffer from faults. 
_ All the principal faults run in a north and south direction, and pre- 
sent an extraordinary degree of parallelism. 
They coincide with the joints of the rocks, and it is very usual 
G2 
