612 MR. F. A. STEART ON OVERTHRUSIS AND OTHER [ Nov. 1902, 
been entirely shorn off: as, for example, in the case of the Middle 
Vein (see fig. 1, p. 610). When the workings reached the com- 
mencement of the overthrust, it was found that the coal-seam 
dipped slightly towards it ; and after continuing for some distance to 
dip in this manner, it began to thicken from an average of 2 feet to 
6 or 8 feet. It then began to rise rapidly, until it became per- 
pendicular and finally inverted, so that the floor of the seam now 
formed the roof, and the hard sandstone-roof formed the floor. This 
was found to continue, until the seam and associated strata gradually 
again became vertical, and ultimately regained their former state 
with the soft black shale under foot and the hard sandstone overhead. 
The workings have not been sufficiently extensive to give the 
dimensions of these overthrusts in each seam, but they are greater 
than those of the overthrust on the north side. The continuity of 
the coal-seams throughout the overfold has been practically proved 
in the cases of the Great Vein, Top Little Vein, and Middle Vein. 
As the overthrusts, however, appear to increase uninterruptedly 
in magnitude below this point, it is very probable that these more 
deeply-seated seams have been entirely shorn off, and are not 
continuous. 
It is a matter of interest whether, in the case of the great over- 
thrust at Radstock, the amount of overlap still continues to increase 
in the same manner below the Bull Vein, as above that seam. 
If this should be so, the amount of overthrust in the coal-seams 
of the Farrington Series, some 200 yards below, would be very great. 
If, however, the Radstock overthrust is a magnified reproduction 
of the smaller braysdown thrusts to the north of it, then it seems 
probable that this will not be the case, for the following reason. 
The overthrust on the north side of Braysdown Colliery has been 
proved in the Farrington Series, where, however, it occurs on the 
south side of the pit. This overthrust, as before mentioned, has 
been traced in all the Upper or Radstock seams. It was met with 
in the shatt, where it probably accounted for the unusual thickness 
of Red Shales; and on the south side of the shaft, in the working of 
the first seam of the Farrington Series, the dimensions of this over- 
thrust (or the linear extent of the displacement) have been found 
to be practically the same’ as that on the Bull Vein or last seam 
of the Radstock Series, and therefore the fault (or vertical distance 
by which the same coal-bed has been separated) may not be larger, 
nor the overthrust (or extent to which the ends overlap) be any 
greater below this point. 
If we accept the theory that these Braysdown faults owe their origin 
to the same cause as the Radstock overlap-fault, it is reasonable 
to suppose that when the Radstock Fault is proved in the Farrington 
Series, it will be found to have the same dimensions approximately 
as in the bottom seam, or Bull Vein, of the Upper Series. [If this 
be so, proof will be afforded that these faults did not take place 
until after the last-named seam had been deposited. 
1 In some cases slightly less. 
