THE STRUCTUEE OF THE GULLY, DURDHAM DOWKS. 65 
running to the north-east across the Downs, corresponding 
to each of the Heads of the Gully. 
The Gully shows excellently what is elsewhere displayed 
in the Avon Gorge, that the lateral pressure from the 
south, which produced the Great Clifton Fault, also left its 
mark on the whole mass of Carboniferous Limestone dis- 
played in the Gorge. As in the Great Quarry, the faults in 
the Gully are of a very peculiar type. They are not normal 
faults, neither are they in the usual sense of the word 
thrust-planes. What has happened is that vertical or 
highly inclined cracks have appeared, and one side, usually 
the western, has been pushed along on these almost 
horizontally, or with a very slight rise. They differ then 
from ordinary thrust-planes in that the fault-surface is 
nearly vertical instead of being nearly horizontal. I shall 
therefore refer to them as vertical thrust-planes. They 
were probably produced either at the time of or just before 
the Great Fault. 
With this introduction we may proceed to examine the 
exposures in detail. 
(a.) A well marked thrust-plane is twice exposed, once in 
the old quarry at the bottom of the Gully, and again in the 
Gully Oolite on the southern slope above this quarry. The 
thrust-surface slopes to the north-west at an angle of about 
80° ; the direction of the plane (and of the movement) is 
35° E. of N. It is marked by slickensides rising at an 
angle of about 5° to the north-east. It cuts the whole face 
of the cliff in the quarry, maintaining precisely the same 
direction in the exposure on the slopes above the quarry. 
It was the rocks on the western side of this vertical 
thrust plane that were pushed past the others, probably only 
a few yards. 
There is some evidence of faulting in the northern corner 
of the quarry. 
F 
