THE STEUCTUEE OF THE GULLY, DUEDHAM DOWNS. 69 
horizontal shelf of oolite. Indeed, judging by the lower 
surface of calcite rock, (5), this shelf must even vise to the 
south. The surface of the fault would have to be like that 
of an extremely deep spoon. Again, all the evidence in the 
Gully is of yielding due to pressure, not to relaxation, i.e. of 
a tendency to thrusting, not to normal faulting. On the 
whole, one is driven to the conclusion that too many improba- 
bilities are involved in such an hypothesis. 
Two facts then came to light. One was that the great 
thrust exposed in the old quarry at the foot of the Gully, and 
again on the southern hillside, described above as (a), points 
exactly towards the problematical series. Secondly, that the 
texture of the limestone in the vertical series corresponds 
exactly to the band in the Middle Limestone Shales described 
as C, or to non-rubbly parts of -£J. 
I have no doubt that the true explanation is as follows. 
Horizontal compression took place after the Carboniferous 
Limestone had been lifted up into an anticline. Yielding, as 
indicated by the vertical thrust, took place in a plane passing 
through the locality in question ; and by it a dint or notch 
was produced in the dipping upper surface of the Gully Oolite, 
into which the immediately succeeding bands of the Middle 
Limestone Shale were forced. Such a notch would, of course, 
present a lower horizontal shelf or floor, a vertical back wall, 
and two more or less vertical sides. Such is exactly the 
shape of the notch in the Gully Oolite into which the shaly 
series has been let. Moreover the oolite behind the notch would 
be much crushed, and consequently softer. The depression in 
it, as described in the account of the contour of the Gully, 
accords well with this. Again, the shales would snap at the 
lip of the horizontal shelf, and get driven to the back of it, 
so that although originally dipping at 26° thej^ would now 
become vertical. 
Everything I have yet discovered fits in exactly with this 
