LATERAL PRESSURE IN THE BRISTOL DISTRICT. 149 
The folding of the Palaeozoic rocks in the Bristol district is 
of a comparatively gentle type as compared with that which 
results from the acute stress in a typical mountain region. It 
is true that the Carboniferous strata in some parts of the 
district have been thrown into a nearly vertical position, and 
that near Rowberrow, on Mendip, there is some evidence of 
fan-structure. Still, I am not aware that any estimate has 
been formed, or that there are sufficient data on which such 
an estimate could be based, as to the thickening or thinning 
of the strata under lateral pressure. Without going so far 
as to admit that this mode of effecting a diminution of hori- 
zontal extent in the Bristol area is strictly speaking a negligible 
quantity, it must be confessed that this cannot be introduced 
into any calculation based on actual measurement. 
The effects of dislocation and faulting can in certain cases 
be expressed in quantitative terms. But it is not easy fairly 
to distribute these effects over the whole area. The Chfton 
fault has caused an overthrust of nearly 1,000 yards, or 
certainly more than half a mile, measured horizontally. 
Faults between the Chfton-Clevedon ridge near Clapton-in- 
Gordano on the one hand, and Portishead on the other, have 
brought about lateral displacement through two and a half 
miles as a maximum, while another fault of unknown extent 
has thrust coal measures over mountain hmestone on the 
foreshore at Portishead. Further north, at Cattybrook, there 
is evidence of another large fault probably of the reversed 
type. An extensive fault presumably hes in the space which 
intervenes between the Middle Hope hmestone ridge of Wood- 
spring and that of Worle Hill. And within the Coal-measures 
of the Radstock district Mr. McMurtrie has described an over- 
lap fault with a maximum displacement of 330 yards in a 
horizontal direction. These are only some of the faults in 
our district. Though the average amount of diminution of 
originally horizontal extent throughout the area does not. admit 
of any reliable quantitative estimate, still it is clear that this 
