LATERAL PRESSURE IN THE BRISTOL DISTRICT. 151 
north and the neighbourhood of Shepton Mallet to the south, 
a distance of thirty miles, the percentage of reduction due to 
lateral pressure is in round numbers 2 '5 per cent, or 132 feet 
in the mile. In a section at right angles to this axis drawn 
through Bristol, and in length twelve miles, the reduction is 
3*5 per cent, or 185 feet in the mile. 
It may be noted that the Bristol district Ues in a region in 
some degree transitional between the predominantly north 
and south anticHnes and syncHnes of northern England, with 
the Pennine axis as a sahent physical feature, and the predomi- 
nantly east and west antichnes of the south, of which the 
Mendip axis is an expression. The effects of lateral pressure, 
with a grip from east to west, are more marked in the northern 
part of the Bristol district ; those of pressure exerted from 
north and south are more marked in the southern part of the 
district. Hence the somewhat triangular form of the Glouces- 
ter and Somerset coalfields regarded as a whole. 
Taking all the facts of the district into consideration, and 
making allowance for the effects of faulting, it appears that a 
mean reduction of original area by 3 per cent., or in round 
numbers 100 feet in the mile, may be taken as a reasonable 
estimate of the quantitative effects of lateral pressure as 
exerted on the Carboniferous rocks in Pre-mesozoic times in 
this part of England. 
The suggestion I would offer is that similar estimates should 
be made for other parts of England, so that we may, by cor- 
relating the results, reach some conception of the total amount 
of compression which the rocks of the British Isles have under- 
gone in the successive periods in which they have been sub- 
jected to the stress of lateral pressure. 
