HUGHES : INGLEBOROUGH. 
355 
There is a cross system of folds running generally N.N.E. 
and S.S.W., and the intensity of the disturbance increases as 
we pass across these from east to west, and also as we traverse 
the various folds from north to south. The upturn on the 
south rim of the London basin is much more gradual than that 
seen in the Isle of Wight, and the folds of the South Wales Coal 
Field are less severe than those found along either the Bristol 
Channel anticline or among the Coal Measures of Somerset, and 
far less intejise than those seen among tlie crushed and plicated 
rocks of Devonshire. These general inferences from observations 
made over wide areas teach us what we should look out for in 
examining the details of any similarly folded rocks within the 
region affected by such movements. One leading fact estab- 
lished by these inquiries is that through Central Wales, across 
the Midlands and East Anglia to the sea, there was an ancient 
line of movement which affected the distribution of the Bala 
and Silurian in Wales, brought Carboniferous and older beds up 
through the Secondary rocks in the Midlands, and threw the 
Tertiary beds far out to sea in East Anglia. 
We find that towards the close of the epoch represented 
by the Bala Beds there followed conditions under which sediment 
free from volcanic material was everywhere spread over the 
lavas and ashes which form the greater part of that series in 
North Wales and the Lake District. 
Now volcanic outbursts are not the cause, but the conse- 
quence, of earth movements, but they may be always regarded 
as indicating such movements. Therefore we have reason to 
believe that over the region north of the Mid- Wales uplift the con- 
ditions were different not only in respect of the rapidity, extent, 
and exact age of the earth movements, but also, over consider- 
able areas, in respect of the material of which the sediment was 
composed. South of the great central uplift the Bala Beds are 
composed chiefly of mud ; while north of it they are made up 
largely of volcanic material. South of it the Silurian consists 
of mudstones with important intercalated limestones, which 
extend over very wide areas considering their small thickness, 
while north of it the sediment was coarser and has given rise 
to immense formations of flags and sandstones. The change in 
