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The close relationship between the dyke and this fault isobvious ; 
evidence of the nature of that relationship is abundantly 
furnished in the colliery workings of Vobster, Newbury, 
Mackintosh, and Edford, and the numerous workings of less 
importance which have been abandoned. These are all situated 
in the very throw of the convulsions, the results of its action. 
Two ideas suggest themselves as to the nature of their relation- 
ship. First, the escape of the molten material may simply have 
allowed the west side of the fault, the side on which the dyke is 
situated, to rend away from the east side and _ subside. 
If this had been the case, we can scarcely conceive why the 
subsidence should have been confined to one side only. Or, 
else, as the Somersetshire Coal fields are an outlying branch of 
South Wales, from that direction the convulsion might have come 
which brought the Cambrian and Silurian deposits into contact 
with internal heat, resulting in the depression of the basin. 
After the basin had settled down to much the same position it 
is now in on the east side, a second intrusive shock also 
coming from the direction of South Wales may have struck 
the basin, affecting the western side only; causing it to rend 
away from the east side, subside, and further weaken the 
line of fracture of the Mendips, allowing the molten material to 
escape to the surface; that escape or dyke commencing where 
the fault intersects the Mendips. At the moment of eruption, 
the north side of the dyke, being the sinking and consequently 
the weakest, yielded to the tremendous upward and _ lateral 
pressure of the escaping material, was lifted and folded over to 
the north, at the same time thrusting the whole “ country ” north- 
ward in forcing its outlet. The orifice of the dyke at the 
moment of eruption could not have been less than one mile 
wide by three miles long. When the sinking strata of the 
western side of the basin had in due course reached a firm 
foundation and the discharge and consequent upward and lateral, 
pressure removed, the Old Red sandstone and Mountain Limestone 
