146 OBSERVATIONS ON THE 
What we learn from a comparison of this horizon in Sections 
A and B is that the great series of May Hill Sandstones, so 
largely developed at Llandovery as to have suggested changing 
the old name from May Hill Sandstone to Llandovery Rocks, 
is greatly diminished in thickness as it approaches the Malvern 
pre-Silurian ridge and becomes more variable, as indeed might 
be expected in basement beds. 
A strong conglomerate made up of the underlying rocks and 
full of characteristic fossils marks the actual base. The blocks 
of syenite are so welded on to what was probably originally a 
calcareous matrix that it is difficult sometimes to see the exact 
line of demarcation, and some interesting reactions not yet 
explained, but well-worth attention, have taken place between 
the calcareous sandy mudstone and the felspathic syenitic— 
pegmatitic or gneissic rock. 
SEecTIon C. 
We will now cross over some 150 miles or so, and examine 
the Silurian’ Rocks where they come out in Westmorland and 
Yorkshire from beneath the Carboniferous and newer rocks of 
the Counties of Flint, Chester, and Lancaster. 
At the top of the Silurian Rocks here we find no passage 
upwards into any overlying series. The basement beds of the 
Carboniferous Kocks lie transgressively across the edges of all 
the Silurian Rocks, and rest in places on the Bala or Arenig 
Series below, as may be seen for miles along the grand 
precipices of Ingleborough, in the river sections of the Rawthey, 
near Sedbergh, in the valleys of the Birkbeck and Lune, near 
Tebay, and in fact all round the Cumbrian pre-Carboniferous 
island. At the base of the Carboniferous there are irregular 
pockety patches of red and variegated shales, limestones, 
sandstones, and conglomerates, which may represent the 
extreme edge of the Devonian Rocks thinning out on the shore 
of the gradually submerged pre-Carboniferous land. For land 
there undoubtedly was over all this area between the deposit of 
the Silurian and of the Carboniferous Rocks. I measured the 
edges of the sedimentary rocks which had been cut off before 
the land went down again, and found that subaerial and marine 
coast denudation went on to such an extent in that interval that 
some 27,000 feet of sedimentary rock had been removed in the 
interval, and this was arrived at by estimating only the thickness 
of the beds and not the folds, and without taking account of 
any possible extension of the Merthynian over this area. This 
is, perhaps, the greatest unconformity which can be measured 
in all the geological series, and yet only a short distance to the 
south the base of the upper series or Devonian has so thickened 
and so much of the beds that succeed the Silurian conformably 
have been preserved, that it might be and has been doubted 
whether any break should be drawn through what has 
erroneously been bracketed together as the Old Red of South 
Wales and Hereford. 
