ROCKS OF SHROPSHIRE, 661 
C. Eymwrencr FoR PRECAMBRIAN AGE. 
1. Stratigraphical. 
It will be sufficient to collect a few of the facts detailed in the 
previous sections. 
On the 8.E. side of the Wrekin the proof is very clear. The axial 
rocks, striking W.S.W., are overlain by quartzites striking to the 
S.W. The quartzites are succeeded by the Hollybush Sandstone, and 
the Hollybush Sandstone by the Shineton Shales (Tremadoc). The 
Hollybush must thus be of, at least, Upper Cambrian age; the 
quartzites must be of, at least, Lower Cambrian age (they are proba- 
bly Precambrian), and the volcanic series must be Precambrian. 
The discordance between the axial and the flanking rocks will be 
still more evident when the dips are compared. ‘The volcanic series 
dips N.N.W., while the quartzites dip 8.K. <A greater unconformity 
could hardly be imagined. These relations are expressed in figs, 
2, 3, and 5. 
In Caer Caradoc the sections are still more satisfactory. Un- 
doubted Lower Cambrian rocks, the Longmynd series, are brought 
down against the N.W. side of the axis, the discordance of strike 
between the two formations approaching a right angle, the Pre- 
cambrian beds dipping northerly, the Longmynd slates westerly (see 
fig. 7). ‘These Lower Cambrian rocks probably hold the same rela- 
tion to the axis on its N.W. side as far to the N.E. as Wrockwar- 
dine, or even to Lilleshall, being masked by a thin covering of Car- 
boniferous strata at the N.W. base of the Lawley, and by Triassic 
deposits in the Wellington district. 
The Wrekin and Caer Caradoc chain is the axis of a great anti- 
clinal. The formations dip away on both sides, and their dip is de- 
termined by the upheaval of the Precambrian nucleus. But the 
axial rocks themselves do not share in the anticlinal arrangement, 
being wedges of stratified rock thrust up, after consolidation, between 
parallel faults. This peculiar method of mountain formation is 
paralleled in the Malvern chain and in the Dimetians of St. Davids, 
J have elsewhere * described this structure as ‘“ plagioclinal.” 
2. From included fragments. 
In the middle of the Longmynd series of Haughmond Hill, near 
Shrewsbury, is a great bed of conglomeratey, coloured ‘ green- 
stone” on the Survey Map. It commences a hundred yards or so 
E. of the Castle, and runs in an unbroken line for more than a mile 
to the N.N.E. Its superior hardness gives it in some places a some- 
what mural appearance. It is made up of rounded pebbles cemented 
in an ashy-looking matrix. Amongst the pebbles I recognize a grey 
* Geol. Mag., May 1879. 
+ [have already used this argument in the ‘ Popular Science Review,’ January 
1879, 
