GEOLOGY OF SHROPSHIRE. 43 
least on the outside of it with regard to the axis of elevation. This is 
well seen in the Wrekin sub-area, and stillmore distinctly on the south- 
east flank of Caer Caradoc. 
But the age of the Hollybush Sandstone must first be determined. 
It is commonly placed upon the horizon of the Ffestiniog group, on the 
ground that it underlies the Black Olenus Shales of Malvern, which are 
with great probability correlated with the Dolgelly series. But the 
relations of the Hollybush and Black Shales are very obscure, and it has 
not been shown that they succeed each other conformably. The late Mr. Belt 
considered the Hollybush to be a shore deposit of the Menevian sea; but 
I am willing to accept the former determination till decisive evidence is 
forthcoming. The quartzite, then, is older than the Ffestiniog period. 
But the Hollybush sandstone and the quartzite do not succeed each other 
conformably. In the Wrekin areathedipsare so discordantas to suggest a 
considerable gap. The quartzite, in most cases, dips away from volcanic 
bosses, and the direction of dip is determined by these local upheavals. 
But the dips of the Hollybush are subject to no such law. Their general 
direction on the south-east of the Wrekin, where the quartzite dips 
south-easterly, is to the south-west; but in one place they appear to 
conform to the dip of the quartzite, and at a little distance they plunge 
at a high angle to the north-west (that is, towards the quartzite.) South 
of Charlton Hill, also, the sandstone dips towards the quartzite. The 
apparent conformability of the two formations at Caer Caradoc cannot 
counteract such clear evidence of discordance. Parallelism of strike does 
not prove conformity, since a strike fault might let down the upper of 
the formations without producing any alteration in the dip or strike. 
It is clear, therefore, that the quartzite is older than the Hollybush 
Sandstone by a gap, and consequently cannot belong to any part of the 
Upper Cambrian series. 
Three hypotheses now remain. The quartzite may be on the 
horizon of the top of the Lower Cambrian; or it may belong to the 
Lower Cambrian; or it may be Precambrian. 
(a.) The top of the Lower Cambrian (Longmynd Series.)—The Lower 
Cambrian of Shropshire, as is well known, is a great series consisting of 
fine-grained slates or hardened shales in the lower part, and of sandstones 
and conglomerates above. For reasons which I cannot here detail, I 
believe that neither the base nor the top of the succession is seen, being 
cut out by faults. Does the quartzite represent a lost capping of the 
Longmynd rocks? I think the great discordance between the quartz rock 
and the Hollybush Sandstone decisively negatives this supposition. 
(b.) The Longmynd Series—No band of quartzite has been observed 
in this series from top to bottom. If the quartz rock represents any 
part of the Longmynd succession, where are the beds which on this 
supposition should intervene between the quartzite and the Precambrian 
voleanic series? Or is the quartzite a basement of the Longmynd 
rocks? If so, there should surely be some concordance of dip and 
strike. But the Longmynd strata in their lower part almost uniformly 
dip at very high angles to the west-north-west, whereas the quartzite, 
