20 
POPULAR SCIENCE REVIEW. 
Previous to this elevation, or perhaps subsequently, the sand- 
stone was converted into quartzite. 
On its north-west side, the Wrekin, with its overlying quartz 
rocks, is bounded by a fault separating it from the Bunter sand- 
stone, the lowermost division of the Triassic rocks of North 
Shropshire. But on the south-east the quartzite is succeeded 
by green sandstones, formerly supposed to be of Caradoc age, 
which the writer has demonstrated to be the true Hollybush 
Sandstone of the Malvern Hills.* Not only does this rock con- 
tain two common Malvern fossils, Kutorgina cingulata and 
Serpulites fistula ; but it is precisely similar to the Malvern 
sandstone in lithological and mineral characters. Outside of 
this band of Hollybush Sandstone is a parallel zone of shales, 
which have been shown in the same paper f to be of Tremadoc 
age. The quartzite, the Hollybush Sandstone, and the Tremadoc 
Shales are separated from each other by faults, and, from the 
structure of the whole country, it is clear that they were 
successively deposited at distant intervals. The Tremadoc Shales 
are Upper Cambrian; the Hollybush Sandstones are probably 
Lower Cambrian ; and the quartzite has been shown by the 
writer if to be Pre-Cambrian. 
It was intimated early in this paper that some part of the 
Wrekin rose above the waves in one of the Pre-Cambrian epochs. 
In the lower part of the quartzite, on the south-east side of the 
mountain, small pebbles of decomposed felstone, showing the 
characteristic banding of some of the Wrekin rocks, are im- 
bedded. Besides this, the quartzite is wanting under the sum- 
mit of the hill on both sides, so that the summit was probably 
dry land during the deposition of the sandstone. These facts 
seem to point to the following sequence of events. The Pre- 
Cambrian sandstone (now quartzite) was deposited round an 
island of felspathic rocks, the partial denudation of which sup- 
plied the pebbles. Subsequently, the wedge-like upthrust pre- 
viously described took place, and a north-east and south-west 
ridge of felspathic rock, set in a framework of sandstone or 
quartzite, rose above the waves of the Lower-Palaeozoic Sea. 
That rocks of the Wrekin chain formed dry land in times 
preceding the Cambrian will be further evident from the follow- 
ing considerations. In a low elevation, about two miles west of 
the Wrekin, is a good exposure of Pre-Cambrian rocks with their 
usual east and west strike. These ancient strata here contain a 
band of well-marked conglomerate, consisting of rounded pebbles 
of quartz, mica-schist, pink felstone, and an imperfect granite. 
* tl Quart. Journ. Geol. Soc.” vol. xxxiii. p. 662. 
t Ibid. pp. 657-662. 
f Ibid. vol. xxxiv. p. 754. 
