40 GEOLOGY OF SHROPSHIRE. 
two narrow gorges. The south-westerly, and by far the largest, mass is 
the Wrekin proper, and is 12 miles in length. The north-easterly hill, 
called the Ercal, is of less height than the Wrekin and of about half 
the length. The central hump, Lawrence Hill, is still lower, and 
occupies about a quarter of a mile of the length of the range. The 
quartzites rest against the volcanic axis in a nearly continuous band, 
striking to the south-west, parallel to the axis, broken by the above- 
named ravines, and apparently disappearing towards the summit of the 
chain. They reappear, however, towards the south-west end, and lap 
round the south-westerly spur of the mountain. I have taken numerous 
dips on the flanks of the Ercal, Lawrence Hill, and the Wrekin, and 
find that the direction of dip is on the average a little to the east of 
south-east, and its amount about 45°, ranging between 30° and 55°. 
Other exposures on the flanks of the range are scanty. Judging by the 
shape of the ground and soil indications, the quartzite is probably con- 
tinuous all round the Wrekin range, with the possible exception of the 
two points under the summit, one on each side. 
The thickness of the quartzite, measured at the. north-east end of 
the Ercal and at Lawrence Hill, is about 200 feet. 
Lying to the west of the Wrekin, and connected with the quartz 
rocks just described by a narrow isthmus, is an irregular area of quartzite, 
three miles in length from north-east to south-west, and 14 miles in its 
greatest breadth. Through these strata are thrust up four bosses of 
bedded volcanic rock, the largest of which is Charlton Hill, with two 
small masses immediately to the south, and a larger exposure a mile to 
the south-west. The dips of these quartzites are very varied. In the 
road one-third of a mile south of the spot marked ‘“‘ Charlton, Mill” on 
the Ordnance map, they are displayed in a good section dipping south- 
easterly at 60°, and resting immediately upon igneous rocks. ‘Two or 
three hundred yards to the north-east is quartz rock resting on porphyry 
of the Charlton Hill boss, and dipping to the south at 45°. One-third of 
a mile to the south of this last spot is another exposure of quartzite, 
dipping away to the south from the more southerly of the two small 
volcanic masses. A mile to the east-north-east of Charlton Hill, at the 
village of Rushton, quartz rock strikes north and south at a high dip; 
and a little to the north-west of Rushton the dip is westerly. One-third 
of a mile east of Rushton, in the quarry marked with an arrow on the 
map of the Geological Survey, the quartzite dips to the south at 30°. 
These dips are too irregular to be referred to any one upheaving force. 
Wherever the quartz rock occurs in close proximity to igneous rocks it 
dips away from them; and it seems not improbable that other dips at a 
distance from exposed volcanic masses may be caused by local upheavals 
of volcanic rock which do not appear at the surface. 
(b.) Caer Caradoc sub-area—The quartzite reappears eight miles to 
the south-west of the last area, on the south-easterly flank of Caer 
Caradoc, near Church Stretton, an igneous hill of similar character to 
some of the Wrekin rocks, and evidently belonging to the same series. 
It is also less distinctly exposed at the south-west end of the south-east 
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