22 
POPULAR SCIENCE REVIEW. 
strata of Haughmond Hill, near Shrewsbury, the 64 busky hill ” 
of Shakspere’s Henry IV. is a great bed of conglomerate, 
coloured “ greenstone ” on the map of the Geological Survey. 
The pebbles of which this rock is mainly composed are of reddish 
felstone, resembling some of the Wrekin felstones. This con- 
glomerate was certainly derived from land of a similar mineral 
structure to the Wrekin, and it is only six miles distant from 
that elevation ; but it would be somewhat rash to assume that the 
Wrekin was the only mass from which the felstone pebbles could 
have been derived. There is, however, no doubt that Pre-Cam- 
brian land existed in Lower Cambrian times somewhere in the 
neighbourhood of the Wrekin. 
Emerging from the dimness of these ancient epochs, we come 
into the clearer light of the Silurian period. The dawn of that 
age shone upon the Wrekin rising sharp and lofty above the 
waves. During the Arenig and Llandeilo periods, the forces of 
the atmosphere were incessantly employed in reducing its size 
and rounding its outlines. In a south-westerly direction, its 
base, consisting of a framework of Upper Cambrian shales, ex- 
tended several miles. Towards the Caradoc epoch, the Wrekin 
island began to sink, and was lapped round by Lower Caradoc 
sandstones and conglomerates. The depression still went on, 
successive strata of the Caradoc formation overlapping each 
other on to the sloping Cambrian margin. In the Lower Llando- 
very period the motion was reversed, and no strata were deposited 
round the island ; but in Upper Llandovery times depression 
was resumed, and was continued till the Pentamerus Limestone 
and its associated conglomerate margined the very flanks of the 
Wrekin itself, and the succeeding deposits of the Wenlock and 
Ludlow periods probably surrounded and buried the greater part 
or the whole of the mountain. 
During the period of the Old Red Sandstone, the Wrekin rose 
again above the ocean, while the forces of the sea and air were 
actively at work in stripping off the superincumbent layers of 
Upper Silurian rock, and once more exposing the buried moun- 
tain to the light of day. 
Early in the Carboniferous epoch, depression once more 
commenced, and sandstones were deposited round the lower 
slopes of the Wrekin, succeeded by coral-reefs and banks of 
shells. Then the surrounding sea gradually shallowed, gave 
place to low swampy land covered with ferns, lycopods, and 
sigillariae, and inhabited by insects. These land surfaces, by 
oscillations of the crust, alternated with clays containing marine 
shells and king-crabs. 
The later part of this period was marked by active vulcanism. 
Numerous volcanic cones were dotted over the West-Midland 
counties. The Rowley Hills, near Dudley, and the Clee Hills, in 
