Chap. VI.] WENLOCK FOSSILS. 119 
In the exterior of the nucleus, which also consists of shale, the calca- 
reous matter disappears ; but the limestone itself is quite similar, in com- 
position and colour and in its large hailstones as well as small concre- 
tions, to the rock at Wenlock. 
At Woolhope in Herefordshire (see p. 110, and woodcut) a similar uprise 
from the centre has produced, as we have seen, a much grander phenome- 
non. In the Silurian region the Wenlock formation has seldom a greater 
thickness than 1000 feet ; but in Wales, though void of limestone, it occa- 
sionally assumes more than double those dimensions. 
The most prominent fossils of the limestone, among which Corals abound, 
have long been known to collectors, who have derived their chief supplies 
from Dudley and its environs. Those persons who are searching for "Wen- 
lock fossils may, however, be told that their labour will probably be better 
rewarded by a visit to the northern end of the Wenlock Edge, near Coal- 
brook Dale, than to Dudley ; for the Corals, Encrinites, and Shells along 
this rich escarpment are easily detached from the matrix, and the quarries 
Fossils (18). Corals &c. of the Wenlock Limestone. 
1. Favosites cristatus, Blum. 2. F. Gotlandicus, Linn. 3. A variety of this Coral ; 
and 3*, 3**, magnified portions of two varieties. 4. Favosites asper, d' Orb. 5. Alve- 
olites Labechii, Milne-Edw. 6. Ceriopora oculata, Goldf. ? 7. Favosites fibrosus, 
Goldf. 8. A variety incrusting Shells. 
have not yet been exhausted. Benthall Edge, for example, which over- 
hangs the Severn in so picturesque a form, and Gliddon Hill are excellent 
localities f. This rock is indeed distinguishable from all the inferior strata 
by the very great abundance of its Corals, the profusion of which makes 
it resemble in many places a coral-reef. These Corals were admirably 
described for me in the original * Silurian System ' by my valued friend 
Mr. Lonsdale, who made the first eifort to classify them and to compare 
them with the determinations of continental naturalists. 
t Some of the finest Corals originally published in the • Silurian System. ' were collected by the Rev. 
T. T. Lewis, in the gorge of the Raver Lugg, above Aymestry. 
