Chap. VI.] 
WENLOCK SHALE. 
113 
shells are mixed with others essentially Wenlock. After lucidly explain- 
ing how such transitions harmonize with well-understood operations in 
nature, and that in this locality there is no firm and hard boundary be- 
tween the inferior and superior strata, Professor Phillips thus writes : — 
" As a general result, it is quite evident that the successive changes of or- 
ganic forms, as they are exhibited to us in the successive groups of strata, 
are not simply dependent on the lapse of time, nor explicable as a series 
developed in proportion to the time, unless we survey the phenomena over 
very wide areas, and include in the comparative terms geological periods 
long enough to neutralize the influence of peculiar physical conditions. 
These," he truly says, " on account of their local origin, limited area of 
effect, and recurrence at indifferent periods, have at almost every geogra- 
phical point, at some epoch or other, broken or mingled the series of or- 
ganic life " *. This is and has long been my belief, as founded on exten- 
sive observation. 
A limestone subordinate to shale, and bearing precisely the same relations to 
a subjacent sandstone as that of the localities above cited, occurs on the western 
and south-eastern flank of the Lower Lickey Hills in Worcestershire. There 
the Silurian rocks consist of Pentamerus sandstone, overlapped on its edge by 
shale, in which are courses of limestone (at Colmer's End), the whole having 
been thrust up as an irregular dome through the overlying coal-measures and 
red sandstone. Again, in the adjacent tract near Walsall, and between that town 
and the Barr Beacon, the same" Lower Wenlock or Woolhope limestone, long 
worked at the Hay Head, dips away from a point of similar sandstonef, to pass 
at a gentle angle of 8° or 10° under the great body of the shale with its cal- 
careous nodules and numerous small fossils, the whole being covered by the 
thick or chief limestone exhibited in the great quarries of Walsall. The rock 
contains nearly all the fossils found at Woolhope, and notably Bumastus 
Barriensis, Foss. 17, p. Ill, named from the adjacent village, and called by fossil- 
collectors the ' Barr Trilobite,' together with many forms common to the whole 
formation, including Orthocerata and Corals J. 
In this way proofs have been obtained that a limestone the real place 
of which was indicated in several detached districts as being inferior to the 
great mass of shale, is by its fossils the lowest calcareous member of the 
Wenlock formation. 
Wenlock Shale. — The shale, which is infinitely the largest and most 
persistent member of the Wenlock formation, occurs both below and above 
the Woolhope or lower limestone, — the latter being absent in many tracts, 
and in others represented solely by a few small elliptical and round con- 
cretions of impure and earthy limestone. The pure shale is well exposed 
* See Memoirs of the Geological Survey of of the sediments and other conditions of the 
Great Britain, vol. ii. p. 75. This line of thought habitats of the marine animals now fossilized, 
is admirably carried out by Dr. Bigsby in nis t Mr. Jukes indicated to the Geological Society 
memoirs on the Silurian rocks and fossils of the the existence of this point of sandstone. See also 
State of New York, Wales, &c, Quart. Journ. Geol. his excellent detailed Survey of this district, Ee- 
Soc. Lond. vols. xiv. & xv., where he works out the cords of the School of Mines, vol. i. pt. 2. p. 240. 
statistics of genera and species as to their succes- He i3 now preparing a third edition of this me- 
sion, recurrence, and extinction, and of the dis- moir. 
tribution in connexion with the mineral characters J See Sil. Syst. p, 488* 
I 
