116 
term Dudley limestone, except as the synonym of Wenlock, with which he pro¬ 
ceeds to show its lithological and geological identity. This limestone is described 
in detail at the Castle Hill, Wren’s Nest, and Hurst Hill, in all of which it forms 
ellipsoidal elevated masses, 500 to 650 feet high, protruding through the coal 
measures in lines parallel to similarly shaped masses of Ludlow rock at Sedgeley, 
&c.; i. e ., tending from 10° E. of N., to 10° W. of S. Two strong bands of 
limestone occur in these hills, overlaid and separated from each other by shale, 
charged with numerous small concretions of impure limestone, the “ bavin” of the 
workmen. The limestone having been quarried out from these bands, wdiich have 
been raised up from a common centre, and disposed with a quaquaversal dip at 
high angles, it is evident that the hills themselves would ere now have been demo¬ 
lished, had they been composed throughout of calcareous masses of equal purity; 
but the “ bavin” or refuse composes the framework of these perforated hills, and 
preserves their outline. The Wenlock shale, or underlying part of the formation, 
constitutes the nucleus of the Wren’s Nest, the largest and most perfect of these 
ellipsoids, and of this the author gives a detailed plan. These ellipsoids usually 
feather off at one extremity with a broken-down margin, and thus complete their 
resemblance in physical features to ancient craters of eruption.* The greatest 
superficial extent of the Wenlock formation is in the neighbourhood of Walsall, 
where it rises both in dome-shaped masses and in rectilinear ridges, running from 
S.S.W. to N.N.E., parallel to the axis of the Wolverhampton coal-field, of which 
one of these ridges forms the eastern boundary, the limestone plunging beneath 
the coal-field at a rapid angle. The other ridge is continuous with the new red 
sandstone of the Bar-beacon, and is known as the Hey Head lime. In the Dud¬ 
ley, or ten-yard coal tract, few works have yet proceeded downwards beneath the 
lower coals, and hence the subjacent Silurian rocks are little known to the miners. 
A remarkable and accidental discovery of a mass of limestone took place recently, 
near Dudley Port, on the rise side of a great fault, which bounds the downcast of 
the coal, called “ Dudley Trough.” Having worked out the coal on the upcast 
side, a shaft was sunk in and upon the southern side of this fault, when, at a depth 
of 208 yards, and about 100 yards below the exhausted coal strata, a mass of lime¬ 
stone was met with, which proved to be near seven yards thick, and of very good 
crystalline quality. Being found to extend in a form more or less horizontal, ex¬ 
tensive works were promptly opened in it for the extraction of a rock so precious 
in the heart of the coal-field. When the author visited it, a considerable cavity 
had been formed, in which no trace of moisture was discernible, whilst it was 
known that copious streams of water were flowing in the coal measures overhead. 
He accounts for this mass of limestone being hermetically excluded from the per- 
* See account of Valley of Woolhope for similar phenomena on a larger scale, and with 
a greater number of concentric and enveloping formations .—Proceedings Geol. Soc., vol. id., 
p. 15. 
