Parr II.-Sxor. ii-§2.] SILURIAN. ° 677 
dying out, to reappear again perhaps some miles away with increased 
proportions. This local character is well exhibited by the Woolhope 
‘limestone. Where it disappears, the shales underneath and intercalated 
with it join on continuously to the overlying Wenlock shale, and no line 
for the Woolhope sub-group can then be satisfactorily drawn. ‘The 
same discontinuity is strikingly traceable in the Wenlock limestone, to 
be immediately referred to. 
(c.) Wenlock Shale-—This is a series of grey aud black fine shales, 
traceable from the banks of the Severn near Coalbrook Dale across 
Radnorshire to near Carmarthen—a distance of about 90 miles. The 
=> 
Ss 3 S 
BSS 

Fig. 327.—Upprr SILurIAN CoRALS AND CRUSTACEANS. 
a, Acervularia ananas (Linn.); b, Ptychophyllum patellatum (Schloth.) (4); ce, Omphyma 
turbinatum (Linn.) (1); d, Petraia bina (Lons.); e, Ceratiocaris papilio (Salt.); f, 
Homalonotus delphinocephalus (Green) (4); g, Cyphaspis megalops (McCoy) ; h, 
Phacops Downingiz (Murch.). 
same strata reappear in the protrusions of Upper Silurian rocks which rise 
out of the Old Red Sandstone plains of Gloucestershire, Herefordshire, 
and Monmouthshire. In the Malvern Hills they were estimated by 
Professor Phillips to reach a thickness of 640 feet, but towards the north 
they thicken out to 1000 or even 1400 feet. On the whole the fossils 
are identical with those of the overlying limestone. The corals, 
however, so abundant in that rock, are here comparatively rare. ‘I'he 
brachiopods (of the genera Leptsena, Orthis, Strophomena, Atrypa, and 
Rhynchonella) are generally of small size—Orthis biloba, O. hybrida, and 
the large flat O. rustica being characteristic. Of the higher mollusca 
