W. G. Fearnsides—Lower Ordovician Rocks of Scandinavia. 301 
known outcrop. The less altered Upper Black Shales of Malvern? 
and the Upper Oldbury Shales of Stockingford* are even more 
Scandinavian in aspect. 
The Lower Tremadoc Slates* or Viobe beds,* on the other hand, have 
nothing in common with any Scandinavian rock 1 have seen. They 
occupy the stratigraphical position of the Acerocare zone of that area, 
but are not known to contain any of the fossils characteristic of that 
zone. As discussed in my Arenig paper,’ the change of lithology at 
their base is very abrupt, and in the absence of other evidence may, 
I think, have brought the new Asaphidian fauna into power in 
Britain before the corresponding displacement of Olenids took place 
in Scandinavia. It was for this reason that I sought so carefully and 
laid so much stress upon the discovery of the Asaphidian genera 
Niobe, Symphysurus, and Megalaspis within the middle and upper parts 
of the Acerocare zone of Sandby, Jerrestadt, and Krekling, and I claim 
that the existence of these genera at such a horizon puts the strati- 
graphical correlation of the MWiobe beds of Britain with the Acerocare 
zone of Scandinavia upon a firm paleontological basis. 
The Obolus bed mentioned in my discussion of the Shineton Beds of 
Penmorfa*® and there grouped with the Lower Tremadoc is very like 
the Odolus sandstone at the base of the Dictyonema shales of Oster- 
gdtland, and is better considered as the basal member of the British 
Dictyonema shales. 
The Dictyonema shales of Wales have a lithology which is unlike 
any of the Scandinavian Dictyonema rocks. The Tremadoe Dietyonema ® 
in the Cambridge Sedgwick Museum collection, like my own from 
Arenig and Dolgelly, have their cells very badly preserved, but on the 
whole are Dictyonema rather than Dictyograptus. Their characteristic 
grouping in radiating colonies of four or six individuals is not well 
seen in any of the Scandinavian museum specimens, but is strongly 
suggested in the ill-preserved examples from the lowest Dictyonema 
beds of Krekling and Sandby, and I am of opinion that the Welsh 
Dictyonema sociale represents a very low horizon within the Dictyonema 
series. The Mary Dingle (Shropshire) specimens seem to be of 
D. flabelliforme type, while the Pedwardine and Bronsil shale 
specimens of Malvern include both low and high types. The Merivale 
specimens, so far as I know them, are indeterminate. 
Of other graptolites we may probably consider the Clonograptus or 
Bryograptus of Shineton as equivalent to the lower Ceratopyge shales 
of Norway and Clonograptus and D. norvegicus beds of Fagelsang, but 
of the position of the Barf slabs’ with Bryograptus I do not feel so 
certain. 
The main fossiliferous horizon of British Tremadoe rocks, which 
includes beds just above and just below the Tai Herion Flags of 
1 Croom: Q.J.G.S., 1902, p. 39. 
2 Lapworth, ‘‘ Geology of Birmingham District’’ : Proc. Geol. Assoc., 1898, p. 337. 
5 Ramsay, ‘‘ Geology of North Wales’’: Geol. Surv. Memoir, vol. iii. 
4 Fearnsides: Q.J.G.S., 1905. 
> Rep. Brit. Assoc., 1902, p. 614. 
6 D. sociale, Salter: Appendix to Ramsay’s ‘‘ Geology of North Wales”’ (Geol. 
Surv. Memoir), vol. iii, p. 331. 
7 Marr: Geox. Mae., 1894, p. 122. 
