W. G. Fearnsides—Lower Ordovician Rocks of Scandinavia. 297 
C. The Didymograptus Shales and Orthocerkatk. 
Coming now to deposits which all are agreed to place within the 
Ordovician system, I can add but little to what has been already 
published. ‘The graptolitic equivalents of the Arenig or Skiddavian 
groups of England have been ably discussed by Professor Tornquist in 
Sweden! (C) and by Dr. Lapworth and Miss Elles® in this country. 
The present generation of Swedish geologists (S 1) seems agreed in 
calling these by Moberg’s name, the Didymograptusskiffer (85), just 
as it also unites the graptolitic equivalents of Llandeilian and 
Caradocian under Tornquist’s Dicellograptusskiffer. Graptolitic 
deposits are, however, not the only type of Ordovician sediments in 
Scandinavia, and though in Kristiania, Hunneberg, and the greater 
part of Skane the lower half of the Arenig is wholly graptolitic, the 
calcareous deposits of the more eastern provinces must not be forgotten. 
These limestones have long been known as the Orthocerkalk or 
Orthoceras limestone, but until comparatively recently they have only 
been classified by their colour, and the fact that they come in at lower 
and lower horizons as we pass eastward until in Oland they represent 
the whole of the lower as well as the middle and upper Arenig seems 
to have been overlooked. Taking these calcareous deposits first, we 
may note the modern paleontological classification due to Moberg and 
applied by Hedstrom & Wiman (0 1) to the island of Oland— 
Ancistroceraskalk, with a Llandeilo trilobite fauna. 
Centauruskalk, with Jilenus centaurus, Ogygia dilatata, ete., and 
Didymograptus geminus. 
Platyuruskalk, with Asaphus platyurus, Echinospherites, Lituites, 
and many trilobites. 
Gigaskalk, with Wegalaspis gigas. 
Upper Asaphuskalk, with a rich but undescribed fauna of small 
trilobites, Orthoceras tolerably common. 
The Spheronite Bed, built up of Spheronites pomum. 
Lower Asaphuskalk, with an exceeding rich fauna, including some 
24 species of trilobites and a Phyllograptus. 
_ Limbatenkalk, with many Iegalaspis limbata, Endoceras, Orthoceras, 
Gasteropods, etc. 
Planilimbatenkalk, with Megalaspis planilimbata, Niobe, Symphysurus, 
and several other genera common to the Ceratopygekalk, into 
which it passes. 
The corresponding classification of the graptolitic deposits due to 
Tornquist (G) and applied by Térnebohm & Hennig (S1) to the 
rocks of Skane is— 
Upper Didymograptus shales : 
(6) Zone of Didymograptus geminus, in which Diprionidian 
graptolites become abundant ; 
(a) Zone of Phyllograptus cf. typus, in which Diprionidian © 
graptolites are very rare ; 
1 *“ Nagra anmarkningar om vestra Europas Kambriska och Siluriska Korologi”’ : 
G.F.F.S., 1889, p. 299. 
2G. L. Elles: ‘The Graptolites Fauna of the Skiddaw Slates’’ (Q.J.G.S., 
1898, p. 463); ‘‘Some Graptolite Zones in the Arenig Rocks of Wales,’ 1904, 
Graptolites, parts 1 and 2 (Pal. Soc.). 
