302 W. G. Fearnsides—Lower Ordovician Rocks of Scandinavia. 
Arenig,' the Belswardine locality at Shineton,? and the Pen Morfa 
Post Office beds? near Tremadoc, has much in common with the 
highest Ceratopygeskiffer of Kristiania. The fact that they also yield 
Dikellocephalus, Cheirurus, and Ampyx-like forms, however, also 
connects them with the true Ceratopygekalk, and on the whole we 
may say that they belong to the horizon where Shumardia is most 
abundant. 
Of the Upper Tremadoc Slates* with Angelina, which are known 
only about the Tremadoe estuary, I can say little, except that, like the 
Wiobe beds below, they are totally unlike any Scandinavian. series 
I have seen. As, however, in Wales they overlie the Shumardia 
horizon and have a considerable thickness we must conclude that the 
too represent some part either of the upper Ceratopygekalk or of the 
basal portion of the Planilimbatenkalk, but, if so, difference of lithology 
must account for a very great difference in fauna. 
The Ogygia marginata and Peltura punctata beds of Caermarthen- 
shire ® I am unable to correlate, but would suggest that the Ogygia is 
probably a Megalaspis and is not. very like any known Tremadoe or 
Ceratopygekalk form. The Nesewretus beds of Dr. Hicks® also have 
more in common with the Lower Asaphuskalk of Eastern Sweden 
than with any older bed. 
The unconformity which separates Tremadoc from Arenig rocks in 
North Wales corresponds to some extent to the break which 
separates Dictyonema or Ceratopyge shales from the Glauconitic beds 
and Ceratopygekalk in Eastern and Central Sweden, but occurs, 
I think, at a higher horizon. 
Of reputed Arenig rocks the graptolitic beds have been compared 
in detail by Miss Elles’ with the Didymograptus shales, and it will 
here suffice to mention that among these Skiddaw Slates we have the 
only known British equivalents of the zone of Zetragraptus phyllo- 
graptoides and a possible continuous passage up from the Tremadoc. 
In Wales the lowest Arenig horizon is not lower than the upper part 
of the zone of Didymograptus balticus, and in North Wales probably 
comes within the Phyllograptus cf. densus zone. The upward succession 
above this is continuous, and can be checked zone by zone by means 
of its graptolitic bands. The trilobite beds, like those of the Tremadoe, 
are not so comparable, and their ashy constitution seems to have had 
great effect upon the faunas which have little in common with those of 
the trilobitic Orthoceras limestone. The Erwent Limestone ® of Arenig 
and the WVeseuretus beds of South Wales® have, however, a general 
aspect not unlike the Asaphuskalk of Oland. 
For more general comparisons I will refer readers to parts 1 and 11 
of the new monograph of the Swedish Ceratopyge region by Moberg 
1 Fearnsides: Q.J.G.S., 1905. 
2 Callaway: Q.J.G.S., 1877, p. 652. 
3 Fearnsides: Rep. Brit. Assoc., 1902, p. 614. 
* Ramsay, ‘‘ Geology of North Wales” (Geol. Surv. Memoirs), vol. iii. 
5 Crossfield & Skeat: Q.J.G. S., vol. lii (1896), p. 5238. 
6 Hicks: Q.J.G.S., p. 39, vol. ‘xxix, 
7 Elles: Guou. Mas., 1904. 
8 Fearnsides: Q.J.G.S., 1905. 
® Hicks: Q.J.G.S., vol. xxix, p. 39. 
