352 
SILUKIA. 
[Chap. XIV. 
rocks, their lower members, or the Encrinital schists and Orthoceras-limestone, 
characterized by large Orthocerata with central siphuncles, may, however, be 
supposed to represent the Lower Ludlow, — the more so, as they contain Gompho- 
ceras pyriforme. In the overlying shales, Graptolites priodon (Ludensis) abounds ; 
but it is to be noted that this zoophyte is associated with Retiolites Geinitzianus, 
Barr., and Cyathocrinus rugosus, both of Wenlock age, in Britain, — the former 
even pointing to the very base of the formation. 
Even the upper limestones, schists, and shales, as seen at Malmo and the 
places above cited, are still charged with some Corals and Crinoids, known in 
England in the Wenlock formation only, including among the latter Eucalyp- 
tocrinus decorus and Crotalocrinus rugosus. On the other hand, here are also 
found some of the typical species of the Ludlow rocks, viz. Chonetes lata, Rhyn- 
chonella Wilsoni, Rh. navicula, Cyclonema corallii, Pterinea retroflexa, Orthoce- 
ras ibex, &c. 
In my own rapid survey of the environs of Christiania, as formerly explained 
to the Geological Society, I could not, any more than M. Kjerulf, detect fossils 
indicative of the uppermost Ludlow rock, though I then pointed out a conform- 
able passage upwards from the grey Upper Silurian rocks into an overlying red 
sandstone. In some parts of Sweden, however, and on another occasion, my co- 
adjutor M. de Verneuil and myself detected organic remains in strata which 
must, we thought, represent the Upper Ludlow, and even a transition into the 
Devonian. Thus in Scania we found true Upper Ludlow fossils in red flaggy 
sandstones which Forchhammer had classed as Old Red Sandstone *. 
Again, in proceeding from the northern and central parts of Gothland, which 
are occupied by the Wenlock limestone, we at length reached beds of a sandy 
and marly character, in which some of the species above mentioned, including 
Pterinea retroflexa, Chonetes lata, and Cyclonema corallii, were collocated with 
Rhynchonella nucula, Orthonota retusa, Murchisonia articulata, and Beyrichia 
tuberculata, all fossils of the Upper Ludlow rock. 
The detailed sections of the Norwegian strata are most valuable in demon- 
strating, by comparison, that the Silurian rocks of Norway are, from their base 
upwards, the true equivalents of those in Britain, and also in showing that 
the Alum-schists, like the ' Primordial ' Silurian strata, form the natural-history 
base of the Silurian system. The sections also demonstrate that, from this base 
to the uppermost beds, these zones (in all occupying less in the Christiania basin 
than 2000 feet in vertical dimensions) represent the whole of the vastly ex- 
panded British series, and constitute one conformable and natural system, 
whether viewed physically or zoologically f. 
Subsequently to the issue of the excellent work the ' Silurian Basin of Chris- 
tiania ' J, M. Kjerulf and M. Tellef Dahl pointed out that the whole of the above- 
mentioned Silurian deposits repose upon quartzose rocks (to the north of Chris- 
tiania) which in 1857 the authors referred to Cambrian age §. In a separate 
work they proved that the silver-ores of Kongsberg occur in crystalline rocks 
(whether gneissic, hornblendic slate, mica-schist, or quartz-rocks) which are 
older than the lowest Silurian ||. Another and more elaborate description of the 
Silurian basin of Christiania by Kjerulf himself followed in 1865% illustrated by 
* Quart. Journ. Greol. Soe. vol. iii. p. 34. 
t Judging from a collection transmitted by M. 
Kjerulf, and examined by Mr. Salter, the specific 
identification with the British forms may for the 
most part be depended upon. 
I Christiania Silur-Becken chemisch-geognos- 
tisch Untersucht (Christiania, 1855). 
$ Ueber die Greologie des siidlichen Norwegens 
(Christiania, 1857). 
|| Om Kongsbergs Erts District (Christiania, 
18(50). 
Vemser (Christiania, 1865). 
