384 
SILURIA. 
[Chap. XV. 
Sedgwickii, Portlock ; G. Beckii, Barr. ; G. latus, M'Coy (?) ; G. spina, Bicht. ; 
G. turriculatus, Barr. ; G. Nilssoni, Barr. ; G. Sagittarius, His. ; G. colonus, G. 
Proteus, and Rastrites peregrinus, Barr.* ; with some other species common 
to this region and Bohemia, including the remarkable form Retiolites Geinit- 
zianus, Barr. Several of the Graptolites are similar to those of the Silurian 
deposits of Scandinavia, North America, and other countries. 
The researches of M. Richter have, indeed, gone further, and have enabled me 
to speculate upon a close approach to the Upper Silurian, if he has not really 
made known the base of that division. For among the remains of one of the 
courses of limestone, he has detected Cardiola interrupta, Brod., Acroculia pro- 
totypa, Phill., with Orthoceras styloideum and 0. Bohemicum of Barrande, 
both of which characterize the ' Stage e ' of that author. 
The Silurian rocks of the Thiiringerwald and of the Saalfeld tract, which are 
penetrated at intervals by porphyries and greenstones, are irregularly overlapped, 
towards their south-eastern flanks, by masses of Devonian age (the ' Rothe Grau- 
wacke ' of Richter), which will be considered presently. Silurian schists con- 
taining Graptolites again emerge from beneath younger strata in a series of low 
undulations far to the east of the lofty and wooded Thiiringerwald. The base, 
in fact, of the low ridges extending from Ronneburg on the north-east, through 
Schleitz, to Lobenstein on the south-west, is composed of graptolite-schists and 
roofing-slates. Similar rocks reappear in parallel undulations in the environs of 
Plauen and Hof ; and it is probable that considerable portions of the ' Thon- 
Schiefer ' of the Geological Map of Saxony will hereafter be found to belong to 
the Lower Silurian division. 
The exact demarcation of the outline of these Silurian formations, and their 
separation from all the older unfossiliferous and crystalline strata on the one 
hand, and from the Devonian locks on the other, will be a work of no small 
labour. Their regular order has been repeatedly interfered with by erupted 
and pseudo-volcanic masses, which, whether they constitute stratified layers or 
appear as intrusive bosses, have singularly affected the ordinary sediments. 
These igneous rocks are indeed most accurately laid down on the map by 
Professor Naumann and his associates. So rapidly does the geologist here 
proceed from one formation to another, that a single small hill composed of 
Lower Silurian schists with Graptolites is often contiguous to the Upper Devo- 
nian limestone. These changes are well seen near Schleitz, where the low 
ridges of black brittle schist, which form the pleasure-grounds of the reigning 
Prince (Heinrich's Ruhe), are laden with Graptolites, Orthidae, and other fossils 
of Lower-Silurian datef j whilst, on the western side of an intervening small 
hill of eruptive rock, the geologist has before him a limestone charged with 
Clymeniae, Cypridinae, and the very uppermost Devonian fossils ! On the whole, 
however, it may be said that, although they occupy so broad an area in the 
lofty tract of the Thiiringerwald, the Silurian rocks only make their appearance 
partially, and within comparatively narrow bounds, in the central portion of 
that region which has here been designated a vast undulating trough. Even 
then one characteristic band is alone visible, composed of the black schists and 
slates, extending from Ronneburg by Schleitz to Lehestein and Lobenstein. 
The Devonian rocks of this portion of Germany, previously known by the 
* See some of these forms of Graptolites, p. 61, by M. Berner, of Schleitz, who, it appears, de- 
and Plates I. and XII. of this work. tected Graptolites in these strata many years 
t All the Silurian fossils from this spot figured before the attention of geologists was called to 
in the work of Professor Geinitz had been found them. 
