388 
SILUKIA. 
[Chap. XV. 
Plant-bearing rocks also occupy a considerable strip of elevated country at 
the southern extremity of the Thiiringerwald between Sonneberg and Teusch- 
nitz ; and they occur in abundance in the gorge of the Steinach River, north 
of Koppelsdorf. As they offer a good ground for geological demarcation, I 
strongly urged M. Credner to distinguish his ' Jiingste Grauwacke ' from all 
its older associates which bear that unmeaning family name. As it will, of 
course, require much accuracy of local observation to draw the line between the 
plant-bearing rocks of Devonian and those of Carboniferous age, it will best 
become the progressive state of science not to attempt to draw any rigorous 
line between them, but to shade off on a map the colour of one rock into that 
of another, thus imitating the succession of nature, in which there can be no 
error. 
Such is an outline of the Palaeozoic succession of the last-mentioned 
diversified region of Central Germany, the complete elaboration of which 
calls for the full employment of the able men who are occupied in work- 
ing out its highly interesting features. A slight allusion only has been 
made to the south-eastern flank of the great undulating trough of Plauen, 
Schleitz, and Hof ; for, although Naumann and his associates have shown 
in their maps that older and more crystalline rocks appear, we have yet 
to learn how much of their ' primary clay-slate/ or ' Ur-Thonschiefer,' is 
to be grouped with the lower members of the series we have been con- 
sidering. Other inquirers may seek to ascertain to what extent many of 
these ancient schists and slates, evidently of sedimentary origin, have been 
converted into mica-schists, and even into the metalliferous ' gneiss,' amid 
which the illustrious Werner taught his lessons at Freiberg. 
It would seem presumptuous that a passing geologist should here hazard 
an opinion antagonistic to long-received ideas : still I venture to state that 
much of the so-called ' primitive gneiss ' in the plateaux around Freiberg 
is of a very different age from that of the Laurentian gneiss of America, 
Scotland, Bavaria, and Bohemia. I would indeed suggest that those por- 
tions of it which are separated by wayboards, and exhibit several of the 
features of bedding and jointing of aqueous deposits, will, like the quartzites 
and mica-schists of the north-western region of Scotland (p. 169), prove to 
be of no higher antiquity than some of the Lower Silurian formations. 
In the meantime, if we reason upon the fact that no Upper Silurian 
rocks exist here (abstracting from that category certain graptolite- schists, 
which may be considered their base), we may surmise that this region was 
raised above the waters and constituted dry land during a long period, 
and was afterwards depressed to great depths to receive accumulations of 
the Devonian era, at a period when, and in localities where, the bottom of 
the sea was powerfully agitated by volcanic action. 
This country also contains clear evidences of a phenomenon to which 
Professor Sedgwick and myself called attention in 1839 — namely, that 
whilst the ' older grauwacke ' (now known to be Lower Silurian), together 
with the Devonian and Lower Carboniferous series, have partaken of the 
