Chap. XV.] 
PALEOZOIC ROCKS OF GERMANY. 
381 
the highest grades, are known to pass through a metamorphosis. Now, M. Bar- 
rande has discovered, after examining multitudes of specimens, that the Trilobite 
or earliest Crustacean underwent a similar metamorphosis from the embryo to the 
adult state, and passed through many changes of form. In the genus Sao, for 
example, he has distinguished no less than eighteen stages of development of the 
same species, each stage being marked by an addition to the thoracic ribs of the 
animal j and he has thus taught us, by true natural proofs, that several so-called 
genera and many species named by cotemporary authors really belong to this 
one creature *. The same analysis of forms has, indeed, been extended by M. 
Barrande to other and higher deposits of the Silurian system ; for he has indi- 
cated twenty-two changes in his beautiful species Arethusina Koninckii of the 
Stage e ; and altogether he has found the phenomenon to hold good in thirty- 
four species of Trilobites in the Lower and Upper Silurian strata, there being 
seven metamorphoses in the genus Trinucleus alone ! He has even followed out 
his subject into other families, and has traced the fossil Nautilus from the egg, 
through twenty variations of form, to its completion with a perfect aperture to 
the shell ! 
In a word ; the work of M. Barrande will convince every one who studies it 
that we have now obtained quite as clear an insight into the earliest stages of 
life yet recognized upon the globe, as into the succession of those younger de- 
posits the secrets of which are so much more easily wrung from the less indu- 
rated stony records of nature. 
Palceozoic Rocks {Silurian, Devonian, Carboniferous, and Permian f) of Thu- 
ringia, Franconia, Saxony, and the adjacent Principalities. — The older sedimentary 
formations occupy a considerable region on the north-western flank of that de- 
vious chain of granitic, gneissose, and other crystalline rocks which, ranging 
from north-east to south-west, divides Saxony from Austria, and trends into the 
Fichtel-Gebirge of Bavaria. From that chain the deposits in question descend 
into and spread over a broad and comparatively low, undulating tract, which in 
its central part is cut through transversely by the River Saal as it flows from 
Hof on the north-east to Saalfeld on the south-west. On their western boundary, 
these sedimentary rocks again constitute some of the lofty eminences of the 
Southern Thiiringerwald, the whole succession under consideration having a 
dominant strike from south-west to north-east. In this way the younger strata 
may be said to occupy a broad trough, ranging lengthwise from Ronneburg and 
Gera on the north-east, by Schleitz, Plauen, and Hof, to Upper Franconia on 
the south-west ; whilst the older rocks of the series, rising up on either side, are 
often in a highly metamorphic state, but chiefly on the south-eastern flank of 
the depression. 
The first effort to coordinate the various sedimentary rocks of this region 
with their equivalents in the Rhenish Provinces and the British Isles was made 
in the year 1839, by Professor Sedgwick and myself J. We commenced our sur- 
vey by examining the mountainous elevations of old grauwacke in the Southern 
Thiiringerwald, and thence extended our observations to the younger shelly lime- 
stones of Upper Franconia, wherein Count Miinster had collected his ' transition' 
fossils. As the result, we indicated that which has proved to be the true gene- 
ral succession. We spoke, for example, of a slaty greywacke with greenish 
slate and quartzose flagstones and grits like those of the Longmynd, — of quartz- 
* See particularly Corda, ' Prodromus einer Mo- t For details of the Permian rocks of these 
nog. der Bohmischen Trilobiten/ in which the spe- tracts, see p. 313 et seq. 
cies Sao hirsuta, Barr., has leen divided into no I Trans. G-eol. Soc. Lond., 2nd ser., vol. vi. p. 
less than ten genera, and these again subdivided 296. 
into eighteen species ! 
