483 
_the state of marble or highly ferriferous rocks; these strata are also 
abundantly interrupted by ridges of Trap and frequently cnverted, 
the carboniferous and Devonian deposits plunging under the older 
Grauwacke or Silurian rocks. 
Our authors also found that the Devonian strata reappeared in 
irregular troughs among the Silurian Grauwacke (often with in- 
verted inclination) in various parts of Nassau; many of the lime- 
stones, particularly on the river Lahn, being identical, both in 
structure and in coralline remains, with the beautiful marbles of 
Babbacombe, Torquay, and Plymouth. In many parts of this re- 
gion the strata are in a highly mineralized condition, copper and 
lead ores, as well as the more prevalent iron mines, occurring at 
intervals; whilst numberless eruptive rocks diversify the surface ; 
and the strata, particularly those of the Devonian age, alternate 
with a peculiar stratified contemporaneous trap-rock called ‘“‘ Schaal- 
stein,’ the more schistose varieties of which contain Devonian fossils. 
The various mineral waters of Nassau are supposed to be due to the 
last expiring effects of the same causes which produced, in former 
times, the numerous eruptions of Greenstone, Porphyry, and other 
igneous rocks. 
The quartz rock of the Taunus mountains, the southern limit of 
the region they examined, is considered to be an altered deposit of 
the Silurian epoch*. 
The authors next institute a comparison of the formations of 
Westphalia and Nassau with those of Liége, the Ardennes, and 
Eifel on the left bank of the Rhine. Starting from the country 
around Liége, which M. Dumont has rendered classic by his illus- 
trations and his map, Messrs. Sedgwick and Murchison confirm the 
' views of that author, and bear testimony to the great value of the 
method employed by him in bringing into symmetrical condition 
that highly tortuous and convulsed tract. They admit that he has 
most successfully demonstrated the replicatures of the different 
members of the Carboniferous and infra-carboniferous systems, and 
established on clear physical evidence, the fact that whole basins 
have been znverted. ‘They differ from him, however, in the compa- 
rison he has made between the older rocks of his own country and 
those types of classification which the authors have_ established in 
the British Isles. In his table of comparison, M. Dumont supposes 
that the Old red sandstone of England has no equivalent in Belgium, 
and that the formations which there occur beneath the Carbonife- 
rous limestone (his éerrain anthraxifere) are the equivalents of the 
Silurian system; our authors show that the psammites, schists, and 
* The most characteristic Devonian Mollusca are Strygocephalus, Gypi- 
dium, two or three species of Turritella, Euomphalus, the Terebratula of 
Devonshire, with the very peculiar trilobite, Brontes flabellifer of Goldfuss. 
The upper members of the Silurian system are distinguished by Orthoce- 
ratites, Homalonoti, and other Trilobites, Pterineze, Orthis, &c., some’ of 
which are identical with species found in the Silurian region ; with these 
are some remarkable forms not yet detected in the British Isles, such as 
Delthyris macroptera and D. microptera. 
