^8 Baron Humboldt on RocTc Formations. 
tion /3 ; and that /s, instead of showing itself as an indepen 
dent rock, placed between o& and y, is now nothing but a bed in 
et. It is thus, that, in Lower Silesia, the red-sandstone contains 
the formation of zechstein ; for the limestone of Bunzendorf, 
filled with impressions of fishes, and analogous to the bitumi« 
nous marl abounding in fishes of Thuringia, is entirely de- 
veloped in the coal-formation. (Buch, Beoh.yoX. i. p. 104. 157. ; 
Id. Reisenaeh Norwegen, vol. i. p. 158. ; Raumer, Gehirge von 
Nieder-schlcsieny p. 79-) M. Beudant, Voy. Miner.^ vol. iii. 
p. 183.,. has observed a similar phenomenon in Hungary. In 
other districts, for example, in Switzerland, at the southern ex- 
tremity of Saxony, the red-sandstone disappears entirely ; be- 
cause it is replaced, and, so to speak, overcome, by a prodigious 
development of greywacke or of alpine limestone. (Friesleben, 
Kupfersch. p. 109.) These effects of the alternation or unequal 
development of rocks, are so much the more worthy of attention, 
that their study may throw light upon some apparent deviations 
from a generally acknowledged type of superposition, and that 
it may serve to refer to a common type the series of position ob- 
served in very distant countries. 
In order to designate the formations composed of two rocks 
which alternate with another, I have generally preferred the 
words granite and gneiss^ syenite and greenstone^ to the 
more commonly adopted expressions of granite-gneiss^ syenite- 
greenstone. I was apprehensive that this last method of desig- 
nating formations composed of alternating rocks, might rather 
give rise to the idea of a passage from granite to gneiss, from 
syenite to greenstone. In fact, a geognost, whose works upon 
the trachytes of Germany have not been sufficiently appreciated, 
M. Nose, has already made use of the \NOYdL^ gTanite-jporphyries 
and porphyry-granites, to indicate varieties of structure and as- 
pect, to separate the porphyritic granites from porphyries, 
which, from the frequency of crystals imbedded in the mass, 
presents an aggregational, a true granitic structure. By adopt- 
ing the denominations of granite and gneiss, of syenite and por- 
phyry, of grey v/acke and porphyry, of limestone and clay-slate,, 
no doubt is left regarding the nature of the complex terms of 
the geognostical seiies 
f Ttanslaled from Essai Geognostique par Baron Alexandre de Humboldt, 
