Baron Humboldt on Rock Formation^. 
or in general regarding that of all the primitive and transition 
rocksj we designate here, by the name of Volcanic Terrains, tJve 
least interrupted series of rocks altered by fire. 
In drawing up the enumeration of the diiforent rocks, I have 
made use of the names most generally employed by the geo- 
gnosts of France, Germany, England, and Italy : in attempt- 
ing to perfect the nomenclature of formations, I should be ap- 
prehensive of adding new difficulties to those which the discus- 
sion of relative positions already present. I have, however, care- 
fully avoided the denominations^ too long preserved, of under 
and u'pper limestone ; of gypsum of the Jirst, second^ or third 
formation^ of old and new red sandstone, &c. These denomina- 
tions without doubt present a true geognostical character ; they 
have relation, not to the composition of rocks, but to their rela- 
tive age. However, as the general type of the formations of 
Europe cannot be modelled after that of a single district, the 
necessity of admitting parallel formations ( sich mrtretende Ge~ 
hirgsarten ), renders the names of first or second gypsum, of old 
or middle sandstone, extremely vague and obscure. In one 
country it is proper to consider a bed of gypsum or of common 
sandstone as a particular formation ; while in another, it should 
be regarded as subordinate to neighbouring formations. Tho 
geographical denominations are without doubt the best ; they 
give rise to precise ideas of superposition. When it is said that 
a formation is identical with the porphyry of Christiania, the 
lias of Dorsetshire, the sandstone of Nebra (bunter sandstein)' 
the coarse limestone of Paris, these assertions leave no doubt 
in the mind of an experienced geognost, regarding the position 
which is to be assigned to the formation in question. It is also 
by silent convention, as it were, that the words zechstein of 
Thuringia, Derbyshire Limestone, Paris Formation, &c. have 
been introduced into mineralogical language. They express a 
limestone which immediately succeeds the red sandstone of the 
coal deposite, a transition limestone placed beneath the coal sand- 
stone, and lastly formations of more recent origin than the chalk. 
The only difficulties which the multiplicity of these geographical 
denominations presents, consist in the choice of names, and in 
the degree of certainty which may have been acquired, regard- 
ing the position or relative age of the rock to which the others 
2 
