^^6 Baron Humboldt on Rock Formations. 
ral events, is not regulated by the uniform progress of time, and 
could not consequently give it measure. We see behind us a 
series of creations and destructions, by means of the strata of 
which the crust of the earth is composed. They give rise to the 
idea of so many distinct periods ; but these periods, so fertile in 
events, may have been very short, in comparison with the num- 
ber and importance of the results. Between the creations and 
destructions, on the other hand, we see nothing, however vast 
the intervals may be. There, where all is lost in the void of un- 
determined antiquity, the degrees of relative age have no appre- 
ciable value ; because the succession of phenomena has no longer 
the scale which relates to the division of time.” ( Memoires de 
TFistitut, for the year 1815, p. 4<7.) 
In the geognostical monography of a deposit of small extent, 
for example, the environs of a city, one cannot distinguish with 
sufficient minuteness the different beds which compose the local 
formations, shelving banks of sand and clay, the subdivisions of 
gypsums, the strata of marly and oolitic limestone, designated 
in England by the names of Purbeck Beds, Portland Stone, 
Coral Bag, Kelloway Bock, and Corn Brash, then acquire a great 
degree of importance. Thin beds of secondary and tertiary for- 
mations, containing assemblages of very characteristic fossil bo- 
dies, have furnished, as it were, a horizon to the geognost. In 
their prolongation, whatever occurs placed above or beneath in 
the order of the whole series, has been referred to one of them. 
Even the particular denominations by which beds are distin- 
guished, are of much importance in a geognostical description, 
however whimsical or improper may be their signification or 
their origin as taken from the language of miners. But while 
treating of the relative position of rocks on a surface of great 
extent, it is indispensably necessary to consider the formations 
or habitual associations of certain beds in a more general point 
of view. It is then that discretion and circumspection are more 
necessary in the distinction of rocks, and in their nomenclature. 
The work of M. Freiesleben on the Plains of Saxony, which 
are upwards of 700 square leagues in extent {Geogr. Besclir. des 
Ku'pferschiefergehhges., 1807 — 15), presents a beautiful model 
of the union of local observations and geognostical generaliza- 
tions. These generalizations, these attempts to simplify the system 
