Baron Humboldt on Rock Formations. 
inediary, secondary and tertiary deposites. The natural limits 
of these four systems of rocks are the clay-slate with glance- 
coal or ampelite and lydian stone, alternating with compact 
limestones and greywackes, the coal formation, and the forma- 
tions which immediately succeed the chalk. In geognosy, as * 
in descriptive botany, the subdivisions or small groups of 
families have more distinct characters than the great divisions 
or ^classes. It is the case with all the sciences; in which we rise 
from individuals to species, from species to genera, and from 
these to still higher degrees of abstraction. A method neces- 
sarily rests upon differently graduated abstractions^ and the pas- 
sages become more frequent in proportion as the characters are 
more complex. The transition or intermediary formations of 
Werner, which M. de Buch has first limited with the sagacity 
for which he is distinguished (Molfs Jahrb. 1798, b. ii. p. 254.), 
are connected by the ampelitic clay-slates, the syenites with zir- 
cons, the granite sometimes destitute of hornblende, and the an- 
thracitic mica-slate, with the primitive deposite ; while the small- 
grained greywackes and madreporous and compact limestones, 
connect them with the coal sandstones and limestones of the se- 
condary deposites. 
Porphyries of very different formations have their principal 
seat among the transition rocks ; but they break out, if we may 
so speak, in considerable masses towards the secondary depo- 
sites, where they are connected with the coal sandstone, while 
they penetrate into the primitive class only as subordinate rocks, 
and of little thickness. The progressive motion, or, if I may 
be allowed to use the expression, the extent of the oscilla-^ 
tion of the serpentine and euphotide, is very different. Those 
diallage rocks, constituting many distinct formations, rarely co- 
vered with other rocks, stop short nearly at the lower boundary 
of the secondary formations ; towards the bottom they penetrate 
into the primitive deposites to beyond the mica-schist. The 
chalk seems to present a natural limit to the tertiary formations, 
which were first characterised by Messrs Cuvier and Brongniart, 
and justly, as deposites entirely dilferent from the last secon- 
dary formations, described by the Freyberg School (Geogr. 
Miner, des Environs des FariSj p. 8. and 9.) Struck with 
the relations which exist between the tertiary deposites and 
