45 
Baron Humboldt on Rock Formations. 
which occur in the same places. It is to discover these analo- 
gies of situation and relative position, that the labours of geo- 
gnosts should tend, who delight to investigate the laws of inor- 
ganic nature. In the following tables, we have attempted to 
unite all that is known with certainty, regarding the superposi- 
tion of rocks in the two Continents, to the north and south of 
the Equator. These t^pes ofjbrmatkins will not only be extend- 
ed, but also variously modified, in proportion as the number of 
travellers qualified to make geognostical observations shall be- 
come increased, and as complete monographs of different dis- 
tricts at great distances from each other shall furnish more pre- 
cise results. 
The exposition of the laws observed in the superposition of 
rocks, forms the most solid part of the science of geognosy. It 
must not be denied, that the observations of geognostical situa- 
tion often present great difficulties, when the point of contact of 
two neighbouring formations cannot be reached, or when they 
do not present a regular stratification, or when their relative situa- 
tion is not tmiform^ that is to say, when the strata of the upper 
deposits are not pffi’allel to the strata of the lower. But these 
difficulties (and this is one of the great advantages of observa- 
tions which embrace a considerable part of our planet), diminish 
in number, or disappear entirely, on comparing several districts 
of great extent. The superposition and relative age of rocks, 
are facts susceptible of being established immediately, like the 
-Structure of the organs of a vegetable, like the proportions of 
elements in chemical analysis, or like the elevation of a moun- 
tain above the level of the sea. True geognosy makes known 
the outer crust of the globe, such as it exists at the present 
day. It is a science as capable of certainty as any of the physi- 
cal descriptive sciences can be. On the other hand, all that re- 
lates to the ancient state of our planets, to those fluids which, it 
is said, held all the mineral substances in a state of revolution, 
to those seas wdiich w^e have raised to the summit of the Cordil- 
leras, to make them again disappear, is as uncertain as are the 
formation of the atmosphere of planets, the migrations of vege- 
tables, and the origin of different varieties of our species. Yet 
the period is not very remote when geologists occupied them- 
selves by preference with the solution of these almost impossi- 
