NATURAL HISTORY. 
views of Geognosy lean towards the idea of the 
liquified masses ascending from below upwards, 
whilst that of Werner explained every thing by 
precipitations, and movements in an opposite direc- 
tion ; he supposed them to have been dissolved in 
water, but the better opinion now seems to be, that 
their fluidity was caused by an increase in the 
temperature of the Earth; the researches and 
experiments of Mitscherlich, appears to give a 
high degree of probability to this Theory; he has 
produced by artificial fusion, upwards of forty dif- 
ferent species of minerals, the greater number of 
which, correspond precisely with those ascertained 
to exist in nature, and he thence argues ‘‘ that the 
artificial production of mica and other minerals 
which compose our primitive rocks, appear to place 
beyond doubt, the Theory that our primitive moun- 
tains were formerly a melted mass,” 
Humboldt also in his Geognostical Essay—in 
which he has embodied all his own immense per- 
sonal experience, and that of every other able 
geognost, ‘“‘dees not hesitate to range himself on 
the side of these who rather conceive the formation 
of crystallized siliceous rocks by fire than by wa 
ter.”? We have heard it suggested, that some part 
of our granite may belong to a later and Transition 
zera—but we see no reason whaiever for considering 
the whole of it to be other than of primitive and 
contemporaneous formation. 
The determination of the relative ages and origin 
ef the rocks included under the head of the Slate 
