Baron lliimboldt on Roch Formatmis. 49' 
Physique, vol. li. p. 162.), tlirows light at once, Upon the 
large crystals which are isolated and separated from the micro- 
scopic crystals entangled in the mass ; '^dly, On the mutual pass- 
ages of some rocks, superimposed the one upon the other ; ^dly, 
On the subordinate beds, which are of the same nature as one of 
the elements of the amorphous mass. All these phenomena are 
produced, if we may so speak, by internal development; by 
variation in the constituent parts of a heterogeneous mass. 
Crystalline molecules, invisible to the eye, occur enlarged and 
disengaged from the compact tissue of the paste ; by their as- 
semblage and mixture with new substances, they insensibly be- 
come intercalated beds of considerable thickness ; and not un- 
frequently they even become new rocks. 
It is the intercalated beds which especially merit the greatest 
attention. (Leonhard, Kopp and Gmrtner, Pi'O'pad. der Miner,, 
p. 158.) When two formations succeed each other imme- 
diately, it happens that the beds of the one begin at first to alter- 
nate with the beds of the other, until (after these precursors of 
a great change) the newest formation shows itself without any 
mixture of subordinate beds. (Buch, Geogn, Beoh„ vol. i. 
p. 104. 156.; Humboldt, Rel. Hist, vol, ii, p, 140.) The pro- 
gressive developments of the elements of a rock, may, conse- 
quently, have a great degree of induence upon the relative posi- 
tion of the mineral masses. Their effects belong to the province 
of geology ; but, in order to discover and appreciate them, the 
observer must call to his assistance oryctognogy. 
In exposing the intimate relations by which v/e often see the 
phenomena of composition connected with those of relative situa- 
tion, it has not been my intention to speak of the purely cryc- 
tognostic method, which considers rocks according to the ana- 
logy of their composition alone. {Journal des Mines, vol. xxxiv. 
No. 199.) In the classifications of this method, abstraction is 
made of every idea of superposition ; but they do not the less 
give rise to interesting observations regarding the constant assem- 
blage of certain minerals. A purely oryctognostic classification, 
multiplies the names of rocks more than is required by geognosy, 
when occupied with superposition alone. According to the 
changes which the mixed rocks undergo, a stratum of great ex- 
tent and thickness may contain (we must repeat it here) parts 
VOL. x. NO. 19. JAN. 1824. D 
