Baron Humboldt on Rock Formations. 47 
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In announcing these ideas regarding the sense which should 
be attached to the words independent formations., when treating 
of the order of their position, we are very far from undervaluing 
the eminent services which the most rigorous oryctognostic exa- 
mination, the minute investigation of the composition of rocks, 
have rendered to modem geognosy, and especially to the know- 
kdge of the relative position of formations. Although, accord- 
ing to the discoveries of M. Haiiy, regarding the intimate 
nature of inorganic and crystallized substances, there does not 
exist, properly speaking, a passage or transition of one mineral 
species to another ; (Cordier, sur les Roches volcan., p. 33., and 
Berzelius, Noiiv. Syst de Mineral., p. HO.)? the passages of 
masses or pastes of rocks., are not limited to formations which 
are commonly distinguished by the name of Compound Rocks. 
Those which are thought simple, for example, the transition or 
secondary limestones, are partly amorphous varieties of mineral 
species, of which there exists a crystallized type, partly of aggre- 
gates of clay, carbon, &c.^ which cannot be submitted to any 
fixed determination. It is upon the variable proportions of 
these heterogeneous mixtures, that the passage of marly lime- 
stones to other schistose formations is founded. (Haiiy, Tableau 
comparatf de la Cristallographie, p. 27. — 30.) All the amor- 
phous pastes of rocks, however homogeneous they appear at first 
sighC the bases of porphyries and euphotides (serpentines), as 
well as those problematical black masses which constitute the ha- 
sanite (basalt) of the ancients, and which are not all greenstones 
surcharged with hornblende, are susceptible of being subjected to 
mechanical analysis. M. Cordier has applied this analysis in an 
ingenious manner to the diabases, dolerites, and other more re- 
cent volcanic productions. The most apparently minute orycto- 
gnostic examination, cannot be indifferent to the geognost who ex- 
amines the age of formations. It is by this examination that we 
are enabled to form a just idea of the progressive manner in which, 
by internal development, that is to say, by a very gradual change 
in the proportions of the elements of the mass, the passage is 
made from one rock to a neighbouring. ’The transition slates, 
whose structure appears at first so different from that of the gra- 
nites or porphyries, present to the attentive observer striking ex- 
amples of insen s’lble passages to granular rocks of porphyritic 
