APPENDIX TO LITHOLOGICAL GEOLOGY.


sible to determine the method of issuance of a given rock, and
neither the term lava nor trap could be used in the restricted sense
here proposed, and there may be little fundamental distinction be-
tween the phenomena in the two cases. But both the distinction
and the terms are serviceable in geological literature, when stripped
of the pretentious clothing to which they have no title.
Prof. Dana has suggested that metamorphic rocks be designated
by the prefix meta-. If this were generally adopted, it would doubt-
less be serviceable. But the limitations of knowledge being such as
they are, it would seem almost necessary to introduce a correspond-
ing prefix to indicate similar rocks of igneous, or aqueous origin.
For if the simple name, as diorite, for example, be understood to
imply an igneous origin, and the compound term, mneta-diorite, a meta-
iuorphic one, it would be necessary, in the, very namning of the rock,
to assert an opinion as to its origin. But in many cases it is impos-
sible to positively determine the origin of a rock whose other char-
acteristics are very well known; and there would be no convenient
term to express this knowledge, without implying, knowledge not
possessed. In respect to granite, for instance, it is contended, sever-
ally, by able geologists, that it may have an igneous, an aqueous, or
a metamorphic origin, and yet, in many instances, the workingr
geologist would not feel at liberty to assert that a given granite
belonged to either class; and it would be a sore inconvenience to be
obliged to make an implied assertion upon the subject, or else be
shut out wholly from the use of the term granite.
If, therefore, the system of introducing prefixes to designate origin
be adopted at all, it should be complete, and yet leave the working
geologist at liberty to use the fundamental term, free from the added
signification. It is hence suggested that the term mneta- be used as a
prefix when it is desired briefly and conveniently to assert a meta-
morphic origin; that the prefix igno- be used similarly, to assert an
igneous origin; and aqao-, in like manner, to imply an aqueous origin;
while the simple terms shall have merely their own mineralogical or
other appropriate signification.
Class V Will then embrace the terms lava and trap, used to desig-
nate rocks of certain special eruptive origins, and a long list of
terms to which the prefixes meta-, igno- and aqibo- are attached, to
signify respectively metamorphic, igneous, and aqueous origin.
The foregoing terms furnish fair, though somewhat inadequate,
facilities for the designation of the several classes of properties indi-
cated under the headings.
There remains to be added a series of terms which shall express




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