110 Mr. Dana on the Analosies between the 
from the parent rock, may not the same be true of sedimentary 
deposits of granitic origin? Does not analogy therefore author- 
ize the conclusion that granite rocks may be metamorphic as well 
as gneiss and mica slate ? 
The nodules of syenite, granite, &c., found in granite, Rents 
long been a puzzle to geologists. ‘They are imputed to the pow- 
er of segregation, and many are no doubt due to this cause—at 
least those which by their concentric structure, show that they. 
were formed by crystallization around a centre. But there are 
others without a trace of a concentric structure, of rounded and 
cobble-stone shapes, like the stones or boulders of the roads and 
fields. Why are they not imbedded stones or boulders? and why 
do they not prove that the granite which contains them is as much 
a metamorphic granite, as'the pebbles in a porphyry bed prove it 
to be a metamorphic porphyry? ‘The proof is at least more sat- 
isfactory than can be derived from a stratiform structure. 
The granitic materials have been subjected to a higher heat 
than the porphyritic, and to this we impute the more perfect re- 
sumption of the features belonging to the parent igneous rock. 
It may be remarked that a running lava stream sometimes in- 
cludes pebbles or boulders that may lie in its course. But these 
are rare and there is no danger of being led astray by such isola- 
ted cases. 
Our argument thus far appears to have established these princi- 
ples: that mica slate, gneiss and granite may be igneous rocks or 
they may be metamorphic rocks, and that the action of heat pro- 
ducing the metamorphic changes has been so effectual in some 
instances as to disguise entirely their derivative origin. 'T’o the 
rocks enumerated, the associated formations of syenite, protogine, 
talcose rock, argillite, 6c. should be added, as they are part of 
one and the same series and come under the same general laws. 
It has always been difficult to determine what place should be 
assigned to gneissoid granite—whether with granite as a purely 
igneous rock, or with gneiss as a metamorphic rock. But these 
views if true, show that the gneissoid or stratiform structure is no 
evidence of a deposit origin, and the question can no longer be, 
whether it should be associated with gneiss or granite. ‘The na- 
ture of each is to be settled independently. It may be said that 
we place things in more doubt than they were before. It is ad- 
mitted. 'The more reason for doubt we know, the better, if they 
