Origin of tlic Archcan Igneous Rocks. — WincJuil. 
j^V 
rent evidence of other microscopic character. It is evident 
that in such a schist it would be ahnost impossible to -find 
augite retaining its crystalline form, for it readily changes to 
hornblende, that being indeed almost the first mineralogic 
change that takes place in a volcanic tufif of such age. But 
the augite cores remain in the schist, sometimes, as augite, 
and, on a still broader scale, the original forms of the augites 
are outlined in the resultant hornblendes by difference of ab- 
sorption and of colors between crossed nicols. Exactly the 
same characters are seen in the augites of the porphyry and 
granite-porphyry, where the preservrition is sufficiently perfect 
to disclose the gegyrine characters of the original augite. As 
to the sameness of the feldspars, with their peculiarities, there 
is no question. 
These two important characters ally these rocks in some 
way in a genetic bond, for the feldspars especially are wholly 
unlike any known elsewhere in the state. Chemical analysis 
points to anorthoclase, but the zoned structure, when analyzed 
by the microscope, indicates that the feldspars began as lab- 
radorite, passed to andesine, and, sometimes at least, termi- 
nated as albite, there being a continual increase in the acidity 
of the magma in which they were generated. 
The general aspect of the granite (seen in thin section) 
along the south side of Kekequabic lake is suggestive, not of 
crystallization from a magma, but of simple induration of 
coarse debris. The feldspar grains do not interlock, except as 
they have been enlarged by a secondary growth, and in many 
sections examined they do not even come into contact, but 
are separated, very generally, by a space which is occupied by 
a fine interlocked secondary development of feldspar and 
quartz. The margins of the feldspars frequently are inter- 
locked in this new growth. As this fi?ie matrix increases in 
amount, so the rock becomes porphyritic ; as it increases in 
coarseness, so the rock becomes granitic, but in all cases, or 
in nearly all, there is a distinct diiTerence between the old 
feldspars and the new. Along with this generation of new 
feldspathic material, is also the recrystallization of the quartz, 
thus making a truly granitic rock. The old feldspars, which 
in the schists proper, without metamorphosis have a tendency 
to disappear by a process of micro-granulitization into a fine 
