40 The American Geologist. ■^"•^'' ^^'^'• 
ON THE PARAMORPHIC ALTERATION OF 
PYROXENE TO COMPACT HORNBLENDE. 
Bv C. H. Gordon, Seattle, Wash. 
A careful examination of the evidence thus far advanced 
to prove the derivation of compact hornblende from pyroxene 
is not altogether convincing since most of the phenomena ap- 
pealed to may be equally well explained on the theory of syn- 
chronous growth. Such for example are the occurrences cited 
by Hawes,* Irving, Van Hisef and others, of augite and com- 
pact hornblende side by side, or the latter developed in a zone 
about the augite Later G. H. Williams J refers to the evi- 
dence adduced by these writers as lacking in proof, and pre- 
sents a case where a core of hypersthene is surrounded by a 
zone of compact biown hornblende, tongues and shreds of the 
latter extending from the outer rim all through the hypersthene 
core. Emphasis is also placed on the manner in which "die 
minerals insensibly grade into each other, and on the presence 
of fine twinning lamellae which cut sharply across the minerals . 
Commenting upon this professor I(idings in his paper on 
the rocks of Electric peak and Sepulchre mountain, says:i5 "It 
is self-evident that thin edged portions of minerals with sim- 
ilar indices of refraction, which wedge out against one another 
within the space of a rock section appear to pass into one an- 
other by insensible gradations of color. This can be observed 
in the case of inclined contacts between hypersthene and feld- 
spar in which case there is no suspicion of an actual transition 
of substance or intermediate stage of chemical character . There 
is no direct evidence brought forward in the paper cited "iio 
show by the crystal outline of the mineral that the original 
form was that of pyroxene as in the case of uralite. The whole 
argument seems to the writer to hang on the fact that the horn- 
blende penetrates the pyroxene in tongues and shreds in which 
respect it resembles the paramorphism of pyroxene to uralite. 
From the writer's acquaintance with instances of undoubted 
* Mineralogy and Lithology of New Hampshire, pp. 57, 206. Plate VJI. 
Fig. 1. 1878. Hawes, G. W. 
f Geology of Wisconsin, \o\. Mi, x>p. 170, XS80. Amer. Jour. Sci., toI. 26. 
3rd. Ser. p. 27. /6W, vol. xxvii, 3rd Ser. p. 130. "Copper Bearing Rocks of 
Lake Superior," U. S, Geol. Surv. Mon. X, p. 259. 
t Amer. Jour. Sci., 3rd Ser., vol. xxviii, p. 259. 
§ U. S. Geological Survey, 12th Annual Report, Pt. I, pp. 610, et seq . 
Plate L, LI 
