THE ORIGIN OF IGNEOUS ROCKS. 
173 
some extent chemically.* The incorrectness of this idea 
has been discussed by the writer in the paper on Electric 
peak.f 
It is evident in the case of the granular core at Crandall 
basin that the aplite dike, analysis 16, Table II, is similar 
in chemical composition to certain varieties of the rhyolite 
of the Yellowstone region, which form immense bodies on 
the surface of the earth, and may therefore exist in some 
place within the earth in large bodies where the crystalliza¬ 
tion may attain a coarse grain. 
The same is undoubtedly true for other varieties of the 
granite-porphyritic “ ganggesteine.” In fact, equivalents of 
a number of them may be found among the rocks classed as 
“volcanic” by Rosenbusch.I Their chemical equivalents 
occur as extrusive rocks and the differences between them 
are due to their mode of crystallization. 
If we seek the extrusive equivalents of the lamprophyric 
rocks we shall first have to discover their chemical character¬ 
istics. They are often considerably altered and carry more 
or less calcite, so that chemical analysis fails to show the 
original composition of the unaltered rock. Moreover, many 
analyses have been poorl}^ executed and are misleading. 
It is not to be expected, therefore, that a study of all of the 
analyses of lamprophyric rocks which have been collected by 
Roth in his tables will lead to very definite conclusions. 
One is somewhat surprised, nevertheless, to observe the wide 
range in composition which obtains for rocks which have 
been called minette and kersantite. 
Table VII shows the range in percentage of silica for each 
*Rosenbusch (H.) Mikro. Phys. d. Mas. Gest. 8°. Stuttgart, 1887, p. 
838; also “ Ueber die cliemischen Beziehungen der Eruptivgesteine.” 
Min. u. Petr. Mitth. 8°. Vienna, 1889, vol. 11, p. 147. 
flddings (J. P.) The Eruptive Rocks of Electric Peak and Sepulchre 
Mountain, Yellowstone National Park. Twelfth Annual Report of the 
U. S. Geological Survey. 8°. Washington, 1892, pp. 656, 657. 
t Rosenbusch (H.) Mikro. Phys. d. mas. gest. 8°. Stuttgart, 1886; 
p. 380, microgranite and granite-porphyry; p. 456, diorite-porphyrite 
and quartz-diorite-porphyrite. 
