28 R. D. Irving—Origin of the Hornblende of the 
variety, yielding greenish sections, but it shows all gradations 
from the fibrous forms generally regarded as characteristic of 
patie to sang non-fibrous, strongly cleaved, and deeply col- 
ored cryst. 
The first to notice augite in any of the northwestern crystal- 
line schists was Dr. A. Wichman, who in the third volume of 
the Geology of Wisconsin announces its occurrence, in a va- 
riety near to sahlite, in the hornblende-schists of the Huronian 
of the Menominee and Marquette regions of Wisconsin and 
Michigan.* He also noted its occurrence in a few sections of 
gneiss and mica-schist. Kalkowsky, however, had already 
made the same observation on certain European gneisses and 
mica-schists.t Shortly after the appearance of Wichman’s 
publications I studied the Flambeau River schists above men- 
tioned and found them to be identical with those described by 
him from the Menominee region, save that in some sections the 
augite assumes a greater importance. My suspicions were 
then aroused that all the hornblende of sins, rocks might be 
but a paramorphic product of the augite, and when, somewhat 
later, I came in conjunction with my assistant Mr. ‘Vanhise to 
study a suite of specimens ek a large area in the 
Worscan Valley, I was on the ou ook for evidence on this 
pot We soon a ene my tna patinndantly confirmed, 
or not only did we find augite occurring almost universally in 
the hornblendic gneisses and schists of this region, and even 
wholly replacing the hornblende, as above stated, but a num- 
ber of sections were observed in which the augite distinctly 
occurs as cores to the bamblente which is at times fibrous 
like uralite, but oftener is without fibrous character. 
Granites and Syenites.$~—The granites of this region are in 
considerable part merely dependencies of the gneisses, but irreg- 
pecs —_ of massive granite, plainly of an eruptive nature, ei 
r ese are sometimes mica-granites, but are also o 
Mest is 3s Nearly all sections ts studied of the latter kind 
of granite show augite as well as hornblende, and frequently in 
the shape of cores to the se ecg which appears not only 
of the uralitic and ordinary green varieties, but also in the kind 
known as basaltic, which yields shasaidaie dark-brown, very 
deeply absorptive sections. 
A prominent instance of a granite containing hornblende is 
the coarse-grained rock of Big Bull Falls on the Wisconsin River. 
The following is quoted from a summary description of the 
* Geology of Wisconsin, iii, pp. 606, 620, er ete. 
i Min. Mitt! ttheilungen, 1875, p. 4 
¢ These terms, as also those applied to the lies tocks below, are on in ac- 
cordance with the Rosenbusch nomenclature. 
