R.D. Lrving—FHornblende of the Northwestern States. 181 
The earliest microscopic work upon the erystalline rocks 
j¥ 
of the northwest that I have learned of was that of Mr. C. E. 
greenstones from the Keweenawan and older formations. e 
gabbro from Duluth, Minnesota, he describes as “ hornblende- 
gabbro,” it containing hornblende in addition to the augitie 
ingredient, though he does not regard the hornblende as sec- 
ondary in nature, which I think it undoubtedly is." 
In the same year Mr. C. E. Wright published descriptions of 
37 rocks from Central Wisconsin. A number of bornblendic 
schists are here included. but no mention is made of any 
Saw, though he never examined these rocks in the field. It is 
the only systematic treatise yet published upon the pone 
of this formation, and is one which will long be a standard, 
formation are nearly altogether diabase (using the Rosenbusch 
homenclature), contrary to the previously received views, and 
S th 
‘4 
M some of these he shows that there eccurs a uralitic altera- 
DP: 21393), oa te ORE ae a 
Parag Jahrbuch, 1877, p. 113; also R. Pumpelly, Geology of Wisconsin, — 
* Geology of Wisconsin, vol. ii, pp. 637-642. 
Geology of Wisconsin, vol. iii, pp. 600-656. 
