Crystalline Rocks of the Northwestern States. 31 
where they occur on a grand scale in what has been called by 
Hunt the ‘‘Animikie Group.” This group has been. described 
by Logan, Bell and others as the lower part of the Copper-bear- 
ing series, and by Hunt as much newer than the latter series, 
but it is plainly, as I have elsewhere tried to show,* the exact 
equivalent of the Huronian of the Penokee region, and of the 
most important, occurring not only in dike-form, but also in 
ae SLs origin for the hornblende was entertained. So 
ar as later investigations have progressed the indications are 
that the hornblende of these rocks also is secondary. 
he greenstones of the Animikie group are displayed in a 
magnificent way along the shores of Thunder Bay, and inland 
to the west and north from there, occurring both in dikes and 
in great interbedded sheets. These greenstones include several 
varieties of gabbro and several of diabase, which I have else- 
where described.| Hornblende is not often met with in sections 
of these rocks, but when occurring seems always to be beyond 
‘question secondary. 
The Keweenawan greenstones include several varieties of 
‘each gabbro and diabase. I have described them in detail 
elsewhere.{ Hornblende on the whole is unusual in any of 
these rocks, but when it occurs it is almost invariably uralite ; 
that is, plainly secondary to augite. In the sections of one— 
unusual variety of gabbro met with in Ashland County, Wis- 
‘consin, which I have described as hornblende-gabbro,** in place 
‘of the ordinary uralite, or in addition to it, there occurs a deep 
* Third Annual Report of the Director of the U. S. Geol. Survey, pp. 159-163. 
Also “ Copper-Bearing Rocks of Lake Superior,” pp. 367-386. 
+ These interbedded diabases of the Huronian have been described by Brooks 
“and others as metamorphic, but there can I think be no question as to their 
eruptive origin. ¢ Geol. of Wis., iv, p. 607. 
; Geol. of Wis., iii, p. 628. 
r of the U. S. Geological Survey, pp. 
157-163; also, more completely in my memoir on the ee ok Rocks of 
op. ei 
** Copper-Bearing Rocks of Lake Superior, pp. 56-58. 
