56 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
Tabulation of observations on orthoclase-bearing gabbros—Continued. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
a tropic bands of 
g the plagioclase 
2 Place a Macroscopic char- | Constituents as determined by in sections cut 
g . 3 acters. microscope, in order of age. at random in 
A 8 : the zone O: it. 
plaid ree 
& <] : ngles on| 2 .- 
i -i/2/a! & osite | oS 
2 ER es Se) | sides of] 4¢ 
1-2) oe \|aia Fy cross-hair.| & © 
° ° ° 
heed boos: Gre coseecs SE. | 29 | 51 |13W.| Medium-grained| Apatite, large and abundant; | 20 25 45 
to coarse-grain- labradorite; orthoclase; titani- | 16 21 37 
ed; resinous;| ferous magnetite; augite in| 12 13 25 
brownish; au-| long, twinned blades; dial-| 17 17 34 
gite in long radi- lage; ochre ; much secondnry 
ating blades. Sp. quartz. 
gr., 2.82. 
1057...| Bed of Cascade | S.4 | 10 | 62 | 2W.| Medium-grained;| Apatite; labradorite; ortho-| 21 18 39 
River, Minne- black-and-gray - clase; titaniferous magnetite; | 30 28 58 
sota; 12 miles mottled ; rough- diallagic augite,muchaltered; | 22 18 40 
from mouth. textured. Sp. secondary quartz. 
gr., 2.82. 
1062...) South side Eagle (abou|t)26 63 |2W.| Medium-grained| Apatite; labradorite; ortho-| 16 14 30 
Mountain. | (Not surveyed.) tocoarse; nearly | clase; augite, sparse, highly | 22 26 48 
black; rough. altered, and filled with dusty | 26 28 54 
magnetite (alteration-pro- 
duct?); secondary quartz. 
Hornblende-gabbro.— Along a belt of country, some fourteen to twenty 
miles in length, running westward from Bad River, Wisconsin, through parts 
of townships 44 and 45, ranges 3, 4, 5, and 6 west, at a horizon not far 
above the Huronian slates, exposures of a peculiar hornblende-gabbro 
have been noticed. This rock differs from the uralitic gabbros previously 
described in containing, instead of the fibrous, greenish, comparatively 
weakly dichroic uralite, a deep-brown, intensely absorptive, so-called 
basaltic hornblende. Some of these rocks have been described briefly by 
Pumpelly in the third volume of the Geology of Wisconsin,’ under the 
name of ‘“‘augite-diorite.” He regarded the hornblende as primary, and 
the rocks as intermediate between diabase and diorite, whence the name.” 
In the same volume I suggested that the hornblende was secondary, and 
that the rocks were merely altered gabbros.’ This opinion I find sustained 
by a re-examination of Pumpelly’s sections, and a study of a number of 
1Page 36. 2Page 170. 3Page 170. 
