284 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
The Agate Bay Group—The Agate Bay Group of beds is finely dis- 
played in its entire thickness of some 1,500 to 2,000 feet, along the lake 
shore for a distance of some 84 miles, between a point in the 8. W. 4 of 
See. 34, T. 51, R. 13 W., a mile and a half below the mouth of Lester 
River, and one in the S. E. 4 of Sec. 14, T. 54, R. 9 W., two miles above 
the mouth of Encampment River. These beds are also to be seen exposed 
on French, Knife, Encampment, and Gooseberry rivers, for short distances 
from their mouths. 
The most striking external characteristics of this group, as compared 
with those previously described, are the relative thinness and distinctness 
of its beds; the great number of highly vesicular amygdaloids, which 
must make up more than half the entire thickness of the group; the pe- 
culiar appearance of subordinate stratification presented by both amygda- 
loidal and compact portions of the layers, when weathered; the prevalent 
fine grain of all save one or two of the beds, and the presence of two or 
three thin layers of red sandstone, shale and conglomerate. 
The lower beds of this group, which are to be seen along the shore in 
Sees. 34, 35, 24, and 26, T. 51, R. 13 W., trending more to the northward 
than the coast and dipping southeast about 15°, are somewhat peculiar. 
The rocks exposed about the lower part of Encampment River in Sec. 11, 
T. 53, R.10 W., appear also to belong here, as do, in part, those along 
the shore for two or three miles above the mouth of the same river, the 
broad bay into which this river empties setting back far enough to reach 
these lower layers. The non-amygdaloidal portions of these lower beds 
are composed largely of very dense conchoidal-fracturing diabases of the 
ashbed type, some having a dark-greenish to black color, while others have 
a more reddish-brown color, when the grain is excessively fine. There is 
often more or less unindividualized material, when the rock becomes a 
diabase-porphyrite. Other layers again have the compact portions a coarser 
rock, often much altered and crumbly, and of various purple and brown 
shades. These are the usual Keweenawan fine-grained olivine-free diabases. 
The amygdaloids of all these beds are plainly marked. They carry chiefly 
laumontite, calcite and quartz in the cavities, which are often of large size 
(4 to 4 inch), smooth-walled, and elongated in a common direction. Many 
are empty, and being thickly strewn, the result is a completely honey- 
