THE EAGLE RIVER SECTION. Lis 
crystals, a soft, green mineral, probably pseudomorphous after olivine, minute graing 
of augite, and occasional small, often wedge-shaped, occurrences of a green soft sub" 
stance occupying the interstices between feldspar crystals.' 
According to the same authority, the amygdaloid of this bed 
has about sixty per cent. of its volume occupied by amygdules, sometimes wholly 
prehnite, sometimes an outer layer of white prehnite, and a central filling of calcite. 
The matrix is chocolate-brown, and has a crystalline texture wholly foreign to the 
melaphyrs, and more resembling that of a fine-grained, somewhat oxidized spathic 
iron ore.” 
This matrix is seen under the microscope to be almost wholly altered 
to prehnite, with abundance of particles of iron oxide. The amygdaloid of 
bed 65 is the layer so well known as the Ashbed, though the name is cer- 
tainly a misnomer so far as it means to indicate an origin in the condition 
of voleanic ash. The Ashbed has been much worked for the copper it car- 
ries. As already described, this bed is a peculiar mixture of sandstone and 
amygdaloid. 
Below the Ashbed Group comes next a thickness of 925 feet (constitut- 
ing Marvine’s group “a? beds 67 to 90, inclusive). This includes a series of 
beds mostly of very considerable thickness, ranging, for the most part, 
between 40 and 80 feet, while several are 100 to 150 feet thick. The upper 
members of the series are made up of ‘‘a rather coarse and not closely- 
textured” rock, which is “tough but not brittle, breaking with a rough frac- 
ture. The colors are dirty light-green, strongly mottled with quite well-de- 
fined spots of dark-green, * * * .” ‘The specific gravity is 2.87. The 
“capping amygdaloids are not very strongly developed.” One of these lay- 
ers (69) has been examined microscopically by Pumpelly.4 This bed 
consists of 56 feet of the lower zone, 11 feet of pseud-amygdaloid, and 6 feet of 
amygdaloid. The lower zone is a fine-grained, dirty-green rock with uneven fract- 
ure. It is easily scratched, has specific gravity 2.87-2.95, and the powder yields 
a little magnetite. The thin sections resemble those of the lower zone of bed 87. 
The plagioclase is much altered—containing in the freshest many tufts of chlo- 
rite—and is often represented only by pseudomorphs of chlorite, and in places these 
are merged into chlorite pseudo-amygdules. The augite is in part very fresh, 
in part changed to its characteristic pseudomorph. The amygdaloid is a very 
compact, hard rock, with subconchoidal fracture. It consists of very irregularly 
‘Proc. Am. Acad. Sci., Vol. XIII, p. 291. 
2Proc. Am. Acad. Sci., Vol. XIII, p. 290. 
3Geol. Surv. of Mich., Vol. I, Part II, p. 101 
4Proc. Am. Acad. Sci., Vol. XIII, p. 288. 
