SECTION FROM EAGLE RIVER TO THE EASTERN SANDSTONE. 17% 
fusible matrix, abundant porphyritic red feldspars, often as much as one- 
fourth inch in length, many of which are striated. Minute dark-green spots 
and an occasional tendency in the base to a finely crystalline texture are 
brought out by the lens. A vein carrying copper sulphide was formerly 
worked here, and the erystals of the porphyry occasionally carry native 
copper and silver in minute flakes along the cleavage planes.’ This por- 
phyry contains 59.52 per cent. of silica. Its thin section shows as porphy- 
ritic ingredients, oligoclase, less abundant orthoclase, much altered augite, 
apatite in large crystals, and magnetite. The matrix appears in the thin sec- 
tion to be composed of a translucent mineral much stained with red iron 
oxide, abundant black and red particles, and more minute and rare green 
ones. The principal mineral appears to be orthoclase, the opaque particles 
magnetite and ferrite, the green ones altered augite. From the older mine 
workings near these porphyry exposures, much typical prehnitized amyg- 
daloid has been thrown out, showing that we have such rocks continuing 
close to the porphyry. A short distance down stream from the old mine 
workings the Eastern Sandstone comes in. 
From the line of the Kingston conglomerate to the Suffolk or Prays- 
ville porphyry just described is a distance of about two and a half miles, 
At the usual 30° angle of dip, which holds everywhere north of the 
Kingston conglomerate, this would add some 6,600 feet in thickness to the 
section I have been describing. At the Suffolk location the dip was very 
unsatisfactorily made out, but further east the Bohemian Range shows higher 
dips than are met with in the more northern ridges, and we may reasonably 
suppose the same to be the case here. Allowing for this, the last-named 
figures should probably be increased to some 8,000 feet. The following is 
a summary of the section thus described, from the northern trap, off the 
mouth of Eagle River, at right angles to the general trend, and in a S. 28° E. 
direction, to the Eastern Sandstone: 
Thickness in feet. 
The Great Conglomerate, from the outer trap reef, off the mouth of Eagle 
River, and including the sandstone at base................-........-- 2, 200 
SA TUF DTI CTRL 1) AGES oe a SO A ee Pe 1, 417 
‘As to this, see R. Pumpelly, Geological Survey of Michigan, Vol. I, Part II, p. 39. The ex- 
posures are much more satisfactory now than at the time of Pumpelly’s examination, owing to the 
draining of the mill pond and destruction of the old saw mill at this place. 
12LS8 
