Specimen num- 
ber. 
1976... 
2504... 
2506.. 
DETRITAL ROCKS. 
131 
Tabulation of microscopic observations upon sandstones, &c.—Continued. 
Place. 
From quarry on north 
side of Portage 
Lake, Michigan. 
Foot-wall sandstone 
at Nonesuch mine, 
Porcupine Mount- 
ains, Michigan. 
Nonesuch ‘vein 
rock,” Porcupine 
Mountains, Michi- 
gan. 
Quarter-section. 
SE. 
SE. 
SE. 
| Section. 
28 
| Township. 
55 
50 
| Range. 
34W. 
43 W. 
43W. 
Macroscopic descrip- 
Excessively fine- 
grained; dark-gray; 
thin-laminated; 
hard. 
Light reddish-brown, 
streaked with still 
lighter shades; fine- 
grained. 
Dark greenish-gray ; 
fine- to rather 
coarse-grained; 
carries small peb- 
bles of red felsite. 
Abundant minute 
flakes of copper are 
visible. 
Microscopic descriptions. 
and still other much rarer ones, de- 
rived from the basic rocks. The fine 
matrix is largely composed of angular 
quartz fragments, along with which 
are others again of porphyry matrix, 
and still others stained of so deep a red 
that it is difficult to tell their original 
nature. Calcite has filtered in along 
certain seams, where it is found 
coarsely crystalline. 
A very fine-grained rock. Subangular 
to rounded particles of quartz pre- 
dominate. The other constituent 
particles are porphyry and basaltic 
detritus, minute fragments of mus- 
covite, infiltrated epidote and quartz, 
and magnetite. 
Angular to rounded quartz particles 
are predominant. Associated with 
these are numerous fragments of 
porphyry matrix and a still larger 
proportion of basaltic detritus. There 
is also a good deal of fine quartz that 
appears to be infiltrated. 
This rock is composed of mingled por- 
phyry and basaltic detritus. The 
former presents itself in the shape of 
quartz grains (which are quite abun- 
dant), and fragments of the matrix 
and of porphyritic feldspars. In 
several instances fragments of a 
quartz-porphyry still containing por- 
phyritic quartzes areto be seen. The 
basaltic detritus, to whose presence 
the dark color of the rock is due, in- 
cludes pieces of amygdaloid matrix, 
particles of the coarser grained dia- 
bases, with the several constituents 
together; fragments of triclinic feld> 
spar; magnetite particles ; and green- 
ish particles, which are at times re- 
cognizable as highly altered augite 
and diallage. In the interstices be- 
tween the grains, which are from an- 
gular to round in shape, a fine detrital 
material is sometimes seen; but for 
the most part these spaces are occu- 
pied by infiltrated matter, in the 
shape of epidote, a greenish chlorite, 
