83 
Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase— 
Composition as determined by 
the microscope. 
Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
tropic bands of 
the plagioclase 
in sections cut 
at random in 
the zone O: ii. 
Labradorite, in small strips; 
augite, in small grains; green 
substance in clouds of granu- 
lar masses. 
Oligoclase ; augite, inaggregated 
grains; magnetite or titanifer- 
ous tron. 
Oligoclase; augite, in rounded |; 
grains; magnetite ; chloriteand 
quartz pseud-amygdules. 
Plagioclase, predominant; augite, 
in grains; magnetite. 
Oligoclase; augite, in grains; 
magnetite. 
Groundmass: — much stained 
with red ferrite; consists of 
plagioclase in minute tabular 
crystals; unindividualized sub- 
stance; magnetite; ferrite; 
augite, in very minute grains. 
Porphyriticingredients:—rare 
JSeldspars; altered augites. 
Oligoclase, both in the ground- 
mass and in rare porphyritic 
crystals; augite, abundant in 
grains; wnindividualized sub- 
stance; magnetite; ferrite; 
chlorite pseud-amygdules. 
Oligoclase, predominates ; augite, 
in grains; magnetite. 
DIABASE-PORPHYRITE. 
Continued, 
8 : 
E Place, g Dee eT char- 
A 8 . 
3 eee 
3 # /2\e] & 
8 a |/3/6| 8 
n So |n]|A!] & 
2 W!..| Potato River, Ash- 24) 46 |1W.| Nearly aphanitic; 
land County, compact; black; 
Wisconsin. conchoidal frac- 
ture. 
9W}..| Old Ironton trail, 34 | 46/1 W.| Fine-grained; com- 
Ashland County, pact; black; sub- 
Wisconsin. conchoidal frac- 
ture. Sp. gr., 2.98. 
386 S1.| Clam Falls district,| NW.| 24 | 37 |17 W.| Aphanitic; black; 
Polk County, conchoidal frac- 
Wisconsin. ture. 
393 S!.| Totogatig district, | SW. | 28 | 42 |11 W. Aphanitie; black. 
Douglas County, 
Wisconsin. 
426 S!.| Upper Saint Croix | SE. | 6 | 43 |aa-w. Fine-grained; 
district, Douglas black; conchoi- 
County, Wis. dal fracture. 
1......| Mouth of Brewery | SW. | 23 | 50 |14 W.) Aphanitic; choco- 
Creek, Duluth, late brown; 
Minn. 75 north, highly conchoi- 
1,850 west. dal fracture; 
carries very mi- 
nute porphyritic 
feldspars. 
ik yee Bed of Brewery | SE. | 22 | 50 |14 W.) Matrix black; aph- 
Creek, Duluth, anitic; thickly 
Minn. crowded with 
small red feld- 
spars one-six- 
teenth to one- 
fourth inch long; 
alsopseud-amyg- 
dules of epidote 
and calcite. 
45.....| Bed of French |NW.| 6 | 51 |12 W.) Very fine grained; 
River, Minne- dark-gray; con- 
sota. choidal fracture. 
Soe aiar Bed of Beaver| N. 2|55|8 W.! Nearly aphanitic; 
River, Minne- | line. black; conchoi- 
Bota. dal fracture. 
Angles on 
opposite | 
Stites of 
cross-hair. 
° ° 
4 8| 10 
3)0 4 
Aa 
Ey 8 4 
$ 
QD 
B 
° 
A 
BS 
B 
e 
- 
Ss 
Al4 5 
£ 5 4 
= 
a3 6 
2 7 
13 17 
8 8 
1R. Pumpelly, Geology of Wisconsin, Vol. III, pp. 37-38. 
18 
12 
30 
16 
