OLIVINITIC DIABASE—MELAPHYR. 73 
Tabulation of the results of a microscopic study of fine-grained olivinitic diabases (includ- 
ing melaphyrs). 
Angle between 
Maximum 6x- 
tinctions of 
adjacent hemi- 
* tropic bands of 
8 2 the plagioclase 
a Place. g Macroscopic char- | Constituents as determined by in sections cut 
5 3 acters. microscope, in order of age. at random in 
: 3 4 the zono O: ii. 
Be a | ° 
g £E|#| s |“opposita| 
2 ae eeiiisnla ides of| 4 q 
n COC ln |aH] & cross-hair. 
° ° ° 
“TheGreenstone,”| SE. | 19 | 58 |31W.| Medium-grained | Olivine, in ‘integral and aggre- 
Eagle River, Ke- to fine-grained ; gated grains, and, very rarely 
weenaw Point, very compact; | in crystals with recognizable 
Michigan.! hard and brit- though rounded contours,” 
tle; uneven to partly fresh, partly altered 
semi-conchoidal along fissures to a ‘‘ very pale- 
fracture; dark- green substance, sometimes 
green to green- tinged with brown”; anorthite, 
ish-black; ‘‘lus- ‘in very sharply defined and 
ter-mottlings” fresh, thin, tabular crystals 
3 to 3 inch in di- -001 to .002 inch thick and .01 
ameter; occa- inch and less long,” holding 
sional pinkish “scattering interpositions of 
porphyritic feld- an opaque black substance, 
spars 4 inch in which may be, or have been, 
length. Sp. gr., glass”; magnetite, in irreg- 
2.95. ular areas, moulded ‘‘ sharply 
around the contours of the 
feldspar and olivine”; augite, 
very fresh and transparent, 
relatively to the other ingredi- 
ents; in very large individ- 
uals, which often contain 
thousands of feldspars, but 
have crowded almost all of 
the olivine and augite into 
the interstices; residuary 
magma, largely altered to 
greenish, feebly polarizing 
substance, filling interstices 
between the feldspars not oc- 
cupied by sugite and pene- 
trating the feldspars in cracks. 
Lower zone Mar- | NW.| 19 | 58 |31W.) Fine-grained to | Olivine, wholly altered to a soft, AT 
vine’s bed 64;? aphanitic; dark- dark-green mineral; anorthite, 64 
Eagle River, green to nearly in small crystals; augite, 67 
Keweenaw black. SiO,, 47.74., fresh, subordinate; titanifer- 73 
Point, Michi- Sp. gr., 2.69. ous magnetite. 74 
gan.3 
egg ee ee ee eee ee ee eee 
1R. Pumpelly, in Metasomatic Development, p. 261. 
2 Geology of Michigan, Vol. I, Part II. 
*R. Pumpelly, Metasomatic Development, pp. 291-293. 
