438 COPPER BEARING ROCKS OF LAKE SUPERIOR. 
NOTE 8. 
(Page 46.) 
NATURE OF THE FELDSPATHIC INGREDIENT OF GABBRO FROM CLOQUET RIVER. 
The feldspar of specimen 1103, separated from the other ingredients by Thoulet’s 
method, gave 52.40 per cent. of silica, or almost exactly that of labradorite, the feld- 
spar indicated by the optical measurements, as will be seen by reference to the table 
on page 46. 
NOTE og. 
(Page 50.) 
NATURE OF THE FELDSPATHIC INGREDIENT OF THE GABBRO FROM NEAR THE MOUTH 
OF NIPIGON RIVER. 
The feldspar of specimen 1752, separated out by Thoulet’s method, yielded 49.28 
per cent. of silica. The optical measurements indicate anorthite. A separation of 
the feldspars into two parts by Thoulet’s method was tried, but without success. 
NOTE ro. 
(Page 113.) 
SECONDARY QUARTZ. 
The secondary quartz of the orthoclase-gabbros (p. 51), augite-syenites, and 
granitoid porphyries of the Keweenaw Series (p. 113) is chiefly of the kind called by 
Fouqué and Lévy (Minéralogie Micrographique, p. 193), “‘quartz de corrosion.” Some 
of the secondary quartz of the last-named rocks may also correspond to their “ quartz 
globulaire” (op. cit., p. 194), but I find nothing in their descriptions or figures which 
recalls the peculiar arborescent secondary quartz so commonly met with in the 
matrices of the Lake Superior felsitic porphyries (p. 92). 
NO GSE, ata. 
(Page 59.) 
ANORTHITE-ROCK, 
Since this account of the rock of the anorthite bowlders and masses, met with 
inclosed in the olivine-gabbro of the Minnesota coast, was put in type, the following 
analytical determinations have been made upon the anorthite: 
| | 22 B 
729 |729A|729B| 822 }822A| (single | 822 C 
| | crystal.) 
Silica (Si Oz). --...----- 
Alumina (Als Oz)...-- seoseee 
Iron protoxide (Fe 0). 
Famer(CaiO)ec-- ---ee= 
Magnesia (Mg 0) ..-.. ee 
Potash (Ke QO) ..-...--. nocBacel hes 
Soda (Naz O).....-- a 
Water (He 0) .--...... 
| 
No. 729 is from a great mass of anorthite surrounded by black olivine-gabbro, near 
the mouth of Split Rock River, on the Minnesota coast (see p. 59). The sample for 
