and its associates on Lake Superior. 191 
gray. 
When ignited it loses 3-09 per cent of its weight, and changes 
toa light brown color. When digested with nitric acid, and 
afterwards with a weak solution of caustic potash (to remove 
free silica), it experiences, including the loss Vy ignition, a loss 
of 46°36 per cent. This consists of 
WENA oper scr ccereverie tae eros 14°73 
: Alumina, 717 
PeOTNO OF WOH Dae pics cee ue - 14°87 
: ime, 4°47 
: Magnesia, _..-_.. 2°03 
| ate 3°09 
46°36 
5 In the undecomposed residue light-red and dark-colored 
Particles are discernible. On digesting it with hydrochloric 
acid, and subsequently with a weak solution of potash, it sus- 
tains a further loss of 10-6 per cent, which consists of 
| Joe eee 3-48 
lng 3°03 
: Peroxide of iron, ..------ 1-98 
: _ ee eoepe Bere: 1°76 
: Moepness, ...5. 5 “35 
10°60 
_ The ‘undecomposed residue was still found to consist of a 
light red and a dark-colored constituent. The latter was the 
tuent, fused readily to a dark brown glass. To judge from its 
Sravity and fusibility, it would not appear unreasonable to 
"egard it as either pyroxene or hornblende. In quantity it did 
rade mrever, exceed one-eighth of the feldspar. The latter 
Hor xe magnetite, are : 
acid, it aoe reasonably be concluded that the constituents 
temoved by the nitric acid are those of the chloritic mineral. 
On treating the rock previous to ignition, much of the iron 1s 
_ Temoved as protoxide. 3 
