Gabbroid Rocks of Minnesota. — Winchell. 28 1 
I II III IV 
SiOg 
40.78 
47.40 
53-43 
46.24 
TiO, 
AUOs 
29-37 
29.74 
28.01 
29.85 
Fe.Og 
■34 
•75 
1.30 
FeO 
.60 
1.94 
2.12 
MnO 
.08 
trace 
MgO 
1. 01 
•57 
•63 
2.41 
CaO 
11.86 
13.30 
11.24 
16.24 
Na^O 
4-39 
4-99 
4.85 
1.98 
K2O 
.46 
1.56 
.96 
.18 
H2O 
1.76 
1.64 
traceCO 
a 1.03 
9Q.80 
101.14 
99.87 
101.35 
Sp. Gr 
.•2.676 
2.704 
2.673 
2.85 
I. Plagioclasyte from Carlton peak, Minn. No appreciable traces 
of BaO, SrO, nor TiOa . PiiOs not determined. 
II. Plagioclasyte from near Encampment island, Minn.; By C. 
Palache, Univ. of Calif. See A. C. Lawson: Bull. No. 8. Geol. & 
Nat. Hist. Surv. Minn. 1893. p. 6. 
Ill Plagioclasyte from near Nnin, Labrador; b3' A. Wichman; 
Zeitsch. d.d. Geol. Gesell. 188/j. 
IV. Plagioclasyte from mouth of Seine river. Out., by William 
Lawson; Reported by A. P. Coleman. Jour. Geol. IV. 1896. p. 907-11. 
Repeated tests for titanium gave uniformly a negative re- 
sult. It is not considered probable that this difference from 
the other gabbros will prove constant. No test was made for 
phosphoric acid, but, from the extreme rarity and small size 
of the apatite crystals, no more than a trace would be found. 
No appreciable amount of barium or strontium exists in the 
rock; no test was made for lithiimi. The rock has, as a whole, 
the composition of labradorite, which is natural, since at least 
nine-tenths of the rock is pure feldspar. 
Chapter V. Troctolytc. 
Troctolyte is the name proposed by Bonney* in 1885 to 
designate a rock essentially composed of olivine and plagio- 
clase, with very subordinate diallage. The German term for- 
ellenstein is applied to a rock of practically the same compo- 
sition. The rock styled troctolyte in this article has the typi- 
*T. G. Bonney: Geol. Mag. 1S85. p. 439. Ret. Kemp. Handbook 
of Rocks, p. 168. 
