R. Pumpelly— Pseudomorphs of Chlorite. 17 
The conical poles for diamagnetic experiments were then 
screwed on. ese were portions of cones with an angle at 
vertex of about 60°, with the vertex considerably rounded off. 
They were one inch apart and the poles were opposite. Cur- 
rent 4°4 farads per second. 
At center of field between the poles, 12500 
On the axis near one pole, 32100 
On cone one inch from vertex, 11000 
On cylindrical portion of magnet 23 inches 
from the vertex of the cone, 5800 
These poles were now replaced by frustums of cones with 
flat ends, the original diameter of the iron, 2 inches, being re- 
duced at the end to 14 inches, and they were placed 4 inch 
apart. The field in this case between them was 61000, or 
nearly up to the maximum of magnetization of nickel at com- 
mon temperatures, and above that at high temperatures. 
Troy, April 1, 1875. 
Art. IIl—On Pseudomorphs of Chlorite after Garnet at the 
Spurr Mountain Iron Mine, Lake Superior; by RAPHAEL 
PoMPELLy. With Plate IL 
PsEUDOMORPHS of garnet occur in abundance in a bed of 
chloritic schist, just oyerlying the great magnetite bed of the 
Spurr-Michigamme iron range.* 
This schist is of Archzean age and belongs in the upper beds 
of the Huronian iron series. It is a very fine-grained, dark 
Se chlorite, which gives a light green streak and ope 
issolves in acids leaving a deposit of silica, and fuses B.B. on 
the edge to a black magnetic enamel (fus. = 4.) It is impreg- 
nated with octahedrons of magnetite, which rarely reach a diam- 
eter of one-eighth inch. Throughout the rock are scattered the 
pseudomorphs in very sharply defined rhombic-dodecahedrons of 
all sizes below 14 inches in diameter. Often perfect crystals 
can be easily detached from the matrix. 
bacon the crystals and polishing the surface of fracture, 
they are found to be changed more or less to chlorite, in some 
Imstances specimens an inch in size containing not more than five 
per cent of garnet, while in others 30-50 per cent of unaltered 
Mineral is presen 
The octahedral crystals of magnetite are scattered through 
the pseudomorphs. “They are visible to the naked eye, half 
*I am indebted to Dr. ne, and . No 
Se ede yep eer 
Am. Jour. Ser. Tarrp —_ > X, No. 55.—Jo.y, 1875. 
