2i6 The American Geologist. October, looo 
nowhere outside of the gabbro area in Minnesota; but it oc- 
curs along the northern border of the state in the Rainy Lake 
region on the Canadian side of the boundary Hne. 
In many other gabbro areas in Canada the predominant 
rock is plagioclasyte. Thus it occurs in what has been 
termed the "Morin" area to the north of Montreal, in the 
Lakefield area, about St. Jerome, in the township of Kildare, 
on the east side of the township of Cathcart, near the pont des 
Dalles, near the village of St. Jean de Matha, in the township 
of Brandon; a very large area occurs about the head waters 
of the river Saguenay, which may be connected with the area 
about the head waters of the Moisie river. It is found at sev- 
eral points along the coast of Labrador, notably at Paul island. 
Two important plagioclasyte areas occur in New York and 
northern New Jersey. Outside of America, plagioclasytes are 
known to occur in large areas in Norway, where they have 
been termed labrador-rock or gabbro. They are known in 
several localities in the Archean regions of Russia, namely, 
near Kamenoi-Brod, in the Government of Kiew, in the Gov- 
ernment of Cherson, near St. Petersburg, etc. Finally they 
are reported from Egypt, v.'here they were used in the earliest 
historic times as material for statues and monuments. 
Exterior Characters. The plagioclasyte of Minnesota is 
remarkable for its freshness; it compares very favorably in 
this respect with the plagioclasytes from southern Canada, 
Labrador and Russia. The feldspar is frequently in large 
granular crystals, which give bright, glassy cleavage faces on 
which the twinning is usually very plain. The dull earthen 
appearance of decomposed feldspar is never seen except in the 
rock at the surface, which has suffered alteration from at- 
mospheric agencies. This form of alteration is common, but 
it is nearly the only decomposition which the rock has 
undergone, and it is never more than superficial. The color 
of the weathered feldspar is a dull white, sometimes greenish, 
but often also with a reddish tinge, due to the hematite, which 
is deposited along cleavage lines and curving fracture planes 
by percolating waters. This is the condition of the rock su- 
perficially at Carlton peak. The fresh unaltered rock does not 
present the play of colors seen on the well known labradorite 
