Gabbroid Rocks of Mimiesota. — Winchell. 30; 
currences had been reported in the entire series of basic 
igneous rocks in which the mineral was not demonstrably de- 
rived from cordierite preexisting in some granite or gneiss, 
a portion of which had been torn from its place and enclosed 
in the eruptive rock at the time of its ascension. 
The only known occurrence of cordierite in basic granitoid 
rocks was described a few months ago by M. A. Lacroix in 
his interesting memoir entitled '"Le Gabbro du Pallet" (Bull. 
Carte Geol. France. No. 67. 1899). The cordierite here oc- 
curs in conditions very similar to those described above. That 
is to say, it is fountl in a noryte composed essentially of 
hypersthene, biotite. andesine, (often with oligoclase), mag- 
netite, cordierite and pyrrhotite, with frequently quartz and 
garnet. The accessor}- minerals are apatite, graphite, zircon, 
spinel, sillimanite and staurolite(?). The cordierite is often 
very abundant, and usually accompanied by garnet and spinel. 
Occasionally the cordierite is wholly free of inclusions and 
.twinning, but oftener both are present, and then pleochroic 
halos appear about the inclusions of zircon. 
It is clearly demonstrated by Prof. Lacroix that the cor- 
<lierite noryte of Pallet is the result of the absorption by a 
gabbro of an aluminous schist. This is shown nt)t only from 
a study of the rocks mineralogically and chemically, but also 
from the field relations. 
Several distinctions are to be noted between the cordierite 
noryte of Pallet, and that of Minnesota. First, and most im- 
])ortant, is the fact that the Minnesota type is more basic, since 
it is an acid type of the labradoritic series while that of Pallet 
is an acid type of the andesitic group. Indeed, in the former 
the calcium oxide is notably in excess of the sodium, while 
in the latter the reverse is true. The Minnesota rock is there- 
fore the most basic rock described hitherto, containing cor- 
dierite derived from the magma, since the two or three other 
occurrences described are relatively very potassic and acid. 
It contains bronzite (and enstatite) in place of the hypersthene 
found in the rock from Pallet, though the chemical composi- 
tion shows slightly less magnesia, and fully as much ferrous 
iron. The biotite of the Minnesota type is of the unusual type 
anomite*, while in that from Pallet the mica is presumably 
*The cordierite rf>ck described by M. Max Koch contains pheno- 
crysts of anomite. 
