Fi2 THE JOURNAL OF GEOLOGY. 
passing toward the granitic rocks, at first a few small acid dykes are 
seen. ‘These increase in frequency in approaching the central mass of 
the granite, and at the edge of the mass apophyses can be traced 
directly from the granite into the gabbro. The dykes are not finer 
grained as a whole or at their edges, than the main mass, thus indicat- 
ing the heated condition of the gabbro when the dykes were intruded. 
It is concluded that while the granite is of later date than the gabbro, 
itis not much later, and was perhaps intruded before the complete 
solidification of the basic rock. 
Culver,’ in 1894, describes the rocks of Itasca county, Minn. The 
Pokegama quartzite was found to extend from the north end of 
Pokegama Lake northeasterly to the rapids of Prairie River. This 
rock is flat lying, with low southerly or southeasterly dip, and seems to 
have been bowed into a series of low flat arches. The lower beds are 
fine grained, hard and massive, although broken into cubical blocks. 
In the upper portions of the quartzite in many places is found a con- 
siderable quantity of iron ore. In cross section there are alternately 
sheets of ore and sheets of quartz. In the hand specimen these quartz 
layers show no grains. The structure is porous, and the quartz is 
usually stained red. Both the ore and quartz layers are exceedingly 
irregular, and are often interrupted or cut by each other. 
The Prairie River granite lies in a belt parallel to the Pokegama 
quartzite. It contains some bodies of schist, which are taken to indicate 
that the granite is eruptive. Thrust planes are numerous, and gen- 
erally have either vertical or very steep dips. 
On Big Fork River, a few miles above the mouth of Rice 
River, diorite was found, and also at Koochiching Falls in the 
Rainy River. Greenstones constitute the chief exposures between 
Rice River and Big Falls. They comprise beds which are purely 
eruptive, other beds which are consolidated tuffs, and other phases 
which it is not possible to place certainly in either class. The 
mica-schists constitute an immense series, extending on the Big Fork 
River from a point twelve miles below Little Falls to within fifteen 
miles of Rainy River. At various places the mica-schist is cut by 
granite. In passing from the mica-schist to the granite, the mica- 
schist becomes veined with a granite, which gradually increases in 
* Notes on the Geology of Itasca county, Minn., by G. E. CULVER. Geol. and 
Nat. Hist. Sur. of Minn., 22d Ann. Rep., Part VIII., pp. 97-114; 1894. 
