716 THE JOURNAL OF GEOLOGY. 
Spurr,’ in 1894, gives an account of the rocks of the Mesabi district, 
and particularly of the iron-bearing rocks. 
The oldest formation of the district is the Keewatin, the most 
common rock of which is green schist, but associated with this, 
especially near the granites, are hornblende-schists and mica-schists. 
The schists have a regional cleavage, which is nearly uniform in trend, 
about N. 70° E. and nearly vertical. Next in age to the Keewatin 
schists is the hornblende-granite of the Giants Range. This range has 
an average width of about ten miles, and its direction is the same as 
that of the schistosity of the Keewatin rocks. The granite is intrusive 
in the schists, as shown by numerous fragments imbedded in it, by 
stringers of the granite in the schists, and the metamorphism of the 
schists adjacent to the granite. ' 
Unconformably upon the former is the Animikie series. The 
Animikie series has no marked folding, slaty cleavage or schistose 
structure. ‘The rocks of the series are in a gentle southern monocline, 
in a direction perhaps ro° or 15° East of South. This monocline has 
gentle undulations, with axes parallel to its dip, and in the Virginia 
area has been faulted. ‘The amount of disturbance is greater adjacent 
to the central part of the district, where are found the Keweenawan 
rocks. It is probable that the weight of the Keweenawan rocks has 
produced a sinking in the area south of the Animikie, and that this has 
produced the tilting. The Animikie series may be divided into three 
chief members: the Pewabic quartzite, the iron-bearing member and 
the upper slates. The Pewabic quartzite is a fragmental rock, indur- 
ated by the enlargement of quartz grains. It occasionally passes into 
a fine-grained conglomerate. The iron-bearing member is composed 
of peculiar rocks, presenting no resemblance to the Pewabic quartzite 
or to the upper slate. The upper slates are of great thickness, and 
have at their base an impure limestone, often dolomitized or sideritized. 
The part of the iron-bearing member from Pokegama Falls to 
Embarass Lake is called the Western Mesabi range, that from Embarass 
Lake to Gunflint Lake, the Eastern Mesabi range, and from Gunflint 
Lake east, the International Boundary area. ‘The description of the 
iron-bearing member below applies to the western part of the district. 
It has a thickness varying from 500 to 1000 feet, with an average of 
about 800 feet. The dip varies from less than 10° to as much as 30°, 
*The Iron-bearing Rocks of the Mesabi Range in Minnesota, by J. EDWARD 
SPuURR. Geol. and Nat. Hist. Sur. of Minn., Bull. X., p. 268, with geol. maps, 1894. 
