PUBLICATIONS. 711 
average dip of 8° or 10° a little east of south. The Animikie beds are 
interleaved with diabase sills. ‘These give parallel east and west ridges, 
the south sides of which are gentle slopes, and the north steep mural 
descents. This topography has led Lawson to the conclusion that the 
apparent large number of sills are due to monoclinal faulting of fewer 
layers, but of this there is no evidence. The Animikie strata are divided 
as follows: an upper or graywacke-slate member, 1goo feet thick, com- 
posed of slates and graywackes, with fine-grained quartzites and quartz- 
slates; a middle or black slate member, 1o50 feet thick, composed 
mainly of black slates, apparently carbonaceous, with a fine grained 
siliceous and flinty layer at the base 60 feet thick ; and a lower or iron- 
bearing member, composed largely of jaspery, actinolitic, siliceous and 
magnetitic slates, usually thinly laminated, and some beds of cherty 
iron carbonate. The Akeley Lake rocks, first called Pewabic quartzite, 
are similar to the Gunflint iron-bearing rocks and different from the 
Pewabic quartzite of the western Mesabi range, and if these iron-bearing 
rocks are put at the base of the Animikie, there seems to be serious 
objection to regarding them as the basal quartzite, and the equivalent 
of the quartzite of the western Mesabi range. No true quartzite 
is found at the base of the Animikie in the Akeley Lake area, but 
the iron-bearing rocks at Gunflint Lake rest directly upon the 
Keewatin. 
The quartzites of Pigeon Point are lithologically similar to the 
quartzite at the top of the graywacke-slate member, and are supposed 
to be equivalent to it. The igneous rocks are all intrusive. The 
diabase sills sometimes have a thickness of 100 feet. They have not 
been found in contact with nor to extend into the gabbro below. The 
great Keweenawan gabbro of the district has a varying mineralogical 
composition, sometimes being composed almost entirely of feldspar, 
thus forming anorthosite, and again being exceedingly rich in olivine. 
This gabbro includes fragments of the Animikie slates, and was found 
directly overlying and in contact with the uppermost member of the 
Animikie, thus showing it to be of post-Animikie age. Associated with 
the coarse-grained gabbros are finer grained rocks including gabbros, 
olivine-gabbros, norites and olivine-norites, which have been called 
muscovado. These are slightly older than the main mass of gabbro, 
which is seen cutting and including fragments of them. 
The acid eruptive rocks, called augite-syenite by Irving, including 
reddish, hornblendic, granitic rocks, are found cutting the gabbro. In 
