Review of Recent Geological Literature. 371 
The key-note of the interesting discussion of the Vermilion and 
Keewatin ores is contained in the statement that the Vermilion magnet- 
ites are embraced in the schists immediately superimposed upon the 
Laurentian gneiss. They are believed to be due to hydro-thermal 
forces acting within the earth's crust on sediments and iron ores which 
were nearly in the condition of the rocks of the Keewatin series which 
is that next following the Vermilion. This fact is assumed, and the 
following comparative tables of the constitution of the Keewatin and 
Vermilion rocks open the subject. 
Keewatin. Vermilion. 
A chloritic mineral. A horblendic mineral. 
A sericitic mineral. A micaceous mineral. 
A feldspathic mineral A feldspathic mineral 
(generally plagioclase). (frequently orthoclase). 
Hematite iron ore. Magnetite iron ore. 
Good reason is shown for supposing that the change from chlorite to 
hornblende may take place by the loss of water and the absorption of 
lime. The evolution of the Vermilion biotite through hydrobiotite, and 
hydroinuscovite, to muscovite are ascribed to hydrothermal action. The 
change from plagioclase to orthoclase is accounted for by heated alka- 
line solutions reaching the mineral while under partial or complete 
hydrothermal fusion. That magnetite can result from hematite through 
the agency of heat and moisture is taken as one of the commonest 
phenomena of metamorphism. 
The Keewatin rocks are defined as of original volcanic origin as tuffs, 
altered and deposited by the hot Keewatin ocean. 
A description of diamond drill holes near Tower, shows the frequent 
alternation of the" schist with the ore and jaspityte. A well executed 
plate of four colored sections represents the studies of Dr. Hensoldt of 
some of these rocks. 
But the main point contended for, viz: that there has been a com- 
pleted cycle of evolution of the Biotite through Hydrobiotite to Musco- 
vite and back again to Biotite, that the Keewatin type has changed to 
the Vermilion and back again to the Keewatin by the recurrence of 
similar agencies, is a strong corroboration of the theory of cyclomor- 
phism which was emphasized in a paper read before the British Ass'n 
in 1888 entitled, "The nucleal ranges of the Antilles," wherein it was 
shown that just such complete cycles of change had been passed through 
by the crystalline rocks of Cuba. 
It is interesting in this connection to note the correspondence of the 
association of red and purple jasper nodules occurring throughout the 
green schist with the same phenomenon described by the writer in the 
geological survey reports of Penna. and named by him "Mountain 
Creek rock," because found abundantly along the Mountain creek of 
South mountain in Cumberland, Adams, Franklin and York counties, 
Penna. In this latter region the average size of these fragments is much 
less than in Minn., but occasionally there would be found amass several 
feet in diameter. It was found also impossible to draw a distinction in 
age between the red and amethyst (or purple) quartz fragments and I lie 
