242 CRUISE OF THE NEPTUNE 
development on Davieau island and northward to McTavish 
island, where they have a thickness of fifty feet. These 
measures can be traced southward from the Nastapoka chain in 
the outer islands lying along the coast for upward of 150 miles, 
being last seen on Long island just north of Cape Jones, where 
they are overlaid by a considerable thickness of trap. 
The second division of the section is an arbitrary one, and 
was made to embrace all the beds containing important deposits 
of magnetite. The upper beds of the division grade into those 
of division I, while the lower pass gradually into division III. 
The typical rock of these measures is a dark-gray, fine- 
grained variety of quartzite chert, containing considerable mag- 
netite scattered through it in minute crystals; it also contains 
small quantities of carbonates of iron, magnesia and lime. The 
beds are usually thin (from one to twelve inches) and the part- 
ings between them are filled with a mixture of silica and 
magnetite with small quantities of ankerite. These partings 
vary in thickness, but are generally thin between the upper beds 
of the division, and quite thick (six inches to forty-eight 
inches) towards the bottom, where they form important ores of 
iron; as the beds of chert are often quite thin between two or 
more thick partings of ore, they might easily be neglected in 
mining. The mixture of silica and magnetite in the ore is an 
intimate one, with the silica usually in a finely divided state. 
The proportion of these substances is not constant, so that the 
ores vary from a lean ferruginous chert to a rich ore containing 
upwards of sixty per cent of iron. large quantities of the better 
ores occur in the lower beds of the division. The occurrence of 
these ores between the beds of gray siliceous rock, and their inti- 
mate association with finely divided silica, point to their 
deposition and enrichment from the infiltrations of waters 
carrying solutions of iron and silica which were deposited in 
the waters in cracks and between the bedding of the already- 
