242 CKUISE 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- 



