Metamorphic Up>jpev Devonian Rocks. 271 



mixture of quartz and mnscovite, the plates of the latter 

 extending quite across the vein, while the cemented rock still 

 shows abundant crinoid stems. The limestone contains : 



CaC0 3 98-38 Fe 2 3 0*62 Si0 2 1*00 



g. The Magnetite bed. — In the largest opening under the 

 main group of birches the limestone for the upper three inches 

 is impregnated with magnetite and the quartzite above this is 

 fossiliferous. Following this boundary north 15 meters the 

 ferruginous horizon swells out to a thickness of one meter and 

 is here represented by a bed of porous limonite. At the same 

 distance farther north it is a bed of fine-grained magnetite, 

 often pyritous, and in one place garnetiferous, and nearly a 

 meter thick. It is of limited extent, but furnishes blocks 

 of ore not to be distinguished from Laurentian magnetites. 

 Analysis indicates phosphorus as well as sulphur. 



A little farther north where the base of the quartzite is 

 exposed over the thickest magnetite, it is a dark gray quartz 

 schist, abounding in pyrite, much crushed, and the fissures 

 covered with small fresh rosettes of gypsum crystals, and with 

 drusy crusts of a mineral of earlier formation, now much 

 decomposed, which seems to be prehnite ; but from the small 

 size (5 mm ) of the crystals, and their altered state, they could 

 not be certainly, determined. The form of the crystals is 

 peculiar, as if each were made up of half a dozen long square 

 prisms bounded above by a dome and placed side by side, 

 producing a form like a section of a thick saw blade. 



At the point where the magnetite is thickest — one meter — 

 I exposed by digging, its contact with the limestone below and 

 with the quartzite above, and found it to pass gradually into 

 the white limestone below and to graduate above into a thick 

 layer (20 mm ) of a compact grayish black rock, rusting red and 

 glistening under the lens with fine biotite. Under the micro- 

 scope it proved to be a granular limestone with regularly dis- 

 seminated biotite scales, of so strong absorption that basal 

 sections are opaque except in the thinnest portions, and then 

 greenish brown. It is thus unlike all the micas of the region 

 and perhaps is phlogopite. The mica is abundantly and regu- 

 larly spread through the mass, exactly as in a whetstone 

 schist. A single crystal of hornblende, little coaly matter and 

 rust, the fragment of a punctate Brachiopod and the arm-piece 

 of a Crinoid occur in the slide. This rock graduates into the 

 black pyritous quartzite above ; all the beds are so entirely 

 continuous, and undisturbed, that it is impossible to think 

 of faulting, or any irregularity at the junction, any more than 

 at the opening farther south under the birches, where the 

 junction is equally undisturbed. The paleontological evidence 



