BERNAEDSTON SERIES OF UPPER DEVONIAN. 267 



down in the limestone, and that the uppei" 3 feet of" the latter is tliiii-bedded 

 and lacks the forms found below, while it carries the peculiar annulate 

 crinoid stems found also ver}' abundantly in the quartzite al)ove. 



The shaly limestone is in places much fissured, and is cemented at 

 times with veins, one -fifth to two-fifths of an inch wide, of a completely 

 gi'anitoid mixture of quartz and muscovite, the plates of the latter extend- 

 ing quite across the vein, while the cemented rock still shows abundant 

 crinoid stems. The limestone contains : CaCOg, 1)8.38 ; FeoOg, 0.62 ; 

 SiOo, 1.00. 



The magnetite bed. — In the largest opening under the main group of 

 birches the limestone for the upper 3 inches is impregnated with magnetite, 

 and the quartzite above this is fossiliferous. Fifty feet north the ferruginous 

 horizon swells out to a thickness of 3i feet, 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, in one place garnetiferous, and 3 feet 

 thick. It is of limited extent, but furnishes blocks of ore not to be distin- 

 guished 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 qiiartz-schist, abounding in jiyrite, 

 much crushed, and having- the fissures covered with small, fresh rosettes of 

 gypsum crystals and with drusy crusts of a mineral of earlier fonuation, 

 now much decomposed, which seems to be prehnite ; but owing to the small 

 size of the crystals (one-fifth of an inch) and their altered state they could 

 not be certainly determined. The form of the crystals is peculiai*. It is as 

 if each were made up of half a dozen long, square pi'isms, bounded above 

 by a dome and placed side by side, producing a fonn like a section of a 

 thick saw blade or the milled edge of a coin. 



At the point where the magnetite is thickest — 3J feet — 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 grade above into a layer, 1 inch thick, of a compact, grayish- 

 black rock, rusting red and glistening under the lens with fine biotite. 

 Under the microscope it proved to be a granular limestone. (See 

 "Petrographical description," Nos. 8 and 10, ]). 289.) The rock grades 

 into the black pyiitous quartzite above: all the beds are so entirely 



