50 THE MAKQUETTE IKON-BEAEING DISTEICT. 



The first is known as tlie lower quartzite and tlie second as the upper 

 quartzite. Tlie lower (juartzite is often calcareous, <i'rading- in places into 

 a marble. Sometimes it is talcose. Occasionally it is interbedded with 

 arg-illite. The upper quartzite has none of the characteristics of the lower 

 bed, Init on the other hand it is frecpiently conglomeratic, at times passing 

 int(i a tnie conglomerate. The lower bed is rarely, if ever, ferruginous, 

 Avhile the upper one is composed, at several places, of alternate bands of 

 quartz and magnetite sands. The marbles, which are dolomitic in a large 

 measure, are regarded as a phase of the lower quartzite, whicli they overlie. 

 This marble is itsually siliceous, and is filled with crystals of calcite or 

 dolomite that 3-esemble orthoclase in appearance. 



The argillites and clay-slates are present in several beds, whose relations 

 to other l)eds will l)e mentioned later. These rocks are true slates, and 

 manv of theni are aljove the upper f[uartzite. 



The mica-schist group embraces a number of different rocks, whose 

 predominant feature is the possession of a micaceous constituent. .Some- 

 times they are more nearlv micaceous (piartzites than true schists. The 

 mica-schists often contain crystals of nndalusite, seams of l)lack hornblende, 

 and bunches of white quartz. Three horizons of the schists are noted, 

 the most im])ortant of which is near the top of the series in the western 

 portion of the district. 



The anthophyllite-schist lies innnediately below the liighest mica-schist 

 horizon. It is a slightly magnetic rock, varying in color from bro^^■nish 

 black to dull slate. It shows a tendency, in some places, to pass into 

 limonitic schists, and so may pass into a merchantable ore. Other horizons 

 of the schist are mentioned and their places in the series fixed. 



The carbonaceous shale may be a carljonaceous variety of the clay- 

 slate, with which it might appropriately be placed. It contains a large 

 quantity of graphite, which burns off when the rock is heated, and leaves 

 it white. 



After characterizing the lithological peculiarities of the rocks found in 

 the district, Brooks descriljes in detail each of the principal mines worked at 

 the time the survey was made. 



