152 THE rENOKEE IRON-BEARING SERIES. 



whole, nmcli finer grained than the slates just described and which do not 

 show the same separation into a coarser fraginental portion and a finer 

 interstitial ]iortion, show a liackgronnd which is composed mainly of 

 quartz, l)ut also contains usually more or less feldspar. In some sections 

 the feldspar particles are quite abundant, while in others they are 

 almost, or quite, wanting. Scattered through this background in vary- 

 ing (piantities in the different sections are gToen flakes of chloi'ite and 

 l)r()\vn ones of l)iotite, the chlorite predominating in some sections, the 

 biotite in others. 



The quartz ])articles as now constituted are minutely angular. How- 

 ever, many of the larger have very plainly marked fragmental cores whose 

 outlines are em])hasized bv films made up of minute flakes of chlorite and 

 biotite. It i.s exceedingly difficidt to say how nuich of the finer grained 

 quartz is of a fragmental origin. Judging from the sections of the coarser 

 grained varieties of phase 2, described immediately above, we conclude 

 that part of this finer silica is fragmental, but that part of it is also an 

 original crvstallizatiou. 



Tlie flakes of chlorite and biotite are usually quite small, l)ut very 

 well defined, though occasionally large sized scales of uniaxial chlorite are 

 seen. It is taken as j^robable that all of these two minerals, along with the 

 nonfragmeiUal silica, have resulted from the decomposition of a detrital 

 feldspathic material. At all e\ents, in some sections all three of the 

 minerals occur within the outlines of a single original feldspar fragment in 

 such ;i manner as to show tlieir (leri\ation from the feldspar. This is a 

 jH'ocess of alteration, ])articularly as regards the biotite, which, as shown 

 on a subsequent page, has l)een carried out in a very striking manner 

 among the slates of certain portions of the Upper slate member of this 

 disti'icf, fragmental feldspathic rocks having been thus altered to rocks 

 that would ordinariU' he taken as crystalline mica-schists. If this is also 

 the origin of the micaceous ingredients of the rocks now e-speciall}' 

 under consideration, we should expect feldspar trao-ments, recognizable 

 as such, to be present in an abundance standing in an inverse ratio to the 

 amount of chlorite and l)iotite present. Tiic thin sections sliow that this is 

 actually the case. In the most highl\- chloritic and biotitic vai'ieties there 

 is recognizable little or no feldspar. 



