210 THE PENOKEE IRONBEARING SERIES. 



Microscopical character of thr actinoHiic .slates (PI. xxiii, Figs. 3 and 4; 

 PI. XXIV, Figs. 1 and 2; PI. xxviii). — As already stated, the actinolitie rooks 

 of the third type above luacroscopicall}' described liave as their four main 

 constituents, quartz, hematite, magnetite, and actinoUte. In the hirge 

 exposures all of tliesc minerals are invariably found. In hand specimens 

 any one of them may be found, to the almost complete exclusion of the 

 others, and also all ])ossil)lc combinations of any two or three of them, and 

 of all together. The order — (piartz, iron oxide, and actinolite — expresses 

 their usual relative abundance, taking the exjjosures as a whole. However, 

 in the thin section, as would of course follow from the foregoing, any one 

 of the three may at times be the j)redominant constituent, while also any 

 one or two of them may be almost or (piite wanting. In order of time of 

 crystallization, the iron oxide is always the earliest of these constituents, 

 next the actinolite, and iinally the (piartz. Yet while tliis is true as a 

 general statement, it is not meant to iuiply that the crystallization of any 

 one constituent is tinished before tliat of the second one begins, for they 

 are, to a certain extent, simultaneous. The areas of iron oxide are the 

 freest fntm inclusion of the other two chief constituents. The actinolite 

 contains large (piantities of iron oxide, but e\erywhere penetrates the 

 rpiartz, a single needle of actinolite commonly cutting twi> or more indi- 

 viduals of (piartz, and hnally tlie quartz individuals include much magnetite 

 and actinolite. However, each one of the minerals is, in certain cases, 

 found to include both of the other two. In addition to these three main con- 

 stituents, chlorite and biotite are found as extensive alteration products of 

 the actinolite. The alteration products, i-lilorite and l)iotite, are alwaj-s in 

 minute flakes, .several or many individuals of the.se ininerals forming from 

 a siuii'lc needle or bladi' of actinolite. The mai;netite and hematite are 

 directly associated and p>robably formed at the same time. Occasionally 

 the hematitic ingredient is manifest macroscopically by the peculiai- steel v 

 luster characteristic of specular iron, or by a purplish tint to the powder of 

 very highly ferruginous varieties; but the analyses quoted above show that 

 this ingredient is at times c(tntained when neither microscopic nor macro- 

 scopic characters would suggest its piesence. It apj)ears to be intimately 

 associated with the magnetite, and occurring in aggregates of very minute 



