264 THE PENOKEE lEONBEARING SERIES. 



resulted from the folding. The contained fragments are exceedingly 

 angular, as would he expected, and give no indication of having undergone 

 any considerable change since the folding, except that their intei'spaces 

 are cemented with chert and iron carbonate which must subsequently have 

 iniiltrated. 



When these rocks are examined in thin section the relations of 

 the chert and carbonate are seen to be exactly like those in the Penokee 

 series. As a general rule there is a regularity of interlamination of the 

 two, but quite frequently also the cherty layers break across the belts 

 of carbonate in such a manner as to imply an introduction of silica 

 subsequent to the carbonata layers. This introduction may show merely 

 a rearrangement of the silica which was originally deposited in the rocks, 

 as explained with reference to the Penokee series, but it may imply 

 an actual introduction of silica from an extraneous source, that is, a sec- 

 ondary silicification. The siderite is often well crystallized in perfect 

 rhombohedra or oval forms (PI. xxv, Figs. 1 and 2). These rhomlx)liedra 

 often average larger than in the corresponding rocks of the Penokee district, 

 but, as in them, they are occasionally argillaceous. The chert also varies 

 greatly in the coarseness of its grains, rumiing from almost completely 

 amorphous to almost completely crystallized. The wholly amorphous con- 

 dition is, however, unusual. 



The ferruginous slates. — The ferruginous slates are always found asso- 

 ciated with the unaltered cherty carbonate. They are not known to be so 

 extensively developed as in thePenokee region. In microsccipical character 

 they differ from them only in that magnetite is relatively more abundant. 

 Their derivation from the iron carbonates is seen in all its phases. A 

 description of these stages of gradation would l)e but a repetition ot what 

 has been said as to similar rocks in the Penokee series and so will not here 

 be given. 



The ferruginous cherts. — (Pis. xxvi, xxvii and xxviii. Fig. 2.) — The ferru- 

 ginous cherts are almndant. They comjjrise all the phases described in the 

 Penokee series, and exhibit as finely their origin and nlso the character of the 

 brecciation which sometimes accompanies these concretionar}' forms. The 

 chief difference exhibited Ijy the ferruginous cherts of the Animikie from 



