236 J. M. BELL 



deposition, whereas elsewhere the former still continued. In the 

 Pucaswa area no such close relation between the iron formation and 

 the Upper Huronian is apparent. 



The rocks of the Helen Formation consist of rusty, ferruginous, 

 banded cherts, banded jaspers, banded magnetic cherts, pyritic 

 cherts, sideritic cherts, and various griineritic, actinolitic, and horn- 

 blendic schists, resulting from their metamorphism, together with 

 phyllites, sideritic arkoses, and possibly quartzites. The Iron 

 Formation in the Pucaswa area consists of similar rocks, though 

 sideritic cherts are rare or wanting, and magnetic, banded chert is the 

 most common iron-bearing rock, whereas in the Michipicoten area 

 rusty, non-magnetic, banded chert is the prevailing species. 



The schists of both areas comprise chloritic schists, mica schists, 

 hornblende schists, carbonate schists, quartz-porphyry and felsite 

 schists, schistose agglomerates, and amphibolites. All of the schists 

 are intensely sheared, and some of them, particularly the finer- 

 grained varieties, are so evenly laminated that they very closely 

 resemble, and probably actually are, phyllites. Quartz-porphyry 

 schist, a nacreous sericitic rock containing blebs of glassy quartz 

 and sometimes gneissoid, very frequently borders the iron formation 

 in the Michipicoten area, and carbonate schists are also often in 

 close connection. Apart from this somewhat general definite position 

 occupied by these two schists, no exact horizons are held by any 

 other of the Lower Huronian schists. 



The Upper Huronian in the Michipicoten and Pucaswa areas 

 consists of the Dore Formation, comprising conglomerates, agglom- 

 erates, slates, and tuffs — the conglomerates being the commonest, 

 most significant, and most characteristic. The Dore conglomerate 

 is a very much mashed rock, with a fine-grained chloritic matrix, 

 containing within it rounded fragments of pre-existing rocks of all 

 sizes, from those scarcely visible to the eye, to others a foot or more 

 in diameter. The ground-mass is exceedingly schistose, and the cobbles 

 and pebbles included in it are all more or less elongated parallel to this 

 structure. The harder pebbles show only flattening, parallel to the 

 longer diameter, while the softer pebbles are often so attenuated that 

 they resemble long narrow ribbons, or else are so thoroughly com- 

 minuted as to be indistinguishable from the matrix proper. The 



