THE tRON-BEARlNG .^I EMBER. 279 



ward for »oinv distiiiice with the rehitioiis wliich they (•crtaiiiK- liiivi- in their 

 higlier levels, and the dikes are found to have toloi"a,lde re<4idarity of dij)s, 

 inclined shafts, as sugiifested l)y Mr. J. Parke ( 'liainiino-, ooidd l)e sunk 

 in the lower slates close to tlie (juartzite, with crosscuts throuyli tlie (^uartzite 

 iutd the ore. 



What has been said in reference to the relations of the ore bodies to 

 the dikes, foot- wall quartzites, adjacent lean material, and methods of 

 mining- can be better understood by an examination of Pis. .\xx and xxxi. 



NatHre of the rocks oftJir Iron-hrariix/ mcnihrr (itVuiccut to tlic ore bodies. — 

 Before considering the proliable origin of the ores, it will l)e necessarv to 

 recall the character of the rocks of the ore-liearing- formation adjacent to 

 the ore as compared with the rock in the parts in which ore has not ))een 

 found, and also tlie kinds of rocks whicli occupy the upper horizons of 

 the formation through the area in whicli pa\ing mines occur. 



From the general description of the iron formation, j). I'.IS, and from 

 the tabulations, pp. 2ir)-220, it will be seen that the i-ocks west of Tylers 

 fork are actinolitic slates. The magnetite and actiiiolite are important in 

 quantity and the silica is always com|)letely crystallized. Also the rocks 

 east of the Sunday lake mines and west of the Presque Isle river are of the 

 same character, except that the (p;artz is not ah^ays wholh crxstallized. 

 The Iron-bearing member east of tiie Presque Lsle is treated in another 

 place. Also these actinolitic slates in the east and west end of the 

 Iron-bearing inendier constitute, so far as known, tlie whole mass of 

 the ore formation. The jiart of th(- iron formation wliich he;irs the ore 

 deposits contains throughout most of its extent no actiiiolite and magnetite. 

 Its eastern and western extremities do contain a little of these two minerals 

 through the few miles in which they grade into l)aireii actinolitic slates 

 farther east and west. Another strong contrast between tiie (lart of the 

 iron formation carrying the ore bodies and the liarreii portions is found in 

 making a cross section of the member The nature of tlie rocks in which 

 the ore deposits actualh' occur lias already been mentioned. Above these 

 ferruginous cherts, which bear bands and shots of ore and which often 

 grade into ore, are in most cases regularlv banded red ferruginous slates. 

 These slates have been already described, and here it is only necessary to 



