SOUDAN FORMATION. 221 



soapstoue. With the other chang-es there has ahnost invariably been au 

 infiltration of iron oxide to a greater or less extent. Consequently this 

 contact phase of the greenstone is usually impregnated with iron oxide and 

 thereby colored red. To this fact the rock owes its name of paint rock, 

 a term which is very generally used by mining men for such altered 

 and red rocks. The plane of contact between the ore formation and the 

 greenstone has also been a plane along which actual movement has taken 

 place, and as a result a zone of bi'ecciation has been produced which 

 includes a certain thickness of both the iron formation on the one hand 

 and the soap rock or greenstone upon the other. The thickness of this 

 zone varies greatly. In some places practically no brecciation has taken 

 place, but in others there is a considerable thickness of brecciated rock 

 The production of slickensides along these cracks indicates movement even 

 in the greenstone at a considerable distance away from the immediate line 

 of contact with the iron formation. 



Immediately adjacent to the greenstone, and showing with it the 

 above-described irregular contact surface due to folding, lies the ore. Upon 

 this ore lies a capping of jasper. Both the ore and the jasper are very 

 much cracked, being penetrated by innumerable fractures, as is also the 

 greenstone, though, as a result of its brittle character, the cracks in the iron 

 formation are far more numerous and less continuous than those in the 

 greenstone. This fractured condition of the iron formation is clearly due 

 to compression resulting from the production of the close synclinal fold in 

 which the formation lies. Hence, since the ore as well as the jasper is 

 brecciated, there is no escape from the conclusion that the ore must have been 

 formed, in great part at least, prior to the time of the last folding of the 

 district which caused the fracturing of the rocks. The ore has been very 

 much broken up, and this breaking has been a great boon to the mining 

 company, as it makes it relatively easy to mine. For this reason, as has 

 already been stated, the ore is frequently designated a soft ore, although 

 this is, in a strict sense, a misnomer. In reality the various fragments of the 

 breccia are fragments of hard ore. This natural brecciation has been taken 

 advantage of by the efficient manager, and the system of mining which has 

 been developed here merely continues the natural process of brecciation, 

 and thereb}' the cost of winning the ore is greatly reduced. The method 

 of mining employed in the Chandler is described and illustrated on page 240. 



