ORE DEPOSITS OF DPPEE HURONIAN". 185 



sight of an open pit extending down 200 feet, part of tlie workings still 

 being roofed over by an enormons arcli of rock. All work in the district 

 is at present under ground.^ As a rule, the under-ground ^^^ork has not, thus 

 far, been carried to very great depth, the two deepest mines being the 

 Great Western and the Dunn, which are down, respectively, 700 and 720 

 feet. The others are down to depths varying from 100 to 450 feet, the 

 lowest figures being, as a. rule, for the youngest mines, the more important 

 ones having nearly reached the 400-foot level or passed beyond it. 



In the early mining days of the district an extensive system of 

 timbering was resorted to, but gradually, as the cost of timber increased 

 and this item became burdensome, careful attention was paid to this point, 

 and, where practicable, the system of caving or the system of filling was 

 introduced (Mastodon). At the present time most, if not all, of the 

 important producers are mined with open stopes, pillars being left only 

 when necessary. From this it would appear that the rocks had not been 

 much broken, but it should be borne in mind that the ore deposits them- 

 selves are later than the folding, and in the process of their formation many 

 of the cracks in the surrounding beds could have been filled with ore or 

 other material and the rocks thus quite rigidly united again. That 

 cementation has taken place is evident from an examination of almost any 

 hand specimen or slide, where one may see veins of infiltrated quartz 

 traversing them at various angles. The extremely wet character of the 

 Grreat Western Avould seem to indicate that locally the rocks ma)" still be 

 very much fissured. 



PROSPECTING. 



Owing to the imjjossibility, with our jjresent knowledge, of mapping 

 the various beds of the Upper Huronian, it is not jjossible to give any 

 directions with reference to the exact lines which should be followed in 

 searching for ore. However, since the areas which are underlain by 

 igneous rocks have been delimited, there is no longer any excuse for wast- 

 ing time and money in prospecting in these unpromising portions of the 

 district. Where indications point to considerable rock movements, and 

 where the sideritic rocks are found associated with impervious slates, 

 explorations are warranted. 



'This was written in 1896. Since then a large part of the Mansfield ore body has been stripped, 

 and this miiy be worked at present by open -cut methods. 



