10 Field Museum of Natural History 



ore cars run on a tramway to the shaft. At the shaft 

 tliey are run on to the cage and taken to the surface. 

 The broken ore in the stope not only provides a work- 

 ing platform for the miners but also serves in place of 

 timbers to keep the sides of the opening apart. At the 

 upper left corner of one of the stopes a small raise has 

 been driven to the level above for ventilation. 



When all the ore has been broken, the continued 

 withdrawal of the broken ore from below would leave 

 the stope empty. Left empty it would in time cave 

 and the motion of the rock thus produced might dis- 

 turb other workings of the mine. To avoid this after 

 the stope has been completed, as fast as ore is drawn 

 from below, waste rock is brought from the surface 

 to the fifty foot level and fed into the stope through 

 this ventilation-raise. The stope will thus remain full 

 even after all ore has been withdrawn. On the upper 

 level there are a number of worked out stopes which 

 have been filled from the surface. Not all stopes are 

 thus filled however, since in many cases conditions are 

 such that caving will do no harm, and there are some- 

 times other reasons for leaving them empty. In some 

 systems of mining caving is even invited and is so 

 controlled as to be of great assistance to the mining 

 operations. 



On the lower level and against the raise are two 

 stopes where on account of the value of the ore, none 

 has been left to form a floor. Here the timbering of 

 the drift has been made heavier and a floor of poles 

 laid over it to hold the broken ore. 



In one of the open stopes of the upper level the 

 walls incline to bulge inwards so that broken ore left 

 in the stope would bind and could not be drawn ofl". 

 In this stope ore has been removed as fast as broken. 

 The walls are kept apart by round cross timbers called 



[10] 



