206 FIRST YEAR COURSE IN GENERAL SCIENCE 



formations are called veins. They may contain grains of 

 copper, gold, and silver, with quartz and other minerals. 

 Sometimes the material filling the vein is a compound of 

 a metal, and by reduction the pure metal can be obtained. 

 230. Mining. Metal-bearing veins occur oftenest in 

 regions of disturbed and broken rocks which are found in 

 the mountain folds. If the upper rock is fractured or is 

 soft, it becomes worn away and thus a vein may be ex- 



FIG. 106. INTERIOR OF A MINE 



This tunnel enters the mountain horizontally. The large pipes furnish 

 compressed air for running machinery for drilling. The track is for trans- 

 portation of materials used in or procured from the mine. 1. Mention 

 material of both kinds. 2. Is it better to have a level or an inclined track? 

 Why? 



posed for a short distance. In other instances, particles of 

 the metal, or its ore, may be found on the mountain slope, 

 but the end of the vein itself may be as completely covered 

 with fallen rock waste as the rest of the mountain side. 

 Mines are frequently opened on the slopes of a mountain, 

 where by tunneling horizontally many veins may be crossed. 

 The most promising vein is then followed as far as possible. 



