UTILITIES FOR HANDLING RAW MATERIAL. 67 



inland seas wherein the iron ore is conveyed from the Lake Superior 

 mining district to the ports adjacent to the blast furnaces of the 

 Middle West are employed the various forms of hoisting and conveying 

 apparatus, all of American origin, which probably constitute the most 

 famous of all the installations for transportation purposes. In this 

 field of activity methods advanced, at a single step, from the old plan 

 of unloading the vessels by means of wheelbarrows and permanent 

 trestles to the bridge tramway structures which are up to the present 

 date in almost universal use. 



The conspicuous elements in any such installation embrace the 

 elevated tramway spanning the dumping ground or railroad yard and 



Steam Shovel. 



connecting it with the vessels the trolley or carriage traversing this 

 tramway and the system of mechanism by which the whole is operated 

 and controlled. Such an apparatus is operated, of course, by a motive 

 power located beyond the limit of travel, and while the operation is at 

 every stage subject to the control of an operator, a large proportion of 

 the important functions are automatic, the positive movements of the 

 parts through such operations being derived entirely from the bodily 

 movement of the apparatus itself, while actuated by momentum, 

 gravity or the direct action of the hoist rope. Attached to the trolley 

 of each machine is an automatic dumping-tub or bucket, the dis- 

 charge of which may be made at the will of the operator, either at the 



