148 ELEMENTS OF GENERAL SCIENCE 



there is on a railway ; on the other hand, it does cost a great 

 deal to provide and maintain harbors and docks. On the whole, 

 however, the expense per ton for moving freight by water is 

 usually less than by land. 



Water transportation is usually slower than transportation 

 by rail. In the shipment of such commodities as coal or lumber, 

 the demand for which it is possible to estimate many months 

 in advance, it is necessary to start the freight on its way a 

 little earlier, so as to allow plenty of time. It is not always 

 true, however, that the railways are more rapid. Sometimes 

 the railways are so crowded that the freight is not sent on 

 promptly or cars are allowed to stand on sidetracks for days. 

 A ship, on the other hand, usually proceeds quite promptly- 

 from one port to another. It may move more slowly, but since 

 it does not stop so long or so often, it may arrive before the 

 car does. Heavy and bulky articles, such as coal, iron ore, 

 stone, lumber, and grain, are commonly transported by the 

 lake route where this is possible. One of the most important 

 phases of the use of the lakes to-day is the transportation of 

 iron from the mines near the west end of Lake Superior and 

 near Green Bay to the iron and steel plants on the shores of 

 lakes Michigan and Erie. The great furnaces of South Chi- 

 cago, Indiana Harbor, and Gary at the south end of Lake 

 Michigan are supplied by lines of steamers which run directly 

 from the ore docks on Lake Superior and on Green Bay to 

 the private wharves of the steel plants. These boats are built 

 for this service and carry no other freight. Other lines of boats 

 run through lakes Huron, St. Clair, and Erie to Cleveland and 

 other ports on Lake Erie, where the iron ore is either smelted 

 or shipped to inland points, such as Pittsburgh. Other impor- 

 tant articles of commerce on the Great Lakes are coal, grain, 

 and lumber. 



There can be no doubt that the commerce which is carried 

 on upon the lakes is of great importance to the lake ports. 

 Many of their industries depend largely upon the materials 



