To determine when, how far, and by what methods to develop this water power from lakes and rivers for the use of the people and to make this substitution, is another of our great economic problems.
Petroleum and natural gas, of which our original reservoirs were perhaps the richest in the world, are being rapidly exhausted.

These may be merely mentioned as being related to coal in the source of their supply, in the nature of their uses, and in the economic problems to which they give rise.
Sec.10.

#Transportation agencies#.

First to mention among the means of transportation are the navigable waters--oceans, lakes, rivers, and canals, with the necessary equipment of dredged inlets, harbors, docks, locks, and lighthouses.

Few of these appear in the total of "capitals," for they are not in private possession.