24: National Geographic Magazine. 



values be perceived that are essential to good study. The illus- 

 trations should he of actual scenes; or, if designs, they should be 

 designed by a geographic artist. The descriptions should wher- 

 ever possible be taken from original sources, in which the narra- 

 tor tells what he saw himself. It is, to be sure, not always possi- 

 ble to know what kind of a form he describes, owing to lack of 

 technical terms, but many useful examples can be found that may 

 then be referred to their proper place in the system of geographic 

 classification that is adopted. 



I shall consider only one example in detail to show how far 

 short, as it seems to me, geography fails of its great opportunity, 

 both as taught in schools and as applied in after life. 



In northeastern Pennsylvania there are several water-falls that 

 leap over tilted beds of rock. Such falls are known to be of rare 

 occurrence, and we may therefore inquire into the cause of their 

 rarity and the significance of their occurrence in the region re- 

 ferred to. 



We may first look at the general conditions of the occurrence 

 of water-falls. They indicate points of sharply contrasted hard- 

 ness in the rocks of the stream channel, and they show that the 

 part of the channel above the fall has not yet been cut down to 

 base level. When the channel reaches base level there can be no> 

 falls. Now it is known from the general history of rivers that 

 only a short part of their long lives is spent in cutting their chan- 

 nels down to base level, except in the case of headwater streams,, 

 which retain youthful characteristics even through the" maturity 

 of their main river. Consequently, it is not likely that at any 

 one time, as now, in the long lives of our many rivers, we should 

 see many of them in their short-lived youthful phase. Falls are 

 exceptional and denote immaturity. They endure a little longer 

 on horizontal beds, which must be cut back perhaps many miles up 

 stream before the fall disappears, than on tilted beds, which must 

 be cut down a few thousand feet at most to reduce them to base 

 level. Falls on tilted beds are therefore of briefer duration than 

 on horizontal beds, and are at any time proportionately rarer. On 

 the headwater branches of a river where youthful features such 

 as steep slope and sudden fall remain after the main river has a 

 well-matured channel, we sometimes find many water-falls, as in 

 the still young branches of the old Ohio. These are like young 

 twigs on an old tree. But even here the rocks are horizontal, and 

 not tilted as in the cases under consideration. 



