624 PHYSIOGRAPHY 



astronomy, meteorology, and physiogeography in the study of the 

 exogene processes. 



Whatever the solution of this problem may be, there will yet 

 remain a further question. When we compare the total amount of 

 erosion going on over the land with the total amount of rock which 

 was formed at the expense of preexistent continents, we find that 

 the latter is far greater than the former. According to the present 

 intensity of erosion and denudation, it would require an incom- 

 prehensibly large number of millions of years in order to produce 

 a volume of rock equal to that now comprised in the sedimentary 

 series. Estimates of the time elapsed since the earth, under present 

 physiogeographic conditions, has been the theater of the processes 

 to-day active upon the earth's surface, lead us by other routes to the 

 same conclusion. The influences of the sun's rays upon the exterior 

 of our planet have been felt for an incomparably long time, and we 

 cannot assert that there is any sensible decrease of their intensity. 

 Yet the sun's energy cannot be inexhaustible. Here we find a lack 

 of harmony, according to the present state of our knowledge, between 

 cause and effect, which is much in need of explanation. Questions 

 brought up by the physiogeographic method of studying the earth 

 are appealing, not only to astronomy, but to astrophysics. 



Thus our point of view passes from the earth's surface to the 

 earth as a whole, and from the earth as a whole to the sun, just as 

 soon as we begin to compare the phenomena which are taking place 

 upon our planet with the work performed by him. The broader the 

 circle to which we turn with questions, the greater the number of 

 problems which present themselves. We are thus more and more 

 strongly compelled to acknowledge that the key to success lies in an 

 organized cooperation among the different sciences, and any hard- 

 and-fast barring-off of the one from the other, or even the con- 

 temptuous disdain of one by another, will have evil results. It is 

 true that they have different refinements of method, but all pro- 

 blems do not permit of a mathematical treatment, and it is also true 

 that at times the one may make such a marked advance that it 

 grows over the heads of the others and is able from its more advanced 

 standpoint to point out the direction along which the others must 

 develop. But in the long run they must all advance evenly together 

 as long as they stand on the firm foundation of their individual fields 

 of observation. Physiogeography has such a field of observation in 

 the land surface, since it considers that as the surface upon which 

 light and heat fall from without, and through which the warmth 

 of the earth's body must pass from within outwards. 



The position occupied by geography among the other sciences 

 has been the subject of many discussions during the past decade; 

 and there is, especially in German, a rather large literature on the 



