622 . PHYSIOGRAPHY 



geographic correlation in their vicinity, and for a long time we were 

 inclined to ascribe all changes of climate to telluric processes. The 

 studies of the glacial period no longer allow us to retain these theories. 

 But there remains the attractive physiogeographic problem to 

 determine the number of possible changes of climate which may 

 result from geomorphologic causes. 



If, on the one hand, changes in the distribution and mass of 

 the great forms of the earth's surface produce far-reaching results in 

 the natural features of the surrounding lands, and if the finer mod- 

 eling of broad areas of land may be wholly changed because they 

 have been transferred from a region of dry, continental climate 

 into that of the oceanic climate without having changed their posi- 

 tion with reference to the earth as a whole, on the other hand, the 

 forces at work on the earth's surface also exert an undeniable influ- 

 ence upon the greater features in the surficial forms of our planet. 

 The destroying power of flowing water works most vigorously 

 where the greatest inequalities exist, not only because the water here 

 has the greatest distance to fall through, but because the great in- 

 crease in precipitation resulting from those inequalities produces 

 a greater mass of running water. Climatic controls result in cli- 

 matic divisions or boundaries. Bays become silted up by the rivers, 

 promontories are worn away by the attack of the ocean; thus the 

 horizontal arrangement of the land areas is disturbed, which is 

 an extraordinarily important factor from the physiogeographic stand- 

 point. Under the influence of the exogene forces all the abrupt con- 

 trasts of form disappear, and at the same time the causes for the 

 yet sharper contrasts in the organic phenomena of the lands are 

 removed. In this respect also it will become possible to establish 

 a sequence in development similar to the sequence in morphologic 

 development, and to place alongside of the geographic cycle of Davis 

 a physiogeographic cycle. The final stage of this physiogeographic 

 cycle would present a complete adjustment between the forms of 

 the earth's surface and all those exogene processes which are active 

 upon it. 



If, now, we review the earth's surface, whether from the mor- 

 phologic or from the physiographic standpoint, it is clear that 

 taken as a whole it is very far removed from the stage of old age. 

 Everywhere we notice traces of young crustal movements which 

 are repeatedly and abruptly disturbing that adjustment which the 

 exogene forces are constantly endeavoring to establish. Although 

 we may readily observe the theater of action of the exogene forces, 

 and easily recognize their distribution over broad areas, we are still 

 in the depths of darkness as regards knowledge of the distribution 

 of the disturbing endogene forces. It has been repeatedly attempted 

 to find some sort of relation between these forces and the earth as 



