PHYSIOGRAPHIC PROBLEMS OF TODAY 541 



earth's atmosphere as well as the changes it is now undergoing, is a 

 theme in which the physiographer is profoundly interested. 



Volcanic mountains are numbered among the most awe-inspiring ■ 

 of topographic forms; the solid additions which volcanoes make to 

 the surface of the lithosphere are in view, and the contributions to 

 the atmosphere of vapors and gases from the same sources are tangi- 

 ble facts; but another phase of the great problem is also of interest 

 to the physiographer, namely, what changes take place in the rigid 

 outer shell of the earth by reason of the transfer of such vast volumes 

 of material as are known to have occurred from deep within the earth 

 to its surface. The magmas which have been caused to migrate and 

 come to rest for a time, either as intrusions within the earth's outer 

 shell, or as extrusions on its surface, are measurable in millions of 

 cubic miles. In connection with the profound questions concerning 

 the formation of folds and fractures in the earth's crust, an agency 

 is thus suggested comparable in importance with loss of heat, as 

 under the nebular hypothesis, or with gravitational compression, as 

 explained by the planetesimal hypothesis. In the many discussions 

 that have appeared as to the adequacy of earth contraction to account 

 for the origin of mountains of the Appalachian type, I have been able 

 to find but one mention of the role played by the transfer of matter 

 from deep within the earth outward, and in part its extrusion at the 

 surface, in causing folds in the crust from beneath which it was 

 derived. Problems of fundamental importance are outlined by the 

 considerations under review. 



To the immediate question, What is the best plan for enlarging 

 our knowledge of the physiography of volcanoes? the. reply seems 

 pertinent: Press on with the study of both active and dormant or 

 extinct examples. In this connection it should be remembered that, 

 while the individual volcanoes and volcanic mountains which have 

 been critically studied can be enumerated on the fingers of one's 

 hands, those which are practically unknown number many thousands. 

 The fact that Mont Pele and La Soufriere of St. Vincent during their 

 recent periods of activity furnished examples of at least two important 

 phases of volcanic eruptions not previously recognized is an assur- 

 ance of rich returns when other eruptions are critically investigated. 

 - While it is difficult to formulate the precise questions so numerous 



