RELATIONS TO OTHER SCIENCES 623 



a whole. The French investigators more especially have referred 

 sometimes to a dodecahedron and sometimes to a tetrahedron 

 which should express the ground-plan of the earth's crust. The 

 location of mountain ranges along both flanks of the continents of 

 North and South America has given rise to an attempt to establish 

 a relation between the distribution of mountain ranges and the 

 outlines of the continents. Great weight has also been laid upon the 

 occurrence of volcanoes along the edges of the continental blocks. 

 Edward Suess, who has undertaken the correlation of the different 

 portions of the crust, has emphasized the relations existing between 

 folded mountain ranges and the massive rocks which stand in front 

 of them. Although studies along the latter line have yielded some 

 very pretty isolated results, yet it is not safe to assume that these 

 various attempts have revealed to us the ground-plan of crustal 

 movements with respect to the degree of elevation or depression 

 and the strike of the zone of compression. Indeed, it seems as though 

 the analytic method heretofore pursued will not accomplish anything 

 until we are able to deduce a mental picture of the sequence of pro- 

 cesses in the development of the zones of compression. The contrast 

 between the structure of such zones and the structure of the border- 

 ing regions invites the application of such a method. 



In this respect we may hope for considerable enlightenment as 

 the result of further investigations in geophysics. It is easy to see 

 that the modeling of the earth's surface influences the radiation of 

 heat by the earth quite as strongly as it does the warming of the 

 earth by absorption of external heat. The water collected in the great 

 basins of the ocean reacts upon the warm earth body as a cooling 

 apparatus on a large scale, while the elevation of the land per- 

 forms the functions of a protecting cover, now thicker, now thinner, 

 which tends to prevent the loss of heat. Systematic investigations, 

 on islands as w r ell as mainland, into the geothermal gradients would 

 give us a basis for quantitative knowledge regarding the influence 

 of the surface features upon the radiation of heat by the earth. Just 

 as the surface isotherms, which Humboldt first drew for us, gave us 

 the first clear conception of the climate of the earth, so must we look 

 to geographic presentation of the isogeotherms for a reliable under- 

 standing of the intracrustal distribution of heat. These would serve 

 as a basis for further investigations, provided geophysical inves- 

 tigations continue to clarify our understanding of the conditions 

 prevailing in the abysmal masses. The problem of the crustal 

 movements of the earth can only be solved, if we may obtain in 

 addition to its complicated composition the relation existing be- 

 tween the earth's crust and the overlying and underlying masses. 

 This can only take place if physiogeography, geology, and geo- 

 physics cooperate as heartily in this line of investigation as have 



