134 National Geographic Magazine. 



would confine the origin of all seismical and volcanic disturban- 

 ces and their consequent Geogra;phical changes, to a mere shell of 

 the crust.* The result of the computation is certainly interest- 

 ing and we may hope will not be lost sight of in future discus- 

 sions, however it may share in gaining support or opposition. It 

 is based upon an assumption of the temperature when the earth 

 began to cool, to assume a lower temperature draws the belt 

 nearer to the surface and a higher temperature is believed to be 

 inconsistent with our knowledge of what heat may effect. This 

 belt is stated to be gradually sinking, however, and the computa- 

 tion, therefore, involves a term representing time, and I venture to 

 suggest as estimates of Geologic time are generally indefinite and 

 seem to be inexhaustible, an abundance can probably be supplied 

 to sink the belt deep enough for all theoretical purposes. 



More interesting to Geographers are the conceptions of ancient 

 forms suggested by the views recently advanced by Prof. Shaler 

 in a late number of Science (June 15, 1888), on "The Crenitic 

 Hypothesis and Mountain Building." To let the imagination have 

 full play, we may conceive that where we now have extensive 

 mountain ranges, there were formerly great plains of sedimenta- 

 tion, and where we see the process of sedimentation active to-day 

 there may be great mountains in the future. And also in his 

 inquiry into the " Origin of the divisions between the layers of 

 stratified rocks " (Proced. Boston Soc. Nat. Hist., vol. xxiii), we 

 may be carried away with the immensity of the changes sug- 

 gested. The recurring destruction of submarine life to contrib- 

 ute in the building of the rocks of the Continents : the appar- 

 ently endless cycles of emergence of the land and subsidence of 

 the waters, to leave the Geographical conditions we see to day, 

 furnish additional evidence of the wonders of the past and force 

 upon us anew the realization of how little in the great evolution 

 is the epoch in which we live. 



American Geologists have advanced the knowledge of the 

 world; only recently the American methods of Glacial study have 

 enabled Salisbury to interpret the terminal moraines of Northern 

 Germany (Am. Jour. Science, May, 1888), and that the Science 

 is active among our countrymen is evidenced by the formation of 

 a Geological Society and the establishment of a magazine de- 



* In the American Geologist for February, 1888, Prof. Reade protests 

 against the construction of the theory of a " belt or level of no strain" 

 placing the foci of earthquakes and other disturbances in the strata 

 above the belt. 



