28o EDITORIAL 



The Evolution 0} Earth Structure. New York: Longmans, Green 

 & Co., 1903. By T. Mellard Reade. 



The author concludes that the continents and ocean basins arise from 

 differences in the specific gravities of large sections of the earth. These 

 specific gravities are not stable, but are subject to slow changes consequent 

 upon changes of temperature. A rise of temperature and local increase of 

 volume create protuberances which may be of continental extent. A fall 

 of temperature and decrease of volume lead to depressions,- which may cul- 

 minate in the formation of deeps. "Thus it follows that these departures 

 from the regular spheroidal forms are not original and permanent; nor are 

 they features which have been growing from the dawn of geological history, 

 such as would be likely to occur from a differential radial shrinkage of the 

 earth." Evidence of thermal fluctuations is given by the varying composi- 

 tion, specific gravity, and temperature of lavas from time to time emitted 

 from vents. "The extrusion of lavas is largely due to increase of tempera- 

 ture and consequent increase of volume. Relief by extrusion causes a 

 reduction of temperature, and shrinkage takes place in the supplying reser- 

 voir. This results in a subsequent period of quiescence, which lasts until 

 the molten matter of the reservoir again becomes hot enough to compel 

 extrusion." 



The author holds tenaciously to the theory which he advanced in a former 

 work,^ that mountain ranges are caused by sedimentation and a subsequent 

 heating of the sediments. Numerous cuts of models illustrating earth 

 movements are introduced, with a full discussion of the experiments. 



W. H. E. 



NOTE OF EXPLANATION. 



By an oversight, Maps I and II (Ten Mile Creek) of the paper of 

 Mr. George C. Matson entitled "A Contribution to the Study of the 

 Interglacial Gorge Problem," which appeared in the February-March 

 number of the Journal, were omitted. They are inclosed with this 

 number, and may be inserted between pages 140 and 141 of the 

 February- March number. 



I The Origin of Mountain Ranges. 



