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SCIENCE 



[N. S. Vol. X5XIX. No. 1009 



those of the crust, and that the great density 

 of the earth (5.6) is due to " compression by 

 pressure," in spite of the remarkable ineom- 

 pressibility of even water, with the interior 

 heat acting contrariwise. The most commonly 

 accepted view of the great weight of the 

 nucleus of the earth is that it is composed of 

 heavy metallic substances; for instance, 

 astronomer Ball regards meteorites as the re- 

 mains of disrupted planets such as would be 

 liberated by the explosion of the earth. 



Concerning the relationship between the 

 anomalies of gravity and earth movements. 

 Dr. Gilbert says : 



Spencer emphasizes the fact that there are large 

 plus anomalies within the region once covered by the 

 Laurentian ic« and regards it as proof that the 

 rising of the region after the removal of the ice 

 load was not caused by the removal of the load. 



Again he says : 



The fact (of plus anomalies within this area) 

 may equally be used to discredit the hypothesis 

 underlying his mode of interpreting anomalies. 



These statements give neither the facts nor 

 arguments upon which Spencer bases his 

 hypothesis that the anomalies are not due to 

 the removal of an ice load, nor how the facts 

 discredit his hypothesis. Observing that the 

 plus anomaly (equaling 700 feet of rock) 

 north of the Adirondacks, and the deforma- 

 tion (of 650 feet) of the earth's crust as seen 

 in the tilted beaches, closely agree, Spencer 

 naturally concluded that there is a direct rela- 

 tionship between the two phenomena. Farther 

 south in the Adirondacks, composed of dense 

 rocks, the anomaly of gravity is reduced to 

 200 feet of rock. Southward from this and 

 extending over a very great region once 

 covered by ice the anomalies show deficiency 

 of weight. If the deformation adjacent to the 

 St. Lawrence River were due to the removal 

 of the ice sheet, then the region to the south 

 should also have been elevated to isostate 

 equilibrium. 



Supporting Spencer's conclusions, from evi- 

 dence lying outside of the glaciated region, 

 the Appalachian belt and Florida are over- 

 weighted, although much material has been 

 removed from the mountains. On the other 

 hand, the coastal region is found to be under- 



loaded, although it is here that the deposition 

 of the materials, brought down from the 

 mountains, have accumulated. This under- 

 loading agrees with the subsidence shown by 

 the canyons and valleys indenting the sub- 

 marine border of the continent. Yet this 

 collateral evidence is not considered by Gilbert. 



The observation of all these features is of 

 comparatively recent date, yet they have the 

 greatest value, although they are contrary to 

 the hypothesis that the mobility of the earth's 

 crust is so complete that areas of considerable 

 size can not either be loaded or unloaded, 

 without being fully accounted for in the iso- 

 static balance. The phenomena of earth move- 

 ments and of anomalies of gravity introduces 

 new features in the evolution of our conti- 

 nents, which have only begun to be inves- 

 tigated. 



It may be added that Professor Leverett and 

 also Mr. Taylor have just announced that they 

 have found moraines in the lake region, in 

 disagreement with the hypothesis that the 

 deformation of the earth's crust is due to the 

 removal of the ice — results in accord with 

 relationship of the anomalies of gravity and 

 earth movements as lately first described by 

 the present writer. 



J. W. Spencer 



HEADS OF departments: a commentary upon 

 DR. Johnston's article 



It was very wholesome reading that Doctor 

 Johnston ofl^ered the heads of departments in 

 his article upon University Organization, ap- 

 pearing in the December 26 issue of Science, 

 p. 908. The unfortunate conditions described 

 so truly he evidently finds existing not in any 

 one special institution, but in many. 



Any fair-minded head realizes the disad- 

 vantages under which younger members of 

 his staff labor. Unfortunately, there are many 

 professors who are quite content to allow 

 their associates to remain unheard and un- 

 heeded, either because they honestly (and 

 ignorantly) believe them lacking in wisdom 

 or because they fear the effect of allowing 

 them to be in the least prominent. For such, 

 as well as for the more liberally inclined. 



